Sensors and TransducersSensors and TransducersSensor is an element that is

capable of producing a signal corresponding to the quantity measured.

Transducers are element that when subjected to physical change experience a related change.

Performance terminology Performance terminology used in sensorsused in sensorsRange and spanErrorAccuracySensitivityHysteresis errorRepeatability StabilityDead bandOutput impedance

Displacement, position and Displacement, position and proximity sensorsproximity sensorsDisplacement sensors are

concerned with the amount by which the object is moved

Position sensor is concerned with the determination of the position of the object

Proximity sensors is a form of position sensor that detects weather the object has moved

Potentiometer sensorPotentiometer sensorThis type of sensors use a

resistance element with a sliding contact which can be moved over the length of the element

Strain gauged elements Strain gauged elements This electrical strain gauge is a

metal wire, metal foil strip or a strip of semiconductor that can be stuck on to anysurface

Capacitive elementsCapacitive elementsHere the principle of a capacitor

is used for the measurement purpose

Linear variable differential Linear variable differential TransformersTransformers

Optical Encoder

Pneumatic sensors◦They use compressed air for

detecting the displacement or proximity of an object

◦Change in air pressure is used for detection

Proximity switchesProximity switches

Strain Gauge load cell ◦It uses electric resistance for

monitoring strain

Temperature Sensors◦Bimetallic strips

Thermistors◦It is made from mixtures of metal

oxides which are semiconductors◦The resistnce of a conventional

metal oxide thermistor decreases in a very non-linear with an increase in temperature as compared to normal metal

Thermocouples

Signal conditioningSignal conditioningThe output from a sensor is raw

and has to be processed.The signal can be too small,

hence have to be amplified or can be non linear, analogue all this signals have to be converted into desired form

All these changes can be referred to as signal conditioning

Signal conditioning Signal conditioning processesprocessesProtectionRight type of signalGetting to right level

◦For example converting to dc Eliminating noiseManipulation

◦for example converting non-linear

Operational amplifiersOperational amplifiersAn amplifier is used to attain voltage gain

in a system, voltage gain being the ratio between output and input voltage

An operational amplifier is a high gain d.c amplifier, the gain being in the order of 100000 or more.

The operational amplifier has two inputs namely inverting and non-inverting input

Op-Amp IC 741Op-Amp IC 741

Inverting amplifierInverting amplifier

Non-inverting amplifierNon-inverting amplifier

Summing amplifier Summing amplifier

Integrating AmplifierIntegrating Amplifier

Difference amplifierDifference amplifier

FilteringFiltering

MultiplexersMultiplexersIt is a circuit into which a input

can be given from a number of sources

Input channels can be individually selected and send to an ADC

It is essentially a electronic switching device

Data acquisition DAQData acquisition DAQIt is the process of taking data from

sensors and inputting that data into a computer for processing

The sensors are connected to DAQ via some kind of signal conditioners

DAQ board is a combination of multiplexer, amplifiers, ADC, control circuits

Pneumatic and Hydraulic Pneumatic and Hydraulic Systems Systems Pneumatic signals are often used

to control final control elements The main drawback is the

compressibility of airHydraulic system are used where

higher power control is required Pressurised oil is used for the

system

Pneumatic and Hydraulic Pneumatic and Hydraulic Systems Systems

Control ValvesControl ValvesControl valves are used in

hydraulic and pneumatic systems to direct and regulate the flow

They are intended to vary the rate of flow of a fluid