Sensors for Handling Processing Technology Sensors for Force Pressure

R. Schulé • P. Waiblinger

Sensors for handlingand processing technology

Sensors for force and pressure

Learning System for Automation and Communications

Order No.: 090166Description: SENSOREN ARBB.Designation: D.LW-FP1130-GBStatus: 04/93Graphics: B. MatzkeLayout: 20.04.93, S.Durz, M. Schwarz, S. SperrfechterEditor: S. SperrfechterAuthors: R. Schulé, P. WaiblingerTranslator: A. Burns

© Copyright by Festo Didactic KG, D-7300 Esslingen 1, 1993

All rights reserved, including translation rights. No part of this publication maybe reproduced or transmitted in any form or by any means, electronic, mecha-nical, photocopying, or otherwise, without the prior written permission of FestoDidactic KG.

IntroductionLayout of the workbook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7What are sensors? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8User notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Equipment set FP1130 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Components-exercises table . . . . . . . . . . . . . . . . . . . . . . . . . 23

Table of contents

Course

Exercises

Force measurementA 1: Electrical behaviour of mechanically loaded

strain gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3A 2: Strain gauges connected in series . . . . . . . . . . . . . . . . . . A-11A 3: Connection of a measuring bridge amplifier . . . . . . . . . . . . . A-19A 4: Calibration of a force sensor using a quarter bridge circuit . . . . . A-27A 5: Calibration of a force sensor using a half-bridge circuit . . . . . . . A-35A 6: Calibration of an industrial force sensor . . . . . . . . . . . . . . . A-43A 7: Force measurement on pneumatic cylinders using an industrial

force sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-51

Pressure measurementA 8: Commissioning of an analogue pressure sensor . . . . . . . . . . . A-61A 9: Characteristic curve of an analogue pressure sensor . . . . . . . . A-69A10: Setting of a mechanical pressure switch . . . . . . . . . . . . . . . A-81A11: Setting of an electronic pressure switch . . . . . . . . . . . . . . . A-91A12: Using an electronic pressure switch

as a differential pressure switch . . . . . . . . . . . . . . . . . . A-101A13: Leak testing of compressed air reservoirs . . . . . . . . . . . . . A-111A14: Commissioning of a back pressure switch . . . . . . . . . . . . . A-121

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Fundamentals

B1: Force and force-related quantities . . . . . . . . . . . . . . . B-31.1 Definition of force . . . . . . . . . . . . . . . . . . . . . . . B-41.2 Types of force . . . . . . . . . . . . . . . . . . . . . . . . B-51.3 Force and counterforce . . . . . . . . . . . . . . . . . . . . B-81.4 Elastic and plastic deformation . . . . . . . . . . . . . . . . B-91.5 Force measuring methods . . . . . . . . . . . . . . . . . . B-101.6 Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-111.7 Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . B-121.8 Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-151.9 Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . B-16

B2: Elastic deformation . . . . . . . . . . . . . . . . . . . . . . . . B-172.1 Mechanical stress . . . . . . . . . . . . . . . . . . . . . . B-182.2 Hooke’s law . . . . . . . . . . . . . . . . . . . . . . . . . . B-202.3 Deflecting arm . . . . . . . . . . . . . . . . . . . . . . . . B-212.4 Torsion rod . . . . . . . . . . . . . . . . . . . . . . . . . . B-222.5 Technical design of spring elements . . . . . . . . . . . . B-24

B3: Strain gauges and additional force sensors . . . . . . . . . . B-273.1 Measurement of strain . . . . . . . . . . . . . . . . . . . . B-283.2 Piezoresistive effect . . . . . . . . . . . . . . . . . . . . . B-293.3 Semiconductor strain gauges . . . . . . . . . . . . . . . . B-323.4 Technical design . . . . . . . . . . . . . . . . . . . . . . . B-343.5 Application of strain gauges . . . . . . . . . . . . . . . . . B-353.6 Additional force sensors . . . . . . . . . . . . . . . . . . . B-36

B4: Acquisition of measuring data . . . . . . . . . . . . . . . . . B-374.1 Measuring chain . . . . . . . . . . . . . . . . . . . . . . . B-384.2 Wheatstone measuring bridge . . . . . . . . . . . . . . . . B-394.3 Compensating the effects of interference . . . . . . . . . . B-414.4 Elimination of line interferences . . . . . . . . . . . . . . . B-434.5 Industrial force sensors . . . . . . . . . . . . . . . . . . . . B-464.6 Measuring amplifiers . . . . . . . . . . . . . . . . . . . . . B-474.7 Output circuits . . . . . . . . . . . . . . . . . . . . . . . . B-494.8 Signal processing in digital systems . . . . . . . . . . . . . B-504.9 Signal transmission . . . . . . . . . . . . . . . . . . . . . . B-514.10 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . B-54

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B5: Technical design of force andtorque sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-555.1 Direct force measurement . . . . . . . . . . . . . . . . . . . . B-565.2 Indirect force measurement . . . . . . . . . . . . . . . . . . . B-575.3 Weight sensors . . . . . . . . . . . . . . . . . . . . . . . . . . B-585.4 Measurement of force components . . . . . . . . . . . . . . . B-595.5 Torque measurement . . . . . . . . . . . . . . . . . . . . . . . B-615.6 Dynamometer . . . . . . . . . . . . . . . . . . . . . . . . . . . B-625.7 Measuring plugs and strain sensors . . . . . . . . . . . . . . . B-63

B6: Applications of force sensors . . . . . . . . . . . . . . . . . . . . B-656.1 Areas of application for force sensors . . . . . . . . . . . . . . B-666.2 Research and development . . . . . . . . . . . . . . . . . . . B-676.3 Production technology . . . . . . . . . . . . . . . . . . . . . . B-686.4 Assembly technology . . . . . . . . . . . . . . . . . . . . . . . B-696.5 Material flow systems . . . . . . . . . . . . . . . . . . . . . . . B-716.6 Materials management . . . . . . . . . . . . . . . . . . . . . . B-726.7 Quality assurance . . . . . . . . . . . . . . . . . . . . . . . . B-73

B7: Technical design of pressure sensors . . . . . . . . . . . . . . . B-757.1 Pressure sensors . . . . . . . . . . . . . . . . . . . . . . . . . B-767.2 Diaphragm pressure sensors . . . . . . . . . . . . . . . . . . . B-787.3 Pressure sensors with strain gauges . . . . . . . . . . . . . . . B-807.4 Monolithic pressure sensors . . . . . . . . . . . . . . . . . . . B-817.5 Piezoelectric pressure sensors . . . . . . . . . . . . . . . . . . B-837.6 Special designs . . . . . . . . . . . . . . . . . . . . . . . . . . B-837.7 Indirect pressure sensors . . . . . . . . . . . . . . . . . . . . . B-847.8 Operating conditions . . . . . . . . . . . . . . . . . . . . . . . B-85

B8: Applications for pressure sensors . . . . . . . . . . . . . . . . . B-878.1 Areas of application for pressure sensors . . . . . . . . . . . . B-888.2 Research and development . . . . . . . . . . . . . . . . . . . B-898.3 Production technology . . . . . . . . . . . . . . . . . . . . . . B-908.4 Assembly technology . . . . . . . . . . . . . . . . . . . . . . . B-918.5 Process technology . . . . . . . . . . . . . . . . . . . . . . . . B-928.6 Materials management . . . . . . . . . . . . . . . . . . . . . . B-938.7 Quality assurance . . . . . . . . . . . . . . . . . . . . . . . . B-94

Bibliography of illustrations . . . . . . . . . . . . . . . . . . . . . . . . B-95

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Solutions

Exercises


strain gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . C-3A 2: Strain gauges connected in series . . . . . . . . . . . . . . . . C-5A 3: Connecting a measuring bridge amplifier . . . . . . . . . . . . . C-7A 4: Calibrating a force sensor using a quarter-bridge circuit . . . . . C-9A 5: Calibrating a force sensor using a half-bridge circuit . . . . . . . C-11A 6: Calibrating an industrial force sensor . . . . . . . . . . . . . . . C-13A 7: Force measurement on pneumatic cylinders using an industrial

force sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-15

Pressure measurementA 8: Commissioning of an analogue pressure sensor . . . . . . . . . C-17A 9: Characteristic curve of an analogue pressure sensor . . . . . . . C-19A10: Setting of a mechanical pressure switch . . . . . . . . . . . . . C-23A11: Setting of an electronic pressure switch . . . . . . . . . . . . . . C-25A12: Using an electronic pressure switch

as a differential pressure switch . . . . . . . . . . . . . . . . . . C-27A13: Leak testing of compressed air reservoirs . . . . . . . . . . . . C-29A14: Commissioning of a back pressure switch . . . . . . . . . . . . C-31

Appendix

Data sheets

3/2-way panel mounted valve . . . . . . . . . . . . . . . . . . . . 011422One-way flow control valve . . . . . . . . . . . . . . . . . . . . . . 011700Service unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 011758Connection unit 101AF . . . . . . . . . . . . . . . . . . . . . . . . 014595Pneumatic-electronic switch . . . . . . . . . . . . . . . . . . . . . 032188Distribution unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . 034080Signal switching unit . . . . . . . . . . . . . . . . . . . . . . . . . 150538Force sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150541Deflecting arm force sensor . . . . . . . . . . . . . . . . . . . . . 150542Pressure switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150554Pressure manifold . . . . . . . . . . . . . . . . . . . . . . . . . . 150555Analogue pressure sensor (10V/20mA) . . . . . . . . . . . . . . . 150556Compressed air reservoir . . . . . . . . . . . . . . . . . . . . . . . 150557Analogue pressure sensor (5V/20mA) . . . . . . . . . . . . . . . . 150558Measuring bridge amplifier . . . . . . . . . . . . . . . . . . . . . . 150563Back pressure switch . . . . . . . . . . . . . . . . . . . . . . . . . 150565Cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150578

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Introduction Festo Didactic

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Layout of the workbook

This workbook is part of the Learning System for Automation by Festo DidacticKG. The book has been designed for both course training as well as self-tuition.

The workbook D.LW-FP1130-GB (Order No. 090166) was designed forequipment set D.CP-FP1130 (Order No. 150531) of function package FP 1130.

The core subject of function package FP 1130 is sensors for force andpressure. The components are assembled on an aluminium profile plate. Themeasurements can be carried out by means of a digitial multimeter. Practicaland theoretical knowledge is conveyed regarding analogue force and pressuresensors as well as pressure switches. The sensor characteristics can bedetermined by means of experiments, e.g. accuracy, resolution, linearity andhysteresis.

The book is divided into:

• Section A "Course"• Section B "Fundamentals"• Section C "Solutions"• Section D "Appendix"

Section A – CourseThe course provides the required subject knowledge with the help of selectedexercises. The contents of the topics have been coordinated in that theexercises supplement one another, yet can be carried out independently.References point out further and more detailed information contained in boththe fundamentals section as well as in the collection of component data sheets.

Section B – FundamentalsThis part contains the theoretical fundamentals on the subject. Topics arearranged according to subject area. The fundamentals section can be workedthrough by chapter or used for reference.

Section C – SolutionsThis section features the solutions to the exercises in the course section.

Section D – AppendixThe final section of the book contains a collection of component data sheetsrelating to the equipment set.

The book can be incorporated into an existing training program.

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What are sensors?

A sensor is a technical converter which converts a physical value such astemperature, distance or pressure, into a different value, which is easier toevaluate. This is usually an electrical signal such as voltage, current, resistan-ce or frequency of oscillation. Alternative descriptions for sensors are en-coders, detectors or transducers.

1. Sensors andsensory organs

The word ‘sensor’ is derived from the latin ‘sensus’, in English ‘feeling’ or ‘sen-sation’. The efficiency of many sensors is based on technical developments insemiconductor technology. They are used predominantly for the acquisition ofmeasured data.

Sensor

Sensors can be broadly compared to the receptors of sensory organs, whichalso bring about the conversion of physical values, e.g. light, heat or soundpressure into a neuro-physiological sensation.

The efficiency of sensors and receptors for comparable measuring tasks orsensory perception respectively, varies considerably. As such our sensory or-gans perceive most values only approximately, and are therefore not suitablefor the measurement of absolute values.

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RodsPhotoresistor

Fig. 1: Comparison of sensor and receptor.Rods are receptors in the retina of the eyeand convey the black and white perception.


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The role of sensory organs consists primarily of the coordination of signalsfrom several receptors, as well as the partial processing and evaluation of thesignal. The human eye, for example, consists of the lens system, the iris dia-phragm, the retina and approximately 120 million light-sensitive rods and ap-proximately 6 million colour-sensitive cones. In addition to this are various mu-scles for the focussing of light beams and movement of the iris diaphragm. Assuch, some preliminary partial image processing already takes place in thenerve cells of the retina, e.g. the analysis of contours or movements. The brainthen processes the images on a higher level, which includes the automaticfocussing and control of the diaphragm, the perception of depth by means ofsuperimposing the images from both eyes, compensating auto-movement ofthe eye and all other body movements. All this takes place prior to the actual,conscious function of seeing.

Sensory organs

Here too, technology has adopted the line of copying the ingenuity of nature.Line or matrix-type configurations of several sensors of the same type, similarto CCD chips are described as sensor systems. CCD is the abreviation forCharge Coupled Device and describes a CCD chip constructed from chargecoupled semiconductors. The operational principle of a CCD chip is based onthe premises that the electrical charge created by the photoelectric effect in thesemiconductor is transmitted to a coupled memory, which is interrogated at acertain clock frequency.Similary, sensors where both sensor and signal processing are on the samesemiconductor chip, are known as sensor systems. However, these sensorsystems are still a long way off from achieving the complexity and capability ofsensory organs.

Sensor systems

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VIDEO

CCD Camera Eye

Fig. 2: Comparison of sensor system and sensory organ


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In addition to the integration of amplifiers, attempts are being made to incorpo-rate computing power into the sensor. This trend towards decentralised dataprocessing results in improved data throughput. This type of sensor system,described as a “smart sensor” both in English and in German, could be moreeasily compared to a sensory organ.

Smart sensor

With more recent micromechanical developments, the mechanical elements ofa sensor are also integrated into the silicon chip. Primarly, it is membrane,spring or oscillatory parts which are etched from silicon. Research laboratorieshave already succeeded in producing rotary and sliding connections, therebypaving the way for the construction of miniaturised mechanical devices. Micro-mechanics combine the excellent mechanical properties of silicon, in particularits high elasticity, with the special electrical properties.

