Lecture 1: Automation in Environmental Engineering Lecture 1

8/10/2019 Lecture 1: Automation in Environmental Engineering Lecture 1

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Automation in EnvironmentalEngineering

dr in ! . Patryk Wjtowicz


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Automation - definition

Automation is the use of control systems,equipment and informationtechnologies to reduce the need for humanparticipation in controlling processes


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Automation - definition

Automation - 1. The implementation ofprocesses by automatic means. 2. Thetheory, art, or technique of making aprocess more automatic. 3. Theinvestigation, design, development, andapplication of methods for renderingprocesses automatic, self-moving, or self-

controlling. 4. The conversion of aprocedure, a process, or equipment toautomatic operation


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Some more definitions

Automatic control - The type of control inwhich there is no direct human action onthe controlling device

Automate - To convert a procedure, aprocess, or equipment into an automaticoperation


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and more definitions...

Automatic - 1. Self-acting or operating byits own mechanism when actuated bysome impersonal influence, as, forexample, a change in current strength,pressure, temperature, or mechanicalconfiguration 2. A machine that operatesautomatically. 3. Functioning without

intervention by a human operator underspecified conditions, as of a process ordevice


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and more definitions... contd

Regulation - The control of flow or of some other processvariable

Control - 1. One or more of the components in any mechanismthat is responsible for interpreting and carrying out manuallyinitiated directions. 2. In some applications, a mathematicalcheck. 3. Instructions that determine conditional jumps oftenare referred to as "control instructions," and the timesequence of the execution of these instructions is called the"flow of control." 4. Any manual or automatic device forregulating a machine to keep it at normal operation. Ifautomatic, the device is motivated by variations intemperature, pressure, water level, time, light, or otherinfluences. 5. Maintaining a desired set point of steamtemperature during operation

(The Automation, Systems, and Instrumentation Dictionary. 4 th ed. ISA 2005


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Control systems

Control system - a device or set of devicesto manage, command, direct or regulatethe behavior of other devices or systems

There are two common classes of controlsystems, with many variations andcombinations: logic (sequential controls) ,

and feedback (linear controls) and fuzzylogic


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Logic control

Logic controllers may respond toswitches, light sensors, pressure switchesetc. and can cause the equipment to startand stop various operations.

In logic control systems weuse programmable logic controllers (PLC)

or microcontrollers


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Onoff feedback control

Onoff controller (a bangbang controller ),also known as a hysteresis controller, is afeedback controller that switches onlybetween two states (e.g. on and off)

Typical examples are thermostat and aircompressor

In thermostat we have negative-feedback control: when the temperature goes

below a set point, the heater is switched on In air compressor when the pressure dropsbelow the certain threshold, the pump ispowered on


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Positive and negative feedback

Negative feedback - Returning part of anoutput signal and using it to reduce thevalue of an input signal

Positive feedback - a closed loop in whichany change is reinforced until a limit iseventually reached. (e.g. signal

amplification)


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Linear control

Linear control systemsuse linear negative feedback to produce acontrol signal mathematically based on other

variables, in order to maintain the controlledprocess within an acceptable or desiredoperating range

The output from a linear control system into

the controlled process may be in the form ofa directly variable signal, such as a valveopen may vary between 0 and 100% or turn iton or off (pulse-width modulation)


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Fuzzy logic

Fuzzy logic combines easy design of logiccontrollers while still controllingcontinuously-varying systems

Fuzzy logic is a reasoning approach andcomputing method that is used to modellinguistic expressions (such as "somewhatmore than") that have nonbinary truth values

Basically, a measurement in a fuzzy logic

system can be partly true, that is if yes is 1and no is 0, a fuzzy measurement can bebetween 0 and 1.


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Piping and instrumentation diagrams

Piping and instrumentation (PI) diagramsare of fundamental importance in processautomation

P&I diagrams depict, from a process pointof view, measurements and controlschemes in relation to items of plant and

their interconnecting pipework. They arerepresented by means of symbols and tagnumbers .


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Symbols

Symbols are used to represent individualelements such as sensors and valves, orcombinations of elements such asmeasurement channels or control loops.

Symbols are linked together by signal lines .