Micromechanics

A further interesting trend is the development of so-called biological sensors.These consist of a biologically active part, e.g. enzymes or bacteria, and amicroelectronic part, which registers and processes the biological reactions.The first of these biological sensors are available specifically for the purpose oforganic substances, e.g. determining blood sugar value. However, the futuredevelopment of biological sensors cannot be predicted at this stage.

Biological sensors

1120Introduction Festo Didactic

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Sensors are used in many areas of science and technology. In research, hig-hly sensitive and specialised sensors are employed for the purpose of conduc-ting experiments. In automation technology, both standard as well as speciallydeveloped sensors are in use. In the case of equipment for basic require-ments, ordinary sensors are mainly used, though these need to function relia-bly and require no maintenance.

2. Use of sensors

This workbook deals mainly with the use of sensors in automation with regardto achieving important criteria such as:

• Cost reduction

• Rationalisation

• Automation

• Flexibility

• Environmental protection

The use of sensors is however also due to the inherent developments in tech-nology such as:

• increased sensitivity, precision, response rate and reliability,

• adaptation to further developments in design and technology,

• new technologies.

Sensors are therefore used in automation because they:

• provide early and reliable signalling of error functions in automated sy-stems, e.g. broken tools or congestion,

• localise the source of error as part of an intelligent error diagnosis,

• detect wearing tools,

• provide the measured values, which are required for continuous optimisati-on of the production process by means of adaptive control and adjustment,

• are used in automated quality control,

• monitor materials management and assist in automating material flow,

• perform product identification, which is essential in flexible automation,

• signal danger in the workplace, e.g. excessive concentration of pollutants,

• provide a more humane work environment, e.g. in the case of tiring ormonotonous visual inspection, monitoring and measuring tasks in a hazard-ous environment.


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Sensors are an integral part of complex equipment. In particular, the furtherdevelopment of robots will be based on the use of sensors. After all, even theCIM concept with all its technical, organisational and social structures wouldnot be feasible without the use of sensor modules.

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Fig. 3: A sensor monitors the assembly of a printed circuit board


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The wide range of sensors is first of all classified on the basis of the physicalquantity to be detected and secondly according to the operational principle ortype of application.

3. Classification ofsensors

• Sensors for dimensional quantities:position, distance, length, travel, strain, gradient, speed, acceleration, angleof rotation, rotation as well as surface characteristics of workpieces.

• Sensors for force-related quantities:force, weight, pressure, torque and mechanical efficiency.

• Sensors for values of material quantity:flow rates and filling level of gaseous, liquid or solid materials.

• Sensors for temperature and heat quantity.

• Sensors for evaluating quantities of optical radiance:radiant flux, radiant energy, radiant intensity, radiance and luminous quanti-ties such as luminous flux, luminous energy, luminous intensity, luminance,illuminance. Moreover, this category should include all systems for imageprocessing insofar as these are for the purpose of measuring tasks.

• Sensors for characteristics of acoustic waves:sound pressure, sound energy, sound level and audio frequency.

• Sensors for electromagnetic quantities:generally recognised elementary electrical quantities are voltage, current,electrical energy and power. Also included amongst these are electrical andmagnetic field force and electromagnetic emission. The latter is limited bythe above mentioned optical emission due to the wavelength suppositionλ > 10-3 m.

• Sensors for high-energy radiation:X-ray radiation, gamma radiation. The high-energy radiation is limited by theoptical emission due to the wavelength supposition λ < 10-10 m. Sensors forparticle radiation such as electrons, alpha particles, elementary particles andnuclear fragments.

• Sensors for chemical substances (gases, ions), and in particular water inthe form of humidity, dew-point and icing sensors.

• Sensors for physical material properties:mechanical, electrical, optical, thermal and acoustic properties.

• Sensors for identification of objects and pattern recognition:This category generally includes sensor systems such as optical characterreaders, bar code readers, magnetic strip readers and image processingsystems, which also could have been included in one of the previous cate-gories, but form a separate group due to their specialised field of applicati-on.


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Sensors convert a physical value, usually into an electrical signal. Sensors canbe divided, according to the type of output signal, into binary sensors, alsocalled switches, and analogue sensors.

4. Sensor signals

Binary sensors generate just two different output signals, i.e. the switchingstates “On” and “Off”. The changeover from one switching state to anothertakes place at a very specific value of the physical variable; this switchingvalue can often be set. In many instances, the switching point on the charac-teristic curve for an approaching object differs to that of a withdrawing object.The difference between the two switching points or threshold values is knownas hysteresis. In many applications, hysteresis can be quite favourable in thatit reduces the switching frequency in the case of closed loop control and leadsto improved stability of the system.

Binary sensors

Analogue sensors create an electrical signal which changes continually accor-ding to the constant change in physical value. This correlation need not neces-sarily be linear, but in contrast with binary sensors always indicates the actualsize of the physical value. Analogue sensors offer more information than binarysensors; though the processing of signals is more costly.

Analogue sensors


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t t0

1

t

s

V,

Displacement / Distance

Analogue sensor signal Switching signal

Linear potentiometer Proximity switch

Fig. 4: Analogue and binary signals

This diagram illustrates the connection between a displacement and the binaryand analogue sensor signals derived from this. In automation, analogue sen-sors are used, if a gradual change of the value is of significance. Binary sen-sors are however often used as limit monitors or alarm switches.


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In research laboratories, quality assurance and process monitoring alike, sen-sors provide information on a technical production sequence or a physical orchemical reaction. These functions are known as a process. The information isindicated to the operator by means of a display instrument or fed into a datarecording device, e.g. a computer. In this context, both the operator as well asthe data recording device should be regarded as information processing sy-stems. The term ‘processors’ is used to describe these systems.

5. Information flowin automation

In process measurement, information flows from the process via the sensor orgenerally speaking from the sensors to the processor.

Process measurement

In process control the information flow is the reverse. The operator or aprocessor intervenes in the process with the help of actuators. The informationflows from the processor to the process via the actuators.

Process control

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ProcessorsSignalprocessing

Sensors

Auxiliaryenergy

Process

Fig. 5: Information flow in measuring technology

ProcessActuatorsOutputunit

Auxiliaryenergy

Processors

Fig. 6: Information flow in control technology


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In automation technology, both types of information flow occur. The closedcircuit of information ressembles closed loop control technology, i.e. processorto process and back again to the processor, but places the emphasis on themethods of transmitting and processing information. Control loops can be partof an automation system.

Automation technology

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Processors

Process

Processenergy

Signalprocessing

Actuators

Controlenergy

Outputunit

Sensors

Auxiliaryenergy

Fig. 7: Information flow in automation


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User notes

Apart from the general notes on safety, the following operating notes should beobserved:

Setting the equipment for the measurements:

• Switch off voltage supply

• Complete the electrical circuit and note the polarity of the voltages to beconnected

• Check the circuit by means of the circuit diagram

• Switch on the power supply at a regulated voltage of 24 V D.C. / 5 A.

Having completed the measurements:

• Switch off power supply

• Disconnect measuring lines

When using electrical equipment, the colour codings for the connecting linesand plugs must be observed. The following table of colour abbreviations and therelevant data sheets in appendix D will enable you to establish the correctelectrical connections.

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Comments regarding theexercises in the coursesection


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The graphic symbols shown in respect of pressure switches and analoguepressure sensors in the pneumatic circuit diagrams are based on theISO/DIS standard 1219-1:

The equipment set includes two kinds of equipment with different types ofmounting. The equipment using a knurled screw and T-head nut can bescrewed directly on to the profile plate. The equipment using locating pins canalso be mounted on to a plug-in board and requires the use of plug-in adaptersfrom the set of adapters D.MP-B-ME-AS (Order No. 035651), in order to mountit on to the profile plate. In course A, the plug-in adapters are listed in thecomponent list as and when they are required.

A number of procedures or simplifications are required or defined in theexercises, which will not be individually described in each exercise. You shouldtherefore observe the following notes. Please refer also to the relevant datasheets in the appendix.

The electronic amplifier components of the measuring bridge amplifier aresubject to temperature drift until they reach their operating temperature. Due tothis, the zero-point of a sensor cannot be accurately set on the amplifier duringthe warming-up period. The amplifier must therefore be switched onapproximately 5 minutes before the exercise is carried out. After this period,temperature drift will no longer occur. The connections Out- and 0V areelectrically isolated. When carrying out measurements, these two connectionsmust not be linked or mixed up.

The force sensor contains the calibrating device D.AS-SGA. With the help ofthis device, a force can be applied to the sensor by means of a weighted discfrom the set of weights D.AS-S-GWS-FP1130.The colours of the connecting cables and the plugs do not always correspond.The plugs for the voltage supply and the signal lines, however, are the samecolour for each pair.In order to avoid damage, forces in excess of 200 N must not be applied to theforce sensor. As far as the introduction of force with cylinder D.AS-DSN-PPV isconcerned, air pressure must not exceed 4 bar on the piston side.

Graphic symbols

Assembly

Measuring bridge amplifier

Force sensor


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The connection plate D.ER-AE-101AF is a unit with which the analogue signalsare switched to the programmable logic controller FPC 101AF. The FPC 101AFcontroller is used in the function package FP1131. In the function packageFP1130, the connection plate D.ER-AE-101AF is used as a distributor unit foranalogue signals in conjunction with the signal changeover switchD.AS-SUAE-101.On the lefthand side of the connection plate, there is a 9-pin socket for theconnection of signals to the counter input of FPC 101AF. Because the counterinput is not used for carrying out the exercises with the equipment set ofFP1130, it has not been illustrated in any of the electrical connection diagrams.Care should be taken that the load connections of the analogue section (GND)and the voltage supply (0 V) are not connected together internally. For themeasuring tasks using the multimeter, the two load connections must always beconnected to one another.

The voltage signals are switched to output 0 via the signal switching unit, andthe current signals are switched to output 1. The unit switches the signals ofboth input sockets to the appropriate output socket for each switching position.

In the exercises using the set of weights, the following simplification applies withregard to determining force:

The distributor and connection plates are shown without the 24 V voltagesupply.

In each case, only the signal changeover switch is shown, but not the distributorand connection units.

The deflecting arm force sensor and the back pressure switch must beassembled above the profile plate. The following illustration shows the positionof the two components on the profile supports. It should be noted that thedeflecting arm force sensor must be mounted directly above the vertical profilerail. The deformation movement of the deflecting arm in the mechanical stop isapproximately 0.5 mm upwards and 1.5 mm downwards.An additional connection cable, a piece of tubing and a transparent plasticbeaker form part of the back pressure sensor unit. The lugs of the connectioncable are plugged into the electrical contacts of the back pressure switch. Theallocation of cable lugs and plug contacts is unimportant. The tubing isconnected to the pressure input (lower connection) of the back pressure switch.The upper connection remains vacant. The beaker is secured underneath theback pressure switch which is mounted on the profile, whereby the tubing isinserted in the beaker.

Connection plate

Signal switching unit

Electrical connectiondiagrams

Electrical circuit diagrams

Deflecting arm force sensorand back pressure switch

Equipment set FP1130Description

D.CP-FP-1130Designation

150531Order No.

* Two or four plug-in adapters from the set of adapters D.MP-B-ME-AS arerequired to assemble the designated units on the profile plate.One set of adapters contains 27 adapters.

1130

Quant. Order No. Description Designation

1 150554 Pressure switch D.ER-PEV-1/4-B

1 150556 Analogue pressure sensor D.ER-SDE-10-10V/20mA


2 150555 Pressure manifold D.ER.FR-4-1/8-B

1 150557 Compressed air reservoir D.ER-VZS-0,4

1 150565 Back pressure switch,including beaker, D.AS-RK

D.ER-SDS

1 150542 Deflecting arm D.ER-BB-KS-FP1130

1 150541 Force sensor, includingweight support D.AS-SGA

D.ER-KS-FP1130

1 034080 Distribution plate * D.ER-VERT-SENSOR

1 014595 Connection plate * D.ER-AE-101AF

1 150538 Signal switching unit D.AS-SUAE-101

1 034009 Set of weights D.AS-GWS

1 150543 Set of round weights D.AS-S-GWS-FP1130

1 150563 Measuring bridge amplifier * D.ER-BV-FP1130

1 032188 Pneum.-elect. switch * D.ER-PEN-M5

1 011700 One-way flow control valve * D.ER-GR-1/8 B

1 011422 Panel mounted valve * D.ER-SV-3-M5

1 011758 Service unit * D.ER-FRC-1/8-S

1 115608 Profile 32x32x168 C/C

1 107635 Profile 32x32x170 B/B

1 035651 Set of adapters D.MP-B-ME-AS

1 150578 Cylinder * D.AS-DSN-PPV


22

Components-exercises table

1130

Components,Description, Designation

Exercises

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Pressure switchD.ER-PEV-1/4-B

1 1

Analogue pressure sensorD.ER-SDE-10-10V/20m

1 1 1 1 1 1 1

Analogue pressure sensorD.ER-SDE-10-5V/20mA

1

Pressure manifoldD.ER-FR-4-1/8-B

1 1 1 1 1 2 1

Compressed air reservoirD.ER-VZS-0,4

1 1

Back-pressure switchD.ER-SDS with beaker

1

Force sensorD.ER-KS-FP1130with weight support

1 1

Distribution plateD.ER-VERT-SENSOR

1 1 1 1 1

Connection plateD.ER-AE-101AF

1 1 1 1 1 1 1


23

1130

Component,Description, Designation

Exercises

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Signal switching unitD.AS-SUAE-101

1 1 1 1 1 1 1

Set of weightsD.AS-GWS

1 1

Set of round weightsD.AS-S-GWS-FP1130

1

Measuring bridge amplifierD.ER-BV-FP1130

1 1 1 1 1

Pneum.-elect. switchD.ER-PEN-M5

1 1

Deflecting arm force sensorD.ER-BB-KS-FP1130

1 1 1 1 1

One-way flow control valveD.ER-GR-1/8B

1 1

Panel mounted valveD.ER-SV-3-M5

1 1

Service unitD.ER-FRC-1/8-S

1 1 1 1 1 1 1

CylinderD.AS-DSN-PPV

1

Digital multimeterD.AS-DMM *

1 1 1 1 1 1 2 1 1 1 1 1 1 1

* not included in equipment set (separate accessory, Order No. 035 681)


24

Course

Exercises

Force measurement

A 1: Electrical behaviour of mechanically loadedstrain gauges . . . . . . . . . . . . . . . . . . . . . . A-3

A 2: Strain gauges connected in series . . . . . . . . . . . . . A-11A 3: Connection of a measuring bridge amplifier . . . . . . . . . . A-19A 4: Calibration of a force sensor using a quarter-bridge circuit . . . . A-27A 5: Calibration of a force sensor using a half-bridge circuit . . . . . A-35A 6: Calibration of an industrial force sensor . . . . . . . . . . . A-43A 7: Force measurement on pneumatic cylinders using an industrial

force sensor . . . . . . . . . . . . . . . . . . . . . . A-51

Pressure measurement

A 8: Commissioning of an analogue pressure sensor . . . . . . . . A-61A 9: Characteristic curve of an analogue pressure sensor . . . . . . A-69A10: Setting of a mechanical pressure switch . . . . . . . . . . . A-81A11: Setting of an electronic pressure switch . . . . . . . . . . . A-91A12: Using an electronic pressure switch

as a differential pressure switch . . . . . . . . . . . . . A-101A13: Leak testing of compressed air reservoirs . . . . . . . . . A-111A14: Commissioning of a back pressure switch . . . . . . . . . A-121

1130

A

Course Festo Didactic

A-1

1130

A

Course Festo Didactic

A-2

Sensors for force and pressure Subject

Electrical behaviour of mechanically loaded strain gauges Title

To learn about the electrical behaviour of strain gauges (SG) under tensionand compression.

Learning content

Strain gauges (SG) consist of a resistance layer. The resistance value increa-ses, if the strain gauge is tensioned in the direction of the resistance paths. Itdecreases if the strain gauge is compressed. The resistance change is basedon the change in length, cross section and specific resistance as a result of thetension or the compression.

Technical knowledge

A deflecting arm with two opposing strain gauges is used for force measure-ment. In order to examine the electrical behaviour of the strain gauges in prin-ciple, a load is to be applied lightly to the deflecting arm by hand while theresulting electrical behaviour of the strain gauges is observed.

Problem definition

1130

A 1

1

2

Fig. 1/1: Deflecting arm

1) Deflecting arm2) Strain gauge

B 3.2

Exercise sheet Festo Didactic

A-3

a) Connect the upper strain gauge to the multimeter for a resistance measure-ment.

Exercise

b) Lightly press down the deflecting arm and determine the qualitative resi-stance change of the strain gauge.

c) Lightly press the deflecting arm upwards and establish the qualitative resi-stance change of the strain gauge.

d) Calculate the percentage resistance change of the measurement in exerci-se part b).

Please observe the user notes in the introduction section when carrying outthe exercises. Appropriate information regarding connection method and addi-tional technical data can be found in the corresponding data sheets in theappendix.

1130

A 1


A-4

The connection cables of the upper strain gauge are connected directly to themultimeter.

Practical implementationPart exercise a)

1130

A 1

+

_

Cx

A COMA/mA

!

10A

u

!

400mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nF

Fu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

1

2

BK

WH

WH

BK

Fig. 1/2: Electrical connection

Comp.Ref. No.

Qty. Description Designation

1 1 Deflecting arm force sensor D.ER-BB-KS-FP1130

2 1 Digital multimeter D.AS-DMM

Table 1/1: Component list


A-5

The resistance of the strain gauge is approximately 350 Ohm. The nearestlarger measuring range is to be set on the multimeter.

Note

SG

1130

A 1

R

Fig. 1/3: Electrical circuit diagram


A-6

If you press down the deflecting arm slightly with your finger, the multimeterregisters a signal change. The force applied should not be excessive, becausedeformation of the deflecting arm should only occur within its range of elasticity.

Part exercise b)

• Record the qualitative signal change in table 1/2 on the worksheet.

1130

A 1

+

_

Cx

A COMA/ mA

!

10A

u

!

400 mAMAX

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 2 0 30 4 0

BK

F

BK

WH

WH

Fig. 1/4: Test procedure


A-7

• Press the deflecting arm upwards with roughly the same amount of force asthat used in part exercise b).

Part exercise c)

It may be necessary to remove the mechanical stop in order to carry out theexercise. If so, please note that there must not be any plastic deformation ofthe deflecting arm.

Note

• Record the qualitative signal change in table 1/3 of the worksheet.

The percentage resistance change ∆R%is calculated as follows:Part exercise d)

∆ R% = ∆ RSGRSG

⋅ 100

• Calculate the percentage resistance change for the measurement in partexercise b).

• Enter the value in table 1/4 of the worksheet.

Estimate the resistance behaviour of the strain gauge in the unloaded stateafter plastic deformation of the deflecting arm has occurred.

Question

1130

A 1

+

_

Cx

A COMA/ mA

!

10A

u

!

400 mAMAX

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 2 0 30 4 0

BK

F

BK

WHWH



A-8

Answer

1130

A 1

Worksheet Festo Didactic

Resistance of unloaded SG:____________________Ohm

Change of resistance ∆RSG = _____________Ohm

The resistance of the loaded SG is:

increasing

decreasing

the same

Table 1/2: Qualitative signal change of a strain gauge with tensile stress

Resistance of unloaded SG:____________________Ohm

Change of resistance ∆RSG = _____________Ohm


increasing

decreasing

the same

Table 1/3: Qualitative signal change of a strain gauge with compressive stress

Percentage resistance change ∆R% = ________________%

Table 1/4: Percentage resistance change

A-9

Notes

Worksheet Festo Didactic1130

A 1

A-10


Strain gauges connected in series Title

To learn about the electrical behaviour of strain gauges connected in series. Learning content

If a load is applied to a deflecting arm, a mechanical stress is created, whichleads to strain of the material. Depending on the amount of stress, this isgreatest on the upper and lower surface of the deflecting arm at the point ofclamping. If force is applied downwards strain is positive on the upper side andnegative on the lower side. Positive strain is known as tension. Negative strainis also known as compression. For simplicity, we can assume that both strainsare of equal magnitude.

Technical knowledge

The principle of the electrical behaviour of loaded strain gauges, which areinterconnected, is to be investigated.

Problem definition

1130

A 2

B 2.3

2

3

1

4

Fig. 2/1: Loaded deflecting arm

1) Deflecting arm2) Upper strain gauge strip

3) Lower strain gauge strip4) Load


A-11

a) Connect the two strain gauges in series to the multimeter for resistancemeasurement.

Exercise

b) Lightly press the deflecting arm downwards and determine the qualitativeresistance change of the two strain gauges.

c) Lightly press the deflecting arm upwards and determine the qualitative resi-stance change of the two strain gauges.


1130

A 2


A-12

The two strain gauges are connected in series to the multimeter. Because thestrain gauges in question are resistors, order and polarity are unimportant.


• Connect one black plug (BK) of the upper strain gauge to a white plug(WH) of the lower strain gauge. Plug in the two free connectors to themultimeter for resistance measurement.

1130

A 2

+

_

Cx

A COMA/mA

!

10A

u

!

400mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

m Am V

V

nFFu

AuTTL

DA TA HO LD

PEAK HOLD

DC......

A C

A UT O

R A N G E

_+

0 10 20 30 40

BKWH

BK

WH

2

1


Comp.Ref. No.






A-13

• Lightly press down the deflecting arm using your finger. Ensure that theforce applied is not excessive. The deflecting arm must be deformed onlywithin its elastic range.

Part exercise b)

• Record the qualitative signal change in table 2/2 of the worksheet.

SG

SG

1130

A 2

R


F+

_

Cx

A CO MA/ mA

!

10A

u

!

40 0m AM A X

500 V MAX

!

750V1000V.....

VTTL

OFF

A

m Am V

V

nFFu

AuTTL

DA TA HO LD

PEAK HOLD

DC......

AC

AUTO

R A N G E

_+

0 10 20 30 40

BKWH

BK

WH



A-14

• Press the deflecting arm upwards with roughly the same amount of force asthat used in part exercise b).

Part exercise c)

It may be necessary to remove the mechanical stop in order to carry out thispart exercise. If so, please note that there must not be any plastic deformationon the deflecting arm.

Note

• Record the qualitative signal change in table 2/3 on the worksheet.

Assess the resistance behaviour of the two strain gauges connected in seriesin the unloaded state, after plastic deformation of the deflecting arm.

Question

1130

A 2

F

+

_

Cx

A COMA/mA

!

10A

u

!

400mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

m AmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

A C

A UT O

R A N G E

_+

0 10 20 30 40

BKWH

BK

WH



A-15

1130

A 2

Festo Didactic

A-16

Answer

Resistance of unloaded SG:_________________Ohm


increasing

decreasing

the same

Table 2/2: Qualitative signal change when pressed down

Resistance of unloaded SG:_________________Ohm


increasing

decreasing

the same

Table 2/3: Qualitative signal change when pressed upwards


A 2

A-17

Notes


A 2

A-18


Connection of a measuring bridge amplifier Title

Tests for signal evaluation of strain gauges using a bridge circuit and a measu-ring amplifier.

Learning content

A relative strain ε produces a relative change in the strain gauge resistance of

∆R/R = k ⋅ ε with k approx. 2. This resistance change causes a change in the

output signal of the quarter-bridge VA/VE = 1/4 ⋅ ∆R/R = 0.5 ε. Because abridge is not normally balanced, the zero compensator of the measuring ampli-fier adjusts the inherent error signal of the measuring bridge, therefore enab-ling the meter to display 0 V in the unloaded state. The amplification of thebridge signal thus permits trouble-free measurement and display of the signal.

Technical knowledge

In order to obtain meaningful measured values, the force sensor of the deflec-ting arm is to be connected to the measuring bridge amplifier and the amplifieradjusted to this sensor.

Problem definition

1130

A 3

B 4.2

B 4.6

5 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

Fig. 3/1: Measuring bridge amplifier


A-19

a) Construct a quarter-bridge using the upper strain gauge of the deflectingarm force sensor.

Exercise

b) Carry out a zero-balance of the bridge amplifier.

c) Press down the deflecting arm lightly and measure the qualitative signalchange at the output of the amplifier.

d) Calculate the amplifier output voltage VO of a quarter-bridge circuit with a

resistance change ∆RSG of approx. 0.2 Ohm. The bridge voltage VE is 5 V.


1130

A 3


A-20

The upper strain gauge of the deflecting arm is connected as resistor R1 to thelefthand branch of the bridge. The remaining resistors of the Wheatstonebridge circuit are connected as fixed resistors


1130

A 3

+

_

Cx

A CO MA/ mA

!

10A

u

!

400 mAMA X

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

1

2

3

5 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

BK BK


Comp.Ref. No.



2 1 Measuring bridge amplifier D.ER-BV-FP1130


4 Plug-in adapter D.MP-B-ME-AS



A-21

The Wheatstone bridge is supplied with 5 V D.C. This voltage is created viathe measuring bridge amplifier from an operating voltage of 24 V D.C.

Note

1130

A 3

R 2

34

0 V

RR

+24V

R 1

2 4 V

5 V

V



A-22

If, in the no-load condition, the bridge is not showing 0 Volts, a zero-balancemust be carried out. In order to do this, the deflecting arm is to remain unloa-ded. The amplifier output voltage is set at 0 Volts with the help of the adjust-ment potentiometer.Because of the sensitivity of the strain gauge and the bridge amplifier a zero-balance to within an accuracy of 10 millivolt is sufficient at the amplifier output.

Part exercise b)

The reason for the bridge signal voltage deviating from 0 V is the minor devia-tions of the individual bridge resistors (strain gauge and fixed resistors) fromthe nominal resistance value.Even in the case of very accurately manufactured resistors, there is a fluctuati-on of a few tenths of a percent. The signal voltage resulting from this in thebridge circuit is also very minor. Due to the large signal amplification, this de-viation from the zero point can be clearly seen.

Note

1130

A 3

+

_

Cx

A COMA/mA

!

10A

u

!

400mAMA X

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DA TA HOLD

PEAK HOLD

DC.. ....

AC

A U TO

RANGE

_+

0 10 20 30 40

D C

V

0 V

IN+

IN-

OUT+

Offset

0 V

OUT-

Fig. 3/4: Zero balance


A-23

• Press down lightly on the deflecting arm using your finger. Make sure thatthe force applied is not excessive, as deformation of the deflecting armmust only occur within its elastic range.

Part exercise c)

• Record the qualitative signal change at the output of the amplifier intable 3/2 of the worksheet.

• Calculate the amplifier output voltage VO. Enter the value in table 3/3 of theworksheet.

Part exercise d)

The amplifier output voltage VO is calculated as follows:

VO = a ⋅ VE ⋅ 0.25 ⋅ ∆ RSGRSG

in Volt

a = Amplification factor of the measuring bridge amplifier

VE = Bridge voltage (5 V)

∆RSG = Resistance change of the strain gauge (hypothetical value 0.2 Ohm)

RSG = Resistance of the unloaded strain gauge (350 Ohm)

• Use the amplification factor a of the measuring bridge amplifier from thecorresponding data sheet in Section D. Enter the value in table 3/3 of theworksheet.

1130

A 3

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

F

5 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

BK BK

+

_

Cx

A COMA/mA

!

10A

u

!

400mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nFFu

AuTTL



A-24

Notes

1130

A 3


The signal change on the amplifier output occurs in the:

Millivolt range

Volt range

Table 3/2: Qualitative signal change

Amplification factor a = _________________

Amplifier output voltage Vo = _________________Volt

Table 3/3: Amplifier output voltage

A-25


A 3

A-26


Calibration of a force sensor using a quarter-bridge circuit Title

To learn about a force sensor using a quarter-bridge as an evaluation circuit.Calibration and commissioning of the unit. Calibration is carried out by meansof various weights.

Learning content

If the dimensions of the deflecting arm, the modulus of elasticity of the deflec-ting arm material, the k-factor of the strain gauge and the amplification of themeasuring amplifier are known, these may be applied in a formula for conversi-on between weight and voltage signal. However, it is easier to calibrate themeasuring unit using known weights. Because of the linear correlation betweenweight and voltage signal, the points determined from the calibration may bejointed by a straight line. Unknown weights can be determined from the voltagesignal with the help of the calibration line.

Technical knowledge

Unknown forces (due to weight) are to be determined using a deflecting armforce sensor with a signal evaluation constructed by means of a quarter-bridgecircuit. In order to determine the characteristic curve, the force sensor must becalibrated beforehand.

Problem definition

1) Strain gauge 2) Amplifier 3) Characteristic curve

1130

A 4

B 4.10

B 4.2

Fig. 4/1: Signal generation and evaluation


A-27

a) Carry out the calibration of the deflecting arm force sensor D.ER-BB-KS-FP1130 using the set of weights D.AS-GWS. The evaluation circuit is con-structed in the form of a quarter-bridge with the upper strain gauge.Draw the characteristic curve of the deflecting arm force sensor.

Exercise

b) Use the characteristic curve to determine an unknown force due to a givenmass.

Please observe the user notes in the introduction section. Appropriate informa-tion regarding connection method and additional technical data can be found inthe corresponding data sheets in the appendix.

1130

A 4


A-28


1130

A 4

+

_

Cx

A CO MA/ mA

!

10A

u

!

400 mAMA X

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

1

2

3

5 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

BK BK


Comp.Ref. No.








A-29

On completion of the quarter-bridge circuit the deflecting arm force sensor re-mains unloaded. The amplifier output voltage is set by turning the alignmentpotentiometer to zero Volts.Because of the sensitivity of the strain gauges and the bridge amplifier a zero-balance to within an accuracy of 10 millivolt is sufficient at the amplifier output.

Zero-balance

1130

A 4

R 2

34

0 V

RR

+24V

R 1

2 4 V

5 V

V


B 4.6


A-30

The deflecting arm is loaded with weights from the set of weights D.AS-GWSranging between 0 to 500 grammes (approx. 0..5 N) in stages of 20, 50, ...,grammes.

Procedure in respect of ca-libration

• Attach the weights separately to the deflecting arm. Enter the amplifier out-put voltage for each weight in table 4/3 of the worksheet.

• Transfer the measured values from table 4/3 to the diagram (fig. 4/5) on theworksheet and draw the characteristic curve of the force sensor for thequarter-bridge.

1130

A 4

+

_

Cx

A COMA/ mA

!

10A

u

!

400 mAMA X

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

D C

V

1

2

3

45 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

BKBK


Comp.Ref. No.



2 1 Set of weights D.ER-GWS





A-31

• Attach a mass (≤500 grammes) to the deflecting arm.Part exercise b)

• Enter the voltage signal in table 4/4 on the worksheet.

• Determine the force on the basis of the characteristic curve (fig. 4/5).

1130

A 4


A-32

Voltage (V) Weight force (N) Load (g)

Table 4/4: Determining the force of a load

Load (g) Weight force (N) Voltage (V)

0 0.0

20 0.2

50 0.5

100 1.0

200 2.0

500 5.0

Table 4/3: Truth table for characteristic curve of sensor

1 2 3 4 50

1

2

F

V

N

V

Fig. 4/5: Diagram for characteristic curve of deflecting arm force sensor inQuarter-bridge circuit


A 4

A-33

Notes


A 4

A-34


Calibration of a force sensor using a half-bridge circuit Titel

To learn about a force sensor using a half-bridge as an evaluation circuit.Calibrating and commissioning of the configuration. Determining the forces.

Learning content

In the half-bridge circuit the resistance changes of the two strain gauges aresubtracted in the adjacent branches of the bridge. Both strain gauges, how-ever, emit opposing signals so that total amounts are added and the signal isamplified in comparison to that of the quarter-bridge circuit. Signals in thesame direction from the two strain gauges, e.g. derived from the interferenceeffects of temperature changes, cancel each other out.

Technical knowledge

Unknown forces are to be determined using a deflecting arm force sensor, withsignal evaluation by means of a half-bridge circuit. In order to determine thecharacteristic curve, a calibration of the force sensor must be carried out be-forehand.

Problem definition

1130

A 5

B 4.3

B 4.2

F F

V V

Quarter bridge Half-bridge

Fig. 5/1: Characteristic curve difference


A-35

a) Construct the evaluation circuit of the deflecting arm force sensor in theform of a half-bridge.Carry out a zero-balance.

Exercise

b) Calibrate the deflecting arm force sensor D.ER-BB-KS-FP1130 using theset of weights D.AS-GWS.Draw the characteristic curve of the deflecting arm force sensor.

c) Use the characteristic curve to determine the unknown force of a givenmass.


1130

A 5


A-36

The two strain gauges of the deflecting arm force sensor are connected to thelefthand branch of the bridge as R1 and R4. The remaining resistors R2 andR3 of the Wheatstone bridge circuit are fixed resistors.


1130

A 5

+

_

Cx

A COMA/ mA

!

10A

u

!

400 mAMA X

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

A C

AUTO

RANGE

_+

0 10 20 30 40

DC

V

1

2

35 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

BKBK

WH

WH


Comp.Ref. No.








A-37

On completion of the half-bridge circuit, the deflecting arm force sensor re-mains unloaded. The amplifier output voltage is set by turning the alignmentpotentiometer to zero Volts.Because of the sensitivity of the strain gauges and the bridge amplifier, a zero-balance to within an accuracy of 10 millivolt is sufficient at the amplifier output.

Zero-balance

1130

A 5

R 2

34

0 V

RR

+24V

R 1

2 4 V

5 V

V



A-38

The deflecting arm is loaded with weights from the set of weights D.AS-GWSranging from 0 to 500 grammes (0..5 N) in steps of 20, 50, ..., grammes.

Part exercise b)

• Attach the weights individually to the deflecting arm. Enter the amplifier out-put voltage for each weight in table 5/3 of the worksheet.

• Transfer the measured value from table 5/3 to diagram Fig. 5/5 on theworksheet and draw the characteristic curve of the force sensor for thehalf-bridge.

Compare the characteristic curve of the half-bridge circuit with the quarter-bridge circuit from exercise 4 and describe the difference. What is their effecton the signal resolution?

Question

1130

A 5

+

_

Cx

A COMA/mA

!

10A

u

!

400mAMAX

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

1

2

3

45 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

BKBK

WH

WH


Comp.Ref. No.



2 1 Set of weights D.ER-GWS






A-39

• Without prior knowledge of the resulting force, attach a mass (≤500 gram), tothe deflecting arm. In order to be able to make a direct comparison withexercise 4, the use of the same part is recommended for the weight meas-urement.

• Enter the signal voltage in table 5/4 of the worksheet.

• Determine the force from the characteristic curve (Fig. 5/5).

How large is the signal difference, when using the same mass in exercise 4and 5 ?

Question

Part exercise c)

1130

A 5


A-40

1130

A 5


Voltage (V) Weight force (N) Load (g)

Table 5/4: Determining the force of a load

Load (g) Weight force (N) Voltage (V)

0 0.0

20 0.2

50 0.5

100 1.0

200 2.0

500 5.0


1 2 3 4 50

1

2

F

V

N

V

Fig. 5/5: Diagram for characteristic curve of deflecting arm force sensor inHalf-bridge circuit

A-41

AnswerPart exercise b)

AnswerPart exercise c)


A 5

A-42


Calibration of an industrial force sensor Title

Construction, connection and calibration of an industrial force sensor for thedirect measurement of larger forces.

Learning content

Industrial force sensors contain a full-bridge circuit. With this design, the auxili-ary circuit in the form of fixed resistors is not required. The internal full-bridgecircuit is complemented by means of temperature-dependent resistors andtrimmed fixed resistors. With this type of circuit, which is largely independent oftemperature, a good linear characteristic is achieved.

Technical knowledge

An industrial force sensor is used for the measurement of larger forces. Thecharacteristic curve of this force sensor is to be determined by means of cali-bration.

Problem definition

1130

A 6

F

1) Force sensor 2) Amplifier 3) Characteristic curve

Fig. 6/1: Force sensor

B 4.5

B 5.1


A-43

a) Connect the force sensor D.ER-KS-FP1130 to the measuring bridge ampli-fier D.ER-BV-FP1130.Place the weight support D.AS-SGA on to the force sensor through theupper hole of the hollow profile.Carry out a zero-balance.

Exercise

b) Carry out a calibration of the force sensor using the set of round weightsD.AS-S-GWS.Draw the characteristic curve of the force sensor.


1130

A 6


A-44

The force sensor D.ER-KS-FP1130 contains a full Wheatstone bridge circuitfor signal generation. Connection is established with the help of a measuringbridge amplifier D.ER-BV-FP1130 to the bridge supply voltage and the ampli-fier input. Additional fixed resistors for the bridge are not required.


1130

A 6

+

_

Cx

A COMA/ mA

!

10A

u

!

400 mAMA X

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

D C

V

23

5 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

1

WH / BK

BN / BK

YE / WH

GN / WH


Comp.Ref. No.


1 1 Force sensor D.ER-KS-FP1130






A-45

The unit enclosed by a broken line in the electrical circuit diagram denotes thefull bridge in the force sensor.

• Place the weight support D.AS-SGA on to the force sensor through theupper hole of the hollow profile. The amplifier output voltage is set by tur-ning the alignment potentiometer to zero Volt.Because of the sensitivity of the strain gauges and the bridge amplifier, azero-balance to within a 10 millivolt accuracy is sufficent at the amplifieroutput.

Zero-balance

1130

A 6

R 2

34

0 V

RR

+24V

R 1

2 4 V

5 V

V



A-46

Part exercise b)

1130

A 6

+

_

Cx

A COMA/mA

!

10A

u

!

400mAMA X

500 V MAX

!

750V1000V.....

V

TTL

OFF

A

mAmV

V

nFFu

AuTTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

2

3

5 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

WH / BK

BN / BK

YE / WH

GN / WH

1

45


Comp.Ref. No.



2 1 Weight support D.AS-SGA

3 1 Set of round weights D.AS-S-GWS-FP1130






A-47

• Arrange the circular weights D.AS-S-GWS (1 kg each) in a stack on theweight support D.AS-SGA.

Make sure that the force sensor is mounted firmly on the profile plate and thatthe stack of disc weights rests securely on the force sensor. Injury can becaused by dropping disc weights.

Note

• Determine the signal at the amplifier output for each additional weight pla-ced on the support.

• Enter the individual measured values in table 6/3 of the worksheet.

• Transfer the values from table 6/3 to the diagram (fig. 6/5) of the worksheetand draw the characteristic curve of the force sensor.

Only the lower range of the characteristic curve is established (up to 100 N) bymeans of the 100 N weight set. The characteristic curve can be extended tothe upper range (up to 200 N) on the basis of the linearity.When determining the characteristic curve of the force sensor, the inherentweight of the weight support D.AS-SGA is not taken into account, as the zero-balance was carried out with the weight support attached.

Note

1130

A 6


A-48

Notes

1130

A 6


Load (kg) Weight force (N) Voltage (V)

0 0

1 10

2 20

3 30

4 40

5 50

6 60

7 70

8 80

9 90

10 100


0 2 0 4 0 6 0 8 0 10 0 1 2 0 1 4 0 16 0 2 0 0N

F

1.60

V

2.00

1.40

1.20

1.00

0.80

0.60

0.40

0.20

1.80

2.40

V

Fig. 6/5: Diagram for characteristic curve of force sensor

A-49


A 6

A-50


Force measurement on pneumatic cylinders using an industrial force sensor Title

Detecting the force of a piston rod and the friction forces of a pneumatic cylin-der using a force sensor.

Learning content

The effect of force on the piston surface of a pneumatic cylinder can be calcu-lated from the pneumatic pressure and the area of the piston surface. Theforce on the piston rod is reduced by the friction force of the piston.

Technical knowledge

In order to determine the piston rod and friction forces of a pneumatic cylindera configuration is used whereby, inside a hollow profile, the piston rod of thecylinder presses directly on to a force sensor. These forces are to be deter-mined by means of the force sensor.

Problem definition

1130

A 7

B 4.5

p

Fp2

1Fp

Signal Sig

nal

Fig. 7/1: Force measurement using a pneumatic cylinder

1) Force sensor 2) Cylinder


A-51

Prior knowledge of handling and connection technology regarding analoguepressure sensors is essential to carry out this exercise. This can be obtainedfrom the corresponding data sheets in the appendiix as well as from exercisesA 8 and A 9.

Note

a) Connect the sensor unit D.ER-KS-FP1130 to the double-acting cylinderD.AS-DSN-PPV as follows:- pneumatically to the service unit D.ER-FRC-1/8-S- electrically to the bridge amplifier D.ER-BV-FP1130- Use the analogue pressure sensor D.ER-SDE-10-10V/20mA in

conjunction with the connection plate D.ER-AE-101AF and thedigital multimeter D.AS-DMM to detect the pressure on the pistonside of the cylinder.

Exercise

b) Calculate the theoretical cylinder force for the advance movement at pres-sure values of 1 bar, 2 bar, 3 bar and 4 bar.

c) Measure the actual force of the piston rod at the pressure values used inpart exercise b).

d) Calculate the friction force for each measuring point.

Please observe the user notes in the introduction section when carrying outthese exercises. Appropriate information regarding connection method and ad-ditional technical data can be found in the corresponding data sheets in theappendix.

1130

A 7


A-52


1130

A 7

13

2S

DE

-...

4

5

Fig. 7/2: Pneumatic connection

Comp.Ref. No.


1 1 Service unit D.ER-FRC-1/8-S


3 1 Pressure manifold D.ER-FR-4-1/8-B

4 1 Cylinder D.AS-DSN-PPV





A-53

A certain air pressure is set at the service unit and acts on the piston side ofthe cylinder chamber. This pressure is measured by the analogue pressuresensor connected in parallel and can be read on the multimeter.

The signal is created in the force sensor by means of strain gauges, which areconnected in the form of a full bridge. The use of fixed resistors on the bridgeamplifier is therefore not required. The pressure on the piston side of the cylin-der chamber is detected by means of the analogue pressure sensor D.ER-SDE-10-10V/20mA and the multimeter.

1130

A 7

P

10V/20mA

Fig. 7/3: Pneumatic circuit diagram

B 2.5


A-54

• Connect the force sensor to the measuring bridge amplifier

• Connect the voltage signal of the pressure sensor to VI0 at INPUT 0 at thetop and the current signal to II0 at INPUT 0 at the bottom of the connectionplate D.ER-AE-101AF. Connect 0 V to GND.The signal switching unit is set at 0 position.The voltage signal is connected to the digital multimeter via OUTPUT 0.

1130

A 7

24V24V

0V 0V

0V

0V

GND

GND

24V

INPUT

OUTPUT

INPUT

+

_

Cx

A COMA/mA

!10A

u

!40 0mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

n F

Fu

Au

TTL

DATA HOL D

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

10V/20mA

0 1 2 3

0 1 2 3

0 1

RD

BU

BK

1

SDE-. . .

+

_

Cx

A CO MA/mA!

10A

u

!400 mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nF

Fu

Au

TTL

DATA HOL D

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

2

5

4 3

5

5 V

24 V

0 V

IN+

IN-

OUT+

Offset

24 V

0 V

OUT-

WH / BK

BN / BK

YE / WH

GN / WH

60

23

1

WH



A-55

The unit enclosed by a broken line is the full bridge as constructed in the forcesensor.

When the electrical circuit has been constructed, the sensor remains unloaded.The amplifier output voltage is set by turning the alignment potentiometer tozero Volts.

Zero-balance

Because of the sensitivity of the strain gauges and the bridge amplifier, a zero-balance to within an accuracy of 10 millivolt is sufficient at the amplifier output.

1130

A 7

Comp.Ref. No.





4 1 Adapter plate D.ER-AE-101AF





R

3

0 V

RR

+ 24 V

R 1 2

4

RD( 1)

BK(3 )

WH( 4)

BU(2 )

P

24V

5 V

V



A-56

Part exercise b)

The piston diameter d of the cylinder is 25 mm.

1 bar = 0.1 N/mm2

• Carry out the calculation according to the above formula. Enter the numeri-cal values in table 7/3 of the worksheet.

• Set the pressure on the service unit for each measuring point. Take a rea-ding of the precise pressure value on the multimeter.

Part exercise c)

The voltage signal of the analogue pressure sensor D.ER-SDE-10-10V/20mAcorresponds to the measured pressure value in bar. The voltage signal readcan therefore be entered in the table without prior conversion.

Note

• Enter the voltage signal for each measuring point in table 7/3 on theworksheet.

• Take the cylinder force (Fact) for each measuring point from the charac-teristic curve established in exercise 6. Enter the values in table 7/3 on theworksheet.

• Calculate the friction forces for each measuring point. Enter the calculatedfriction force also in table 7/3 of the worksheet.

Part exercise d)

Friction force

1130

A 7

The theoretical force (Ftheor) is calculated from the pressure across the pi-ston area.

Ftheor =p ⋅ A

Ftheor = theoretical force in N (N = Newton)p = Pressure in N/mm 2

A = Area = π /4 ⋅ d 2 in mm 2.

B 1.7

The friction force (FF) is the difference between the theoretical force (Ftheor)and the actual cylinder force (Fact).

FF = Ftheor - Fact


A-57

Festo Didactic1130

A 7

A-58


A 7

Pressure(bar)

Ftheor (N) Voltage (V) Fact. (N) FF (N)

1.0

2.0

3.0

4.0

Table 7/3: Truth table for determining cylinder force

A-59

Notes

1130

A 7


A-60


Commissioning of an analogue pressure sensor Title

To learn about the pneumatic and electrical connection of an analogue pressu-re sensor.

Learning content

The analogue pressure sensors contained in the equipment set are piezoresi-stive pressure sensors. Apart from the pressure detector with built-in semicon-ductor strain gauges in the form of a full bridge circuit, these include a measu-ring amplifier which supplies both a voltage signal (0 ... 10 V) as well as acurrent signal (0 ... 20 mA) for the specified pressure measuring range. Bothsignals are available simultaneously.

Technical knowledge

For proper functioning, the analogue pressure sensor must be connected cor-rectly both electrically and pneumatically and operated within the permissiblepressure and voltage ranges. Its pneumatic and electrical characteristics are tobe examined.

Problem definition

1130

A 8

B 7.4

p

SDE-...

Fig. 8/1: Analogue pressure sensor


A-61

a) Using the data sheet, identify the individual electrical connections of theSDE-... series analogue pressure sensor according to the plug colours.

Exercise

b) Connect the analogue pressure sensor D.ER-SDE-10-10V/20mA as follows:- pneumatically via the pressure manifold D.ER-FR-4-1/8-B to the service-

unit D.ER-FRC-1/8-S- electrically via the connection plate D.ER-AE-101AF to the voltage

supply and the multimeter D.AS-DMM.

Please observe the user notes in the introduction section when carrying outthese exercises. Appropriate information regarding connection method and ad-ditional technical data can be found in the corresponding data sheets in theappendix.

1130

A 8


A-62

Connection and plug colour can be matched up with the help of the datasheet. Please follow this information.


• Enter the data in table 8/3 on the worksheet.

Part exercise b)

1130

A 8

1

3

2

SD

E-.

..

bar0

10

20

3 0

40


Comp.Ref. No.








A-63

It is important to ensure that the pneumatic supply line to the sensor is asshort as possible, i.e. the sensor should be near the point in the pneumaticcircuit, where the air pressure is to be measured. Due to lengthy columns of airin the lines, the measurement of pressure change is subject to a time delay.

Note

1130

A 8

P

10V/20mA



A-64

The broken lines indicate that with only one multimeter, current and voltagemeasurements cannot be carried out simultaneously.

1130

A 8

24V 24V

0V 0V

0V

0V

GND

GND

24V

INPUT

OUTPUT

INPUT

+

_

Cx

A COMA/mA!

10A

u

!400mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nF

Fu

Au

TTL

DATA HOLD

P EA K HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

10V/20mA

0 1 2 3

0 1 2 3

0 1

RD

BK

BU

WH

2

4

3

1

SDE-. . .

0

23

1


Comp.Ref. No.



2 1 Connection unit D.ER-AE-101AF






A-65

The analogue pressure sensor D.ER-SDE-10-10V/20mA is connected to thevoltage supply and the multimeter via the connection unit D.ER-AE-101AF.The voltage signal is connected to input 0 of the upper row of sockets and thecurrent signal to input 0 of the lower row of sockets. The multimeter is connec-ted to that connection unit corresponding to the `voltage’ or `current’ measure-ment:– Voltage signal to output 0– Current signal to output 1– The signal switching unit is set at 0

1130

A 8

0 V

P

+ 2 4 V

RD( 1)

BK( 3)

WH(4)BU( 2)

V



A-66

1130

A 8


Connection Plug colour

+ 24 V

0 V

Signal V

Signal I

Table 8/3: Plug colours

A-67

Notes

1130

A 8


A-68


Characteristic curve of an analogue pressure sensor Title

To learn about the behaviour of an analogue pressure sensor by means ofmeasuring and comparing the voltage and current characteristic curves andcarrying out pressure measurements.

Learning content

There are analogue pressure sensors, which have a characteristic curve with azero offset. The zero offset can be detected by calibrating the pressure sensorD.ER-SDE-10-5V/20mA against a reference pressure sensor D.ER-SDE-10-10V/20mA. The purpose of the zero offset, or zero signal, is to check thefunctionality of the sensor and the connected measuring amplifier, particularlyin automated systems. An analogue pressure sensor generates an electricalsignal, which is proportional to the pressure being measured. With the help ofa characteristic curve pertaining to a pressure sensor, it is possible to determi-ne unknown pressure values very accurately and at any point.

Technical knowledge

With the help of the known characteristic curve of an analogue pressure sen-sor the voltage and current characteristic curves of a second analogue pressu-re sensor are to be established. The newly established characteristic curvesare to be used for determining air pressure.

Problem definition

1130

A 9

B 4.7

p

?p

p SDE-. . .

SDE-. . .

p10 V/20 mA

5V/20mA

V ,

V,

Fig. 9/1: Characteristic curves of various analogue pressure sensors


A-69

a) Connect the pressure sensor D.ER-SDE-10-5V/20mA as follows:– pneumatically in parallel with the D.ER.SDE-10-10V/20mA to the

compressed air supply– electrically to the connection plate D.ER-AE-101AFIn part exercises b) and c), the analogue pressure sensor D.ER-SDE-10-10V/20mA is the reference pressure sensor.

Exercise

b) Determine the voltage characteristic curve of the analogue pressure sen-sorD.ER-SDE-10-5V/20mA.

c) Determine the current characteristic curve of the analogue pressure sensorD.ER-SDE-10-5V/20mA.

d) Set the service unit at any pressure. Determine the exact pressure valuefrom the characteristic curves of the analogue pressure sensor D.ER-SDE-10-5V/20mA established in b) and c).

Please observe the user notes in the introduction section when carrying outthe exercises. Appropriate information regarding connection method and addi-tional technical data can be found in the corresponding data sheets im theappendix.

1130

A 9


A-70

The two analogue pressure sensors are connected in parallel to the serviceunit via the pressure manifold D.ER-FR-4-1/8-B.


1130

A 9

ba r0

10

20

30

4 0

1 2

43

SD

E-...

SD

E-...


Comp.Ref. No.









A-71

1130

A 9

P

5V/20mA

10V/20mA



A-72

The analogue pressure sensor D.ER-SDE-10-5V/20mA is connected to thevoltage supply and the multimeter via the connection plate D.ER-AE-101AF.

The broken lines indicate that with one multimeter only, voltage and currentmeasurements cannot be carried out simultaneously.

1130

A 9

24V 24V

0V 0V

0V

0V

GND

GND

24V

INPUT

OUTPUT

INPUT

+

_

Cx

A COMA/mA!

10A

u

!400mAMA X

500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nF

Fu

Au

TTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

10V/20mA

0 1 2 3

0 1 2 3

0 1

RD

BK

BU

WH

2

4

3

1

5V/20mA

5

SDE-. . .

SDE-. . .

0

23

1

BK

Fig. 9/4:d Electrical connection

Comp.Ref. No.





4 1 Connection unit D.ER-AE-101AF





A-73

1130

A 9

0 V

P

+24V

P

RD (1 )

BK(3)

WH (4 )

BU(2) BU(2)WH (4 )

BK(3)

RD(1)

V



A-74

In order to determine the sensor characteristic curve of the analogue pressuresensor D.ER-SDE-10-5V/20mA, the pressure at the individual measuringpoints must be known. To achieve this, the analogue pressure sensor D.ER-SDE-10-10V/20mA is used as a reference sensor. With this reference sensor,the voltage signal in Volts corresponds to the measured pressure in bar.

Reference sensor

Example: Voltage signal 2 V ==> pressure 2 bar

1130

A 9

1 V

1 ba r

ba rp

V

1

2

3

4

5

1 2 3 4 5

V

Fig. 9/6: Voltage characteristic curve of reference pressure sensorD.ER-SDE-10-10V/20mA

B4.10


A-75

The multimeter is set for ‘voltage measurement’ and at a measuring rangewhich detects the anticipated voltage (in this instance: from 0 to 10 Volt). Plea-se observe the operating instructions for the multimeter.

Part exercise b)

• Increase the pressure on the service unit from 0 bar to the system pressurein stages of 0.5 bar, whilst alternately switching the voltage signals of thetwo pressure sensors to the multimeter via the signal switching unit.

• Enter the voltage determined in respect of each measuring point in table9/3 of the worksheet.

• Transfer the points to the diagram (Fig. 9/7) of the worksheet and draw thevoltage characteristic curve.

1130

A 9


A-76

The multimeter is switched to `current measurement’ and possibly (dependingon the multimeter) to a measuring range, which will detect the current anticipa-ted (in this instance: from 0 to 20 mA).

Part exercise c)

• Increase the measuring pressure on the service unit from 0 bar to the sy-stem pressure in stages of 0.5 bar, whilst alternately switching the signalsof the two pressure sensors to the multimeter via the signal changeoverswitch.

The connection cable on the multimeter between the voltage and current inputmust be exchanged for each measuring point. It is also possible to use twomultimeters.

Note

• Enter the established current value for each measuring point in table 9/4 ofthe worksheet.

• Transfer the points in the diagram (fig. 9/8) of the worksheet and draw thecurrent characteristic curve.

• Set the service unit at any pressure observing only the pressure gauge ofthe service unit while doing this.

Part exercise d)

• Now determine the voltage and current signal with the help of the analoguepressure sensor D.ER-SDE-10-5V/20mA and the multimeter and enter the-se values in table 9/5.

• Take a reading of the pressure values in respect of each signal from thecharacteristic curves defined under b) and c). Enter these values in table9/5 on the worksheet.

1130

A 9


A-77

Festo Didactic1130

A 9

A-78


p (bar) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Voltage (V)

Table 9/3: Truth table for voltage characteristic curve

1 2 3 4 6

4

0

1

2

3

V

p

bar

V

Fig. 9/7: Diagram for voltage characteristic curve

1130

A 9

A-79


Measuring device Voltage (V) Current (mA) Pressure (bar)

Pressure gauge ————— —————

SDE-10-10V/20mA —————

SDE-10-5V/20mA —————

SDE-10-5V/20mA —————

Table 9/5: Pressure measurement

1 2 3 4 60

p

bar

mA

16

12

8

4

Fig. 9/8: Diagram for current characteristic curve

1130

A 9

p (bar) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

I (mA)

Table 9/4: Truth table for current characteristic curve

A-80


Setting of a mechanical pressure switch Title

Knowledge regarding the setting, checking and use of mechanical pressureswitches.

Learning content

In the pressure switch D.ER-PEV-1/4-B, a mechanical microswitch is actuatedby the diaphragm of the pressure sensor. This binary output signal can beprocessed directly via display units or controllers. The switch-on pressure du-ring increasing pressure is higher than the reset pressure during falling pressu-re. The difference is described as hysteresis. Pressure switches are usedmainly for the purpose of pressure monitoring in pneumatic systems. Theytrigger an electrical signal if a predetermined pressure value is exceeded orfails to be maintained.

Technical knowledge

The mechanical and electrical characteristics of a mechanical pressure switchare to be examined with the help of an analogue pressure sensor.

Problem definition

1130

A 10

B 7.2

p

t

t t0

1

SDE- ...

V,

Analogue signal Binary signal

Pressure characteristic

Fig. 10/1: Comparison of analogue and binary pressure switch signal


A-81

a) Connect the mechanical pressure switch D.ER-PEV-1/4-B pneumaticallyand electrically so that its switching point can be determined and set withthe help of the analogue pressure sensor D.ER-SDE-10-10V/20mA.

Exercise

b) Determine the actual switching point set for the increasing air pressure withthe help of the analogue pressure sensor D.ER-SDE-10-10V/20mA.

c) Set the pressure switch D.ER-PEV-1/4-B during increasing pressure at avalue of 3 bar. Check the setting you have made.

d) Measure the hysteresis of the pressure sensor for the setting carried outunder c).

e) Repeat points c) and d) for response pressures of 1 bar, 2 bar and 4 bar.

Please observe the user notes in the introduction part when carrying out theexercises. Appropriate information regarding connection method and additionaltechnical data can be found in the corresponding data sheets in the appendix.

1130

A 10


A-82

The pressure switch D.ER-PEV-1/4-B is connected in parallel with the analo-gue pressure sensor D.ER-SDE-10-10V/20mA via the pressure manifold D.ER-FR-4-1/8-V/20mA.


1130

A 10

12

43

SD

E-.

..

ba r0

10

20

30

40


Comp.Ref. No.









A-83

1130

A 10

P

10V/20mA



A-84

1130

A 10

24V 24V

0V 0V

0V

0V

GND

GND

24V

INPUT

OUTPUT

INPUT

+ 24 V

+ 24 V

+ 24 V

+ 24 V

0 V0 V

0 V 0 V

+

_

Cx

A COMA/mA!

10A

u

!400mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nF

Fu

Au

TTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

10V/20mA

RD

BK

BU

WH

RD

BK

WH

12

34

5

6

SDE-. . .

0

23

1


Comp.Ref. No.



2 1 Distribution plate D.ER-VERT-SENSOR



5 1 Signal switching unit D.ER-SUAE-101





A-85

• Connect the pressure sensor to the binary distribution plateD.ER-VERT-SENSOR. This enables you to determine the switching statusof the pressure switch. If a buzzer sounds, the pressure switch is in theswitched status.

The pressure switch D.ER-PEV-1/4-B consists of a mechanical switch, whichcan be used both as a normally closed contact and a normally open contact.The signal voltage is switched direct to the buzzer of the distribution unit viathis switching contact.

• By manual adjustment, slowly increase the pressure on the service unit. Atthe same time, the display of the multimeter must be observed. If the pres-sure switch is actuated, the buzzer of the distribution unit sounds. At thispoint (po) the manual pressure increase on the service unit is stopped im-mediately. The response pressure can be read on the multimeter.

Part exercise b)

• Enter the measured values in table 10/3 of the worksheet.

• Often, it is not possible to stop the pressure increase as soon as the re-sponse pressure has been reached. In order to avoid errors, it is recom-mended to repeat the measuring procedure as many times as required untila consistent value is achieved.

If the setting of the pressure switch is in a high pressure range, which is notreached when the pressure on the service unit is increased (pressure switchnot switching), the following rough presetting is recommended:

Note

1) Turn the adjusting screw to the lefthand stop2) Turn the adjusting screw three revolutions to the right.

1130

A 10

0 V

P

+ 2 4 V

PRD( 1)

BK( 3)

WH(4)

BU(2)

RD(1)

BK(4)WH(2)

V



A-86

• The system pressure is set at 3 bar on the service unit. This enables theexact pressure value to be read on the multimeter with the help of theanalogue pressure sensor D.ER-SDE-10-10V/20mA.

Part exercise c)

During the setting of the pressure on the service unit, it is possible for a slightreduction in pressure to occur after the lines and pressure manifold have beencharged. In this case, the setting on the service unit must be adjusted until thepressure becomes stable.

Note

• If the pressure switch has already switched, then the adjusting screw mustbe turned to the right by means of a screw driver until the switching con-tacts open.

• The setting can now begin. To do this, the adjusting screw is turned slowlyto the left until the pressure switch switches. If the switching point is re-ached, a buzzer will sound.

The new setting of the pressure switch is checked in accordance with themethod used in part exercise b).

Checking

1130

A 10


A-87

The differential pressure is known as the hysteresis of a pressure switch,which occurs between the switch-on point for increasing pressure po and theswitch-off point for falling pressure pu. The extent of the hysteresis in this caseis dependent on the actual setting of the pressure switch.

Part exercise d)

• The pressure of the actuated pressure switch is reduced slowly at the ser-vice unit until the pressure switch switches off. At this point, the reduction ofpressure must be stopped immediately.Parallel to the measurement of the switch-on pressure, the switch-off pres-sure is determined by means of the analogue pressure sensor D.ER-SDE-10-10V/20mA and the multimeter and entered in table 10/4 of theworksheet.The hysteresis is calculated as follows:

• Repeat the hysteresis measurements for switch-on pressures of 1 bar, 2bar and 4 bar.Enter the values in table 10/5 of the worksheet.

Part exercise e)

• The hysteresis measurement is carried out as in part exercise d)

1130

A 10

Hysteresis = Switch-on pressure (po) - Switch-off pressure (pu)


A-88

Worksheet Didactic1130

A 10

Measurement Response pressure (bar)

1

2

3

4

Table 10/3: Truth table for determining response pressure

Measurement po (bar) pu (bar) Hysteresis (bar)

1

2

3

4

Table 10/4: Truth table for determining hysteresis

po (bar) pu (bar) Hysteresis (bar)

1.00

2.00

3.00

4.00

Table 10/5: Hysteresis for various switching states

A-89

Notes


A 10

A-90


Setting of an electronic pressure switch Title

A pneumatic-electronic switch is operated as a pressure switch. Learning content

The electronic pressure switch D.ER-PEN-M5, also known as a pneumatic-electronic switch, fulfills the function of the differential pressure switch. Theposition of a metal bellows varies depending on the differential pressure and ismeasured with the help of an inductive proximity switch. By pre-loading thebellows using an adjustable spring, it is possible to select the pressure swit-ching point. The binary switching signal of the pressure switch D.ER-PEN-M5is bounce-free and can be processed directly in display units or controllers.

Technical knowledge

An electronic pressure switch is to be used for pressure monitoring in a pneu-matic system. For this purpose, the pressure switch is to be set at a specifiedswitching pressure.

Problem definition

1130

A 11

B 7.2

Service unit Electronic pressure switch

Fig. 11/1: Monitoring of pneumatic pressure using a pressure switch


A-91

a) Connect the electronic pressure switch D.ER-PEN-M5 pneumatically andelectronically so that its switching point can be determined and set by me-ans of the analogue pressure sensor D.ER-SDE-10-10V/20mA. The diffe-rential pressure input remains unconnected.

Exercise

b) Determine the actual switching point set for rising air pressure with thehelp of the analogue pressure sensor D.ER-SDE-10-10V/20mA.

c) Set the pressure switch D.ER-PEN-M5 for rising pressure to a switchingpoint of 3 bar.Check the setting you have made.

d) Measure the hysteresis of the pressure switch for the setting carried outunder c).

e) Repeat points c) and d) for response pressures of 1 bar, 2 bar and 4 bar.


1130

A 11


A-92

When using the pneumatic-electronic switch D.ER-PEN-M5 as a pressureswitch, the differential pressure in respect of ambient pressure is measured. Todo this, the signal pressure is connected to port P1. Port P2 remains open, i.e.the differential pressure input is subject to ambient pressure.In order to measure the actual pressure on the pressure switch, the analoguepressure sensor D.ER-SDE-10-10V/20mA is connected parallel to port P1 viathe pressure manifold D.ER-FR-4-1/8-B.


1130

A 11

12

3

SD

E-.

..

bar0

1 0

20

30

40

4


Comp.Ref. No.





4 1 Pneum.-elect. switch D.ER-PEN-M5




A-93

1130

A 11

P

10V/20mA

P

P

1

2



A-94

1130

A 11

24V 24V

0V 0V

0V

0V

GND

GND

24V

INPUT

OUTPUT

INPUT

+ 24 V

+ 24 V

+ 24 V

+ 24 V

0 V0 V

0 V 0 V

+

_

Cx

A COMA/mA!

10A

u

!400mAMAX 500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nF

Fu

Au

TTL

DATA HOLD

PEAK HOLD

DC......

AC

A UTO

RANGE

_+

0 10 20 30 40

DC

V

10V/20mA

RD

BK

BU

WH

RD

BK

1

2

34

5

6

BU

SDE-. . .

0V

GND

24V

0

23

1


Comp.Ref. No.








12 Plug-in connector D.MP-B-ME-AS



A-95

In order to measure the switching status, the pressure switch D.ER-PEN-M5 isconnected to the binary distribution plate D.ER-VERT-SENSOR. When thebuzzer sounds, the pressure switch is in the switched status.

The electronic pressure switch D.ER-PEN-M5 has a signal output, to which theoperating voltage is electronically switched. The pressure switch can only beused as a normally open contact.

• The pressure on signal input P1 is increased slowly until the pressureswitch is actuated. Switching can be observed via both the light emittingdiode (LED) of the pressure switch D.ER-PEN-M5 as well as the sound ofthe buzzer.

Part exercise b)

• The manual pressure increase on the service unit is stopped immediatelyafter switching. The switching point can then be read on the multimeter withthe help of the analogue pressure sensor D.ER-SDE-10-10V/20mA. Carryout the measurements and enter the measured values in table 11/3 on theworksheet.

• There is a danger that the manual pressure increase will not be stopped intime when the switching point is reached. In order to avoid measuring er-rors, it is recommended to repeat the measuring process until several coin-ciding measured values are available.

If the setting of the pressure switch is in a pressure range which is so high thatit is not achieved by increasing the pressure on the service unit (the pressureswitch does not switch), then the following rough presetting is recommended:

Note

1) Turn the adjusting screw to the righthand stop

2) Turn the adjusting screw six revolutions to the left.

1130

A 11

0 V

P

+ 2 4 V

P

P1

2

RD( 1)

BK( 3)

BU( 2)

BU( 3)

BK( 4)

RD( 1)

WH(4)

V



A-96

• The system pressure is set at 3 bar on the service unit whereby the exactpressure value is read on the multimeter with the help of the analoguepressure sensor D.ER-SDE-10-10V/20mA.If the pressure switch D.ER-PEN-M5 is already actuated, then the the adju-sting screw is to be turned to the left by means of a screw driver until theswitch resets.

Part exercise c)

• You can now start the setting by turning the adjusting screw very slowlytowards the right until the pressure switch actuates at switching point po.Immediately upon switching, cease turning the adjusting screw.

Checking of the new pressure switch setting is carried out according to theprocedure used in part exercise b).

Checking

If it is not sufficiently accurate, then the entire setting of the pressure switchmust be repeated using the procedure described.

Hysteresis occurs with an electronic pressure sensor in the same way as itdoes with a mechanical pressure switch.

Part exercise d)

• The actuating pressure applied to the pressure switch is reduced at theservice unit until the pressure switch resets. At the point of resetting, thereduction in pressure must be stopped immediately.

• Parallel to the measurement of the switch-on pressure, the switch-off pres-sure is determined by means of the analogue pressure sensor D.ER-SDE-10-10V/20mA and the multimeter and entered in table 11/4 on theworksheet.

The hysteresis is calculated as follows:

• Repeat the hysteresis measurement for the differential pressures of 1 bar, 2bar and 4 bar. Enter the measured values in table 11/5 on the worksheet.

Part exercise e)

• The hysteresis measurement is carried out in the same way as in partexercise d).

1130

A 11

Hysteresis = Switch-on pressure (po) - Switch-off pressure (pu)


A-97

1130

A 11

Festo Didactic

A-98


A 11


1

2

3

4

Table 11/3: Truth table for determining response pressure


1

2

3

4

Table 11/4: Truth table for determining the hysteresis


1.00

2.00

3.00


A-99

Notes


A 11

A-100


Using an electronic pressure switch as a differential pressure switch Title

A pneumatic-electronic switch is operated as a differential pressure switch. Learning content

Differentiation is made between absolute pressure sensors, relative pressuresensors and differential pressure sensors. Absolute pressure sensors measurepressure against vacuum. The air pressure quoted in meteorologicalbroadcasts is one example of this. Relative pressure sensors measure pressu-re relative to ambient pressure. Absolute pressure sensors and relative pressu-re sensors have one single pressure port. In contrast, differential pressure sen-sors measure the difference in pressure across two pressure ports. If onepressure port of a differential pressure sensor is left open, then the differentialpressure sensor operates identically to a relative pressure sensor. Differentialpressure sensors are available as analogue differential pressure sensors ordifferential pressure switches. Pressure sensor D.ER-PEN-M5 is an example ofa differential pressure switch.

Technical knowledge

The pressure switch D.ER-PEN-M5 is to be used to monitor the contaminationlevel of a filter in a pneumatic system. To do this, the pressure switch must beset to a predetermined differential pressure. The air filter function is simulatedby means of two pressure circuits.

Problem definition

1130

A 12

B 7.1

Filter Differential pressure switch

Fig. 12/1: Monitoring of filter using a differential pressure switch


A-101

a) Carry out the pneumatic connection of pressure sensor D.ER-PEN-M5 insuch a way that an adjustable, static pressure can be connected to pointP2 (see Fig. 12/3).

Exercise

b) Set the pressure at point P1 to 4 bar. A signal should be emitted from thepressure switch, when the pressure drop on the filter is 1 bar. Now set thedifferential pressure at point P2 in order for this condition to be fulfilled.

c) Set the pressure switch at a differential pressure of 1 bar. Check the settingon the pressure switch.

d) Measure the hysteresis of the pressure switch for the setting carried outunder c).

e) Repeat the hysteresis measurement for differential response pressures of3 bar and 2 bar. The system pressure in each case is 4 bar.


1130

A 12


A-102


The pressure on differential pressure input P2 is created statically with the helpof a partly charged compressed air reservoir. The analogue pressure sensor isused for pressure measurement at several points in the pneumatic system,hence the supply lines are denoted by broken lines.

1130

A 12

1

2

2

3

4

5

6

7

SDE-...

ba r0

10

20

30

40


Comp.Ref. No.






5 1 One-way flow control valve D.ER-GR-1/8-B

6 1 Compressed air reservoir D.ER-VZS-0,4

7 1 3/2-way panel mounted valveD.ER-SV-3-M5




A-103

Please observe the designation in the following pneumatic circuit diagram forconnecting the panel mounted valve.

An actuated 3/2-way panel mounted valve fills the reservoir to system pressurevia a one-way flow-control valve. To set the pressure, compressed air is relea-sed via the flow control from the reservoir until the required pressure is ob-tained.To measure the pressure in the individual pressure circuits, the analogue pres-sure sensor is connected to the respective compressed air distributors; hencethe supply lines to the analogue pressure sensor are denoted by broken lines.

Operational principle

1130

A 12

10V/20mA

1(P)

2(A)

3(R)



A-104

1130

A 12

24V 24V

0V 0V

0V

0V

GND

GND

24V

INPUT

OUTPUT

INPUT

+ 24 V

+ 24 V

+ 24 V

+ 24 V

0 V0 V

0 V 0 V

+

_

Cx

A COMA/mA!

10A

u

!400mAMAX 500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nF

Fu

Au

TTL

DATA HOLD

PEAK HOLD

DC......

AC

A UTO

RANGE

_+

0 10 20 30 40

DC

V

10V/20mA

RD

BK

BU

WH

RD

BK

1

2

34

5

6

BU

SDE-. . .

0V

GND

24V

0

23

1


Comp.Ref. No.











A-105

1130

A 12

0 V

P

+ 2 4 V

P

P1

2

RD( 1)

BK( 3)

BU( 2)

BU( 3)

BK( 4)

RD( 1)

WH(4)

V



A-106

The analogue pressure sensor D.ER-SDE-10-10V/20mA is used to measurethe pressures at points P1 and P2 of the pressure switch D.ER-PEN-M5. To dothis, the sensor is connected via its compressed air port to the respectivepressure circuit. The connection is effected via a self-closing plug-in couplingon the respective compressed air manifold. It is possible for a slight pressuredrop to result in the pressure circuit when the analogue pressure sensor ischanged over. This pressure drop should be ignored.

Part exercise b)Note

• To set the system pressure of 4 bar at P1, the compressed air tubing of theanalogue pressure sensor is connected to the pressure circuit parallel to theservice unit (connection 2 in the pneumatic circuit diagram).

Setting of thesystem pressure

• Set the pressure on the service unit to 4 bar and check or correct thesetting by means of the multimeter reading.

• To carry out this part of the exercise, the analogue pressure sensor is con-nected parallel to the compressed air reservoir in the differential pressurecircuit (connection 1 in the pneumatic circuit diagram).

Setting of thedifferential pressure

The pressure (P2) is calculated from the difference between system and diffe-rential pressure.

The pressure at point (P2) must be 3 bar.

• The compressed air reservoir is charged to system pressure via the panelmounted valve. During this, the adjusting screw of the one-way flow controlvalve is turned to the right-hand stop (flow control closed).

• The adjusting screw is turned slightly to the left. Compressed air is nowescaping from the compressed air reservoir and the pressure in the reser-voir starts to drop. Once the required pressure value has been attained (inthis instance: 3 bar) the flow control is to be closed immediately by meansof the adjusting screw. Observe the pressure on the multimeter at this set-ting. A pressure of 3 bar is thus set at P2.

1130

A 12

Pressure (P2) = System pressure (P1) – Differential pressure


A-107

• If the pressure switch has already been set, the adjusting screw must beturned to the left with a screwdriver until the switch resets.

Part exercise c)

• Setting can now be commenced. To do this, the adjusting screw is turnedslowly to the right until the switch is actuated. Immediately upon switching,cease turning the adjusting screw. Switching will be signalled by means ofthe audible buzzer or the integrated LED.

• The analogue pressure sensor is connected parallel to the service unit. Thisis connection 2 in the pneumatic circuit diagram.

• In order to check the setting, the system pressure at signal input P1 isincreased slowly until the pressure switch switches. Switching will be signal-led by the light emitting diode (LED) of pressure switch D.ER-PEN-M5 aswell as by the sounding of the buzzer.

Checking

• After switching, the manual pressure increase is stopped immediately. Theresponse pressure can be read on the voltmeter with the help of the analo-gue pressure sensor SDE-10-10V/20mA.

If it is not sufficiently accurate, then the entire setting of the pressure switchmust be repeated using the procedure described.

• The actuating pressure applied to the pressure switch is reduced at theservice unit until the pressure switch D.ER-PEN-M5 resets. At the point ofresetting, the reduction of pressure must be stopped immediately. Similar tothe measurement of the switch-on pressure, the reset pressure is deter-mined by means of the analogue pressure sensor D.ER-SDE-10-10V/20mAand the multimeter and entered in table 12/3 of the worksheet.

Part exercise d)

The hysteresis is calculated as follows:

• Repeat the hysteresis measurement for the differential switching pressuresof 2 bar and 3 bar. Enter the measured values in table 12/4 of theworksheet.The hysteresis measurement is carried out as in part exercise d).

Part exercise e)

What information do you obtain regarding the level of contamination of thefilter, if the differential response pressure is increased or if it is reduced?

Question

1130

A 12

Hysteresis = Switch-on pressure (po) - Reset pressure (pu)


A-108

Answer


A 12


1

2

3

4


PDifference (bar) po (bar) pu (bar) Hysteresis (bar)

1.00 4.00

2.00 4.00

3.00 4.00


A-109

Notes


A 12

A-110


Leak testing of compressed air reservoirs Title

Designing a test station for leak testing of compressed air reservoirs. Training aim

Leaks in pneumatic systems lead to an unwanted pressure drop, if the systempressure is greater than the ambient pressure, or to an increase in pressure ifthe system pressure is less than the ambient pressure. It is possible to deter-mine the size of the leak, by observing the time for the pressure change in aclosed system.

Technical knowledge

Compressed air reservoirs are to be leak tested in quality control by means ofa mechanical pressure switch D.ER-PEV-1/4-B.

Problem definition

1130

A 13

B 1.7

Fig. 13/1: Leaking compressed air reservoir


A-111

a) Design a test station pneumatically and electrically in such a way that theleak testing of compressed air reservoirs can be carried out with the me-chanical pressure switch D.ER-PEV-1/4-B. The pressure drop at the leaka-ge point is to be simulated by means of a restrictor.

Exercise

b) Set the testing station according to the following data:- Charging pressure of reservoir 4 bar- Maximum permissible pressure drop 1.5 bar

c) Measure the hysteresis of the pressure switch in respect of the settingcarried out under b).

d) The criteria for a rejected part is a pressure drop within 20 seconds as re-ferred to in part exercise b). Adjust the restrictor in such a way that it justmeets this criteria.

e) Record the pressure drop curve p over time t for the setting carried out un-der d). The recording time is 120 seconds.


1130

A 13


A-112


1130

A 13

1

2

2

3

45

6

7

SDE-...

bar0

1 0

20

3 0

40


Comp.Ref. No.






5 1 One-way flow control valve D.ER-GR-1/8-B

6 1 Compressed air reservoir D.ER-VZS-0.4

7 1 3/2-way panel mounted valveD.ER-SV-3-M5




A-113

Please observe the designation in the following pneumatic circuit diagram forthe connections of the panel mounted valve.

The reservoir is charged to system pressure by means of the actuated 3/2-waypanel mounted valve and the one-way flow control valve. When the push-but-ton is released, the non-return valve closes. The compressed air can escapevia the restrictor and the 3/2-way valve.

Operational principle

If the restrictor is closed, the flow is blocked completely. Compressed air es-capes, if the restrictor is opened; the pressure in the system begins to drop.This simulates the leakage point. The size of the leakage can be adjusted onthe adjusting screw of the restrictor.

1130

A 13

10V/20mA

2(A)

1(P) 3(R)



A-114

In order to adjust the pressure switch D.ER-PEV-1/4-B and to record the t - pcurve, the analogue pressure sensor D.ER-SDE-10-10V/20mA is used with amultimeter as an accurate pressure gauge. The pressure sensor is connectedto the distribution plate D.ER-VERT-SENSOR.

1130

A 13

24V 24V

0V 0V

0V

0V

GND

GND

24V

INPUT

OUTPUT

INPUT

+ 24 V

+ 24 V

+ 24 V

+ 24 V

0 V0 V

0 V 0 V

+

_

Cx

A COMA/mA!

10A

u

!400mAMAX

500 V MAX

!

750V1000V.....

VTTL

OFF

A

mAmV

V

nF

Fu

Au

TTL

DATA HOLD

PEAK HOLD

DC......

AC

AUTO

RANGE

_+

0 10 20 30 40

DC

V

10V/20mA

RD

BK

BU

WH

RD

BK

WH

12

34

5

6

SDE-. . .

0

23

1


Comp.Ref. No.





4 1 Adapter unit D.ER-AE-101AF





B 7.1


A-115

To carry out this part exercise, the normally closed contact of the pressureswitch is used for signal generation.

• In order to adjust the charging pressure, a pneumatic connection must beestablished between the service unit D.ER-FRC-1/8-S and the compressedair reservoir D.ER-VZS-0.4. The panel mounted valve D.ER-SV-3-M5 re-mains activated during the process of adjustment. The system pressure atthe service unit is set at precisely 4 bar. The pressure is set accurately onlyif a signal change of the analogue pressure sensor D.ER-SDE-10-10V/20mA can no longer be detected on the multimeter.

Part exercise b)Setting of thefilling pressure

In this exercise, the pressure switch D.ER-PEV-1/4-B is used in such a way,that an electrical signal is generated if pressure is dropping to the switch-offpoint (pu = 2.5 bar). The signal voltage is connected to the distribution unitD.ER-VERT-SENSOR via the normally closed contact.

Setting of theresponse pressure

• Prior to the setting procedure, the reservoir is charged to system pressure(4 bar) and the restrictor closed.

• In order to make the setting, the pressure in the compressed air reservoir isreduced slowly via the flow control valve until a pressure of 2.5 bar is re-ached. At this point, the flow control valve is closed by the adjustmentscrew and the air flow blocked.

• If pressure falls below 2.5 bar during the adjustment, then the pressure inthe reservoir can be increased again by briefly activating the panel mountedvalve. After this, the pressure adjustment can be repeated.

1130

A 13

0 V

P

+ 2 4 V

PRD( 1)

BK( 3)

WH(4)

BU(2)

RD(1)

BK(4)WH(2)

V



A-116

• The pressure on the pressure switch is set at 2.5 bar. The adjusting screwof the pressure switch is turned to the left until the pressure switch swit-ches, whereby the buzzer on the distribution plate remains silent. After this,the adjusting screw is turned slowly to the right until the pressure switchswitches off and a buzzer sound is generated on the distribution plate viathe normally closed contact.

Setting of thepressure switch

Testing of the setting is carried out as follows:

• Create a system pressure of 4 bar by means of the push-button valve

• Lower the pressure slowly via the flow control valve

• Observe the signal change of the pressure switch when pressure falls be-low 2.5 bar (buzzer sounds).

Part exercise c)

In order to carry out this part exercise, the analogue pressure sensorD.ER-SDE-10-10V/20mA and the pressure sensor D.ER-PEV-1/4-B are pneu-matically connected parallel to the service unit D.ER-FRC-1/8-S.

Note

Monitoring ofsetting

1130

A 13

SD

E-.

..

ba r0

10

20

30

40



A-117

Before starting the measurement, the pressure switch must be in the unactua-ted state, i.e. the pressure must be less than 2.5 bar.

• In order to measure the switch-on point for rising pressure (po), pressure isincreased slowly at the service unit until the pressure switch is actuated.Because the pressure switch is used as a normally closed contact, thebuzzer sound stops when the switching point (po) is reached.

• At this point, the increase in pressure is stopped and the switch-on pressu-re (po) is read on the multimeter.

• Transfer the pressure value to table 13/3 on the worksheet and calculatethe hysteresis.

To carry out this exercise, the pneumatic circuit of part exercise a) must beconstructed again.

Part exercise d)

• The compressed air reservoir is filled via the panel mounted valve to acharging pressure of 4 bar.

• Immediately after the panel mounted valve is released, timing starts. Timingis completed when the pressure switch is actuated. This period must be 20seconds. If there are deviations, the throttle adjustment must be correctedand the measurement carried out again.

It is recommended that the pressurised reservoir should be re-charged to apressure of 4 bar via the panel mounted valve for each measuring point. Meas-urement starts from the moment the panel mounted valve is released.

Part exercise e)

• Wait until the measuring time for each measuring point is completed. Readthe pressure value on the multimeter and enter this measuring value intable 13/4 of the worksheet. The time gap between each individual measu-ring point is 10 seconds.

• Transfer the values from table 13/4 to the diagram (fig.13/7) of theworksheet and draw the curve.

A compressed air reservoir is charged with compressed air for leak testing.What is the required level of air pressure in the compressed air reservoir forthe test to be carried out by means of a mechanical pressure switch?

Question

1130

A 13


A-118

Answer


A 13


1 2.50

2 2.50

3 2.50

4 2.50


0 s

1

2

3

4

6

bar

p

t

20 40 60 100 120 160

Fig. 13/7: Pressure/time diagram

t (s) 10 20 30 40 50 60 70 80 90 100 110 120

p (bar)

Table 13/4: Truth table for pressure drop

A-119

Notes


A 13

A-120


Commissioning of a back pressure switch Title

To learn about the function, connection and the setting of a back pressureswitch for filling level monitoring.

Learning content

Back pressure switches signal the filling level of fluids in containers, wherebythe riser pipe of a back pressure sensor is lowered into the fluid. When thefluid level rises, the air contained in the riser pipe pushes against the pressureinput of the switch.

Technical knowledge

The water supply to the drum of a washing machine is stopped, when thefilling level specified on the washing program has been reached. A back pres-sure switch is used to monitor the filling level. The back pressure switch is tobe set at a given filling level.

Problem definition

1130

A 14

B 7.1

10

23

4

30

60

90

0

5

Fig. 14/1: Filling level in washing machine drum


A-121

a) Assemble the measuring device. Establish the electrical connection be-tween the back pressure switch D.ER-SDS and distribution plate D.ER-VERT-SENSOR.

Exercise

b) Set the pressure switch so that it switches at a water level of 5 cm.Check the setting you have carried out.

Please observe the user notes in the introduction section when carrying outthe exercises. Appropriate information regarding connection method and addi-tional technology can be found in the corresponding data sheets in the appen-dix.

1130

A 14


A-122


1130

A 14

+ 24 V

+ 24 V

+ 24 V

+ 24 V

0 V0 V

0 V 0 V

RD

BK

1

2

3

Fig. 14/2: Assembly and electrical connection

Comp.Ref. No.


1 1 Back pressure switch D.ER-SDS

2 1 Beaker D.AS-RK





A-123

The back pressure switch D.ER-SDS contains a normally open contact, whichis actuated by means of a pressurised diaphragm. The normally open contactswitches the connected voltage signal to the buzzer of the distribution plate.The back pressure switch has a microswitch as a switch contact. A short-cir-cuit will damage the switching contacts if the signal is switched to 0 V and notto the buzzer.

Note

• Fill the beaker with water until the tube is immersed up to 5 cm. If necessa-ry, mark the filling level on the beaker.

Part exercise b)

• If the back pressure switch has switched at this level, the adjusting screwmust be turned to the left until the switch resets and the buzzer stops.

• Now turn the adjusting screw slowly to the right until the back pressureswitch switches. When the switching point is reached, the buzzer will soundon the distribution plate. Stop turning the adjusting screw immediately afterthe switching point has been reached.

• The beaker is emptied prior to checking the setting. Then, the water isslowly poured into the beaker again until the back pressure switch switches.The filling level should now be 5 cm again. If this is not the case, then thesetting procedure must be repeated as described above.

Checking

What other application possibilities are there for a back pressure switch in thedomestic sector?

Question

1130

A 14

0V

+24V

P

RD

BK



A-124

Solutions

Exercises


strain gauges . . . . . . . . . . . . . . . . . . . . . . C-3A 2: Strain gauges connected in series . . . . . . . . . . . . . C-5A 3: Connecting a measuring bridge amplifier . . . . . . . . . . . C-7A 4: Calibrating a force sensor using a quarter-bridge circuit . . . . . C-9A 5: Calibrating a force sensor using a half-bridge circuit . . . . . . C-11A 6: Calibrating an industrial force sensor . . . . . . . . . . . . C-13A 7: Force measurement on pneumatic cylinders using an industrial

force sensor . . . . . . . . . . . . . . . . . . . . . . C-15

Pressure measurementA 8: Commissioning of an analogue pressure sensor . . . . . . . . C-17A 9: Characteristic curve of an analogue pressure sensor . . . . . . C-19A10: Setting of a mechanical pressure switch . . . . . . . . . . . C-23A11: Setting of an electronic pressure switch . . . . . . . . . . . C-25A12: Using an electronic pressure switch

as a differential pressure switch . . . . . . . . . . . . . . C-27A13: Leak testing of compressed air reservoirs . . . . . . . . . . C-29A14: Commissioning of a back pressure switch . . . . . . . . . . C-31

1130

C

Solutions Festo Didactic

C-1

1130

C

Solutions Festo Didactic

C-2

Under tension, the resistance of a strain gauge increases; when compressed,the strain gauge is shortened, and the resistance is reduced. The resistancechanges are very small (a few milliohms).

Part exercise b)

Part exercise c)

Part exercise d)

The shape of the strain gauge changes in the same way as the surface of thedeflecting arm, because the strain gauge is attached to this spring component.If plastic deformation of the deflecting arm occurs with the introduction of alarge force, then the resistance value of the unloaded strain gauge also chan-ges. In this case, the resistance of the strain gauge deviates slightly from itsinitial output resistance.

Answer

1130

A 1

Resistance of an unloaded strain gauge: 350 Ohm

Change in resistance ∆RSG = 0.2 Ohm

The resistance of a loaded strain gauge is:

greater

smaller

remains the same

Table 1/2: Qualitative signal change of a strain gauge with tensile stress

Resistance of an unloaded strain gauge: 350 Ohm

Change in resistance ∆RSG = 0.2 Ohm

The resistance of the loaded strain gauge is:

greater

smaller

remains the same

Table 1/3: Qualitative signal change of a strain gauge with compressive stress

B 2.1

Percentage resistance change ∆R% = 0.057%

Table 1/4: Percentage resistance change

Solution sheet Festo Didactic

C-3

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A 1


C-4

If a deflecting arm is loaded, one side is always under tension and the otherside under compression. This means that one strain gauge is stretched andthe opposite strain gauge compressed. As a result of this, the resistance chan-ges possess different signs.

Ideally, the sum of the resistance changes of the two strain gauges connectedin series should therefore equal zero irrespective of the load on the deflectingbeam. Because of production conditions, however, all individual strain gauges(SG) are different. Therefore, very slight resistance changes may occur whenthe tests are carried out.

Part exercise b)

Part exercise c)

When a deflecting arm is loaded, the strain gauges on the opposite side under-go a similar, but opposing change in resistance. This characteristic is used forsignal evaluation.

Note

If plastic deformation of the deflecting beam occurs due to the application ofexcessive force, then the resistors of the strain gauge in the unloaded statusalso change. Due to the bending load, the resistance change of the two straingauges is opposing and of an equal amount. Therefore, the total resistancedoes not change.

Answer

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A 2

Resistance of the unloaded strain gauge: 700 Ohm


greater

smaller

remains the same

Table 2/2: Qualitative signal change if pressed downwards

Resistance of the unloaded strain gauge: 700 Ohm


greater

smaller

remains the same

Table 2/3: Qualitative signal change if pressed upwards

B 4.3


C-5

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A 2


C-6

On the tension side, the strain gauge is stretched and its resistance increases.Due to this resistance change, the voltage drop increases across the straingauge. The millivolt signal resulting from this is amplified to the volt range inthe signal amplifier.

Part exercise c)

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A 3

The signal change on the amplifier output lies in the:

Millivolt range

Volt range

Table 3/2: Qualitative signal change

Amplification factor a = 500

Amplification output voltage VO = 0.36 Volt

Table 3/3: Amplification output voltage


C-7

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A 3


C-8

Depending on the deflecting arm force sensor and the measuring bridge ampli-fier, the results in this sample solution may vary slightly from the measuredvalues determined by you.

Part exercise a)

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A 4

Mass (g) Force (N) Voltage (V)

0 0.0 0

20 0.2 0.02

50 0.5 0.05

100 1.0 0.11

200 2.0 0.22

500 5.0 0.57

Table 4/3: Table of values for sensor characteristic curve

1 2 3 4 50

1

2

F

V

N

V

Fig. 4/5: Characteristic line of deflecting arm force sensor inquarter-bridge circuit


C-9

To determine a force from the diagram

To do this, a line (x) is drawn parallel to the force axis from point A of thesignal axis. From the intersection point (S) a line (y) is drawn parallel to thesignal axis (V). The resulting intersection point (W) with the force axis gives thevalue of the force to be determined.

Part exercise b)

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A 4

Voltage (V) Force (N) Mass (g)

0.15 1.5 150

Table 4/4: Example for determining the force of a given mass

1 2 3 4 50

1

2

F

V

N

SA y

x

W

V

Fig. 4/6: Procedure for determining force


C-10

Depending on the deflecting arm force sensor used and the measuring bridgeamplifier, the results in this sample solution may vary slightly from the measu-red values determined by you.

Part exercise b)

By using the deflecting arm force sensor with a half-bridge circuit, double thesignal strength of a quarter-bridge circuit is generated with the same load.Thus the deformation of the second strain gauge ensures that the detuning ofthe Wheatstone bridge circuit is twice as strong.

Note

If you have used the same weight for the force measurement as in exercise 4,you will detect a doubling of the signal.

The resistance changes of the two strain gauges oppose each other and are ofthe same magnitude. Due to the half-bridge circuit, the signal is doubled com-pared to the quarter-bridge circuit. Because the characteristic curve of the half-bridge circuit is twice as steep as the characteristic curve of the quarter-bridgecircuit, this results in a doubling of the signal resolution.

Answer

1130

A 5

Mass (g) Force (N) Voltage (V)

20 0.2 0.04

50 0.5 0.11

100 1.0 0.22

200 2.0 0.45

500 5.0 1.14

Table 5/3: Table of values for the characteristic line of the sensor

1 2 3 4 50

1

2

F

V

N

V

Fig. 5/5: Characteristic curve of deflecting arm force sensor in half-bridge circuit


C-11



Part exercise c)

The half-bridge circuit generates double the signal strength for a given force onthe deflecting beam. This is why double the signal strength is recorded whileusing the same weight as in exercise 4.

Answer

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A 5

Voltage (V) Force (N) Mass (g)

0.3 1.5 150

Table 5/4: Example for determining the weight of a particular mass

1 2 3 4 50

1

2

F

V

N

x S

yA

W

V

Fig. 5/6: Procedure for determining the force


C-12

Depending on the force sensor used, the results in this sample solution maydeviate slightly from the measured values determined by you.

Part exercise b)

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A 6

Mass (kg) Force (N) Voltage (V)

0 0 0.00

1 10 0.12

2 20 0.24

3 30 0.36

4 40 0.48

5 50 0.60

6 60 0.72

7 70 0.84

8 80 0.96

9 90 1.08

10 100 1.20

Table 6/3: Table of values for characteristic line of the sensor

0 2 0 4 0 6 0 8 0 10 0 1 2 0 1 4 0 16 0 2 0 0N

F

1.60

V

2.00

1.40

1.20

1.00

0.80

0.60

0.40

0.20

1.80

2.40

V

Fig. 6/5: Characteristic line of force sensor


C-13

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A 6


C-14

The measuring values depend on the actual cylinder and force sensor used.The values in the following table solution may therefore vary from your meas-urements.

Part exercise b, c)

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A 7

Pressure(bar)

F(theor) (N) Voltage (V) Factual (N) FR (N)

1.0 49.1 0.50 41.7 7.4

2.0 98.2 1.06 88.3 9.9

3.0 147.3 1.63 135.8 11.5

4.0 196.3 2.20 183.3 13.0

Table 7/3: Table for determining the cylinder force


C-15



Part exercise d)

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A 7

0 2 0 4 0 6 0 8 0 100 120 140 160 200N

F

1.60

V

2. 00

1.40

1.20

1.00

0. 80

0.60

0. 40

0.20

1. 80

2. 40

A x

y

S

W

V

Fig. 7/6: Procedure for determining force

Voltage (V) Force (N)

0.9 75

Tabelle 7/4: Example of force calculation


C-16

Part exercise a)

A reliable wiring colour identification code enables the user to carry out theassembly of an analogue pressure sensor correctly.

1130

A 8

Connection Plug colour

+ 24 V red

0 V blue

Voltage signal black

Current signal white

Table 8/3: Plug colours


C-17

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A 8


C-18

Depending on the accuracy of the measuring device and the analogue pressu-re sensor used, the results below may vary slightly from the measured valuesdetermined by you.

Part exercise b)

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A 9

p (bar) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Voltage (V) 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

Table 9/3: Table of values for determining the voltage characteristic line

1 2 3 4 6

4

0

1

2

3

V

p

ba r

V

Fig. 9/7: The voltage characteristic line


C-19

Part exercise c)

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A 9

1 2 3 4 60

p

bar

mA

16

12

8

4

Fig. 9/8: The current characteristic line

p (bar) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Current(mA)

4.0 4.8 5.6 6.4 7.2 8.0 8.8 9.6 10.4 11.2 12.0

Table 9/4: Table of values for determining the current characteristic line


C-20

To determine a pressure value from the characteristic line

To do this, a line (x) is drawn parallel to the force axis from point A of thesignal axis. From the intersection point (S) a line (y) is drawn parallel to thesignal axis (V) resulting intersection point (W) with the force axis gives thevalue of the force to be determined.

Part exercise d)

With different evaluation units (PLC, display, etc.), it is often advantagous touse sensors with different characteristic curves. If the evaluation unit canrecord the entire signal range of the sensor, then the resolution increases.

Note

Measuring device Voltage (V) Current (mA) p (bar)

Pressure gauge ————— ————— 3.60

SDE-10-10V/20mA 3.75 ————— 3.75

SDE-10-5V/20mA 2.50 ————— 3.75

SDE-10-5V/20mA ————— 10.0 3.75

Table 9/5: Example of pressure measurement

0

V

1 2 3 4 5 6 7 8 bar 10

p

1

2

3

4

5

6

7

8

10

p

x S

y

AV

Fig. 9/9: Procedure for determining pressure

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A 9


C-21

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A 9


C-22

Part exercise b)

The measured values depend on the setting of the hysteresis adjustmentscrew. The values below may therefore differ from your measurements.

Part exercise d)

Part exercise e)

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A 10


3.00 2.07 0.93

Table 10/4: Table of values for determining hysteresis


1.00 0.48 0.52

2.00 1.29 0.71

3.00 2.07 0.93

4.00 2.96 1.04



1The results of your measurementsdepend on the setting of theadjustment screw.

2

3

4

Table 10/3: Table of values for determining response pressure


C-23

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A 10


C-24

Part exercise b)

The hysteresis of individual pressure switches depends on their mechanicalconstruction. The values of the results below may therefore differ from yourmeasurements.

Part exercise d)

Part exercise e)

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A 11


3.00 2.87 0.13



1.00 0.96 0.04

2.00 1.93 0.07

3.00 2.87 0.13

4.00 3.83 0.17



1The results of your measurementsdepend on the setting of theadjustment screw.

2

3

4

Table 11/3: Table of values for determining response pressure


C-25

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A 11


C-26

The hysteresis of individual pressure switches depends on their mechanicalconstruction. The values of the results below may therefore differ from yourmeasurements.

Part exercise d)

Part exercise e)

If the differential pressure is increased, there is a higher degree of contaminati-on; if reduced, then the contamination is less.

Answer

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A 12

pDifference (bar) po (bar) pu (bar) Hysteresis (bar)

1.00 4.00 3.96 0.04


pDifference (bar) po (bar) pu (bar) Hysteresis (bar)

1.00 4.00 3.96 0.04

2.00 4.00 3.93 0.07

3.00 4.00 3.87 0.13



C-27

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A 12


C-28

Part exercise c)

Part exercise e)

When filling the compressed air receiver, care should be taken that the fillingpressure is greater than the reset point plus the hysteresis of the pressureswitch. Only an actuated pressure switch can produce a signal at the resetpoint.

Answer

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A 13

t (s) 0 10 20 30 40 50 60

p (bar) 4.0 3.2 2.5 2.1 1.7 1.4 1.2

t (s) 70 80 90 100 110 120

p (bar) 0.9 0.7 0.6 0.5 0.4 0.3

Table 13/4: Table of values for pressure drop

0 s

1

2

3

4

6

bar

p

t

20 40 60 80 100 120 160

Fig. 13/7: Diagram showing time-related pressure drop


3.45 2.50 0.95



C-29

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C-30

A further possibility of application for back pressure switches in the field ofdomestic appliances is monitoring the filling level in dish washers.

Answer

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A 14


C-31

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C-32

Sensors for Handling Processing Technology Sensors for Force Pressure

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Transcript of Sensors for Handling Processing Technology Sensors for Force Pressure