Tag numbers are written inside circles ,referred to as bubbles or balloons .


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Letter codes and reference numbers

Letter codes indicate the function of theelements and are generic.

Reference numbers are specific toparticular elements and are used foridentification purposes.


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Simple P&I diagram of flow control loop

Note that the elements of the loop are shown in their correct positions in afunctional sense, i.e. the control valve is downstream of the pump and theflow measurement is between the valve and the pump. However, the

symbols do not necessarily indicate their relative positions in a physicalsense, e.g. the flow measurement and valve could be a long way from thepump.

Arrows are normally put on the signals to indicate the direction of flow ofinformation. They may be omitted in obvious and simple diagrams


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Graphical representation of signal types


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Detailed P&I diagram of flow control loop

sight-glass

orifice controlvalve


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Detailed P&I diagram of flow control loop

The pressure drop across the orifice plate is measured using a! p cell FT 47 which transmits the flowrate as an electricalsignal to the totaliser FQR 47, the low level switch FSL 47 andthe controller FIC 47.

If the flow drops below some pre-set lower limit the flowswitch FSL 47 will activate a low level alarm FAL 47. FV 47 is a pneumatically actuated diaphragm type of

regulatory valve. It has a positioner attached, as indicated bythe box on the stem of the valve symbol


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Bubbles

Information about the location of an element isindicated by the presence or otherwise of a linethrough its bubble.

No line means that the element is field mounted,i.e. it is installed on or adjacent to a pipe, vesselor some other item of plant.


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Bubbles

A single line through the bubble, as with FAL47 and FIC 47, means that the element islocated in a central control room.

A double line, as with FQR 47, means that it

is panel mounted elsewhere, say on a fieldtermination cabinet.


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Tags

There are several national standards whichrelate to the representation ofinstrumentation and control schemes. Themost important English language ones are BS1646 and ISA S5.1 (ISA - The Instrumentation,Systems, and Automation Society)

Recommended and commonly used inpractice is notation according to ISA standard

Note that the basic symbols and letter codestructure are essentially the same for allstandards


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Letter codes

Letter codes are configured according tofunction.

The first letter corresponds to the measured

variable and, if necessary, may be qualifiedby a modifier. Succeeding letters describe an elements

readout or control functions; these maythemselves have modifiers.

The first letter of all elements within a loopis that of the measured variable (i.e. F forFlow).


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ISA letter codes for tag numbers


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If a loop contains two or more elements with the samefunction they may be distinguished by means ofsuffixes (e.g. A , B ...)

Sometimes the letter code is insufficient to give an

adequate description of the function of an element.Additional information may be provided, either in abox attached to its bubble or as adjacent text.

For example, FT 47 has a square root function tocompensate for the square relationship inherent in theflow measurement by the orifice plate. The total flowcomputed by FQR 47 is obtained by means of anintegral function


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Additional functions for use with tag

numbers


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Function designation


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Function designation


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Serial vs parallel numbering

In serial numbering each channel, loop orscheme has assigned a unique number

In parallel numbering convention, blocksof numbers are allocated according toinstrument type or function, depending onits letter code. This results in similar

elements in different loops havingcontiguous numbers


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Distributed Control Systems (DCS)

A solid line across the symbol means that the function has ashared, screen based display: the absence of a line means thatthe function is inaccessible to the operator.

Visible (on screendisplay)


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Distributed Control Systems (DCS)

A solid line across the symbol means thatthe function has a shared, screen baseddisplay: the absence of a line means thatthe function is inaccessible to theoperator.


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Block diagrams

Block diagram depicts the structure of asystem and shows the functionalrelationship between its various elements


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Symbols and notation used in block

diagrams Block relate to the elements and

represent functions (combinations ofconversion or scaling, factors anddynamics)

Lines between the blocks represent signals Arrows indicates direction of flow of

information Addition or subtraction of signals is

represented by circles with signs (no sign =+)


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Block diagrams

Typical feedback control system (levelcontrol system)


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The general layout of the block diagram

By convention the controlled variablecomes out on the right hand side andexternal inputs are normally shownentering from the left

Signals are represented by single arrows(e.g. they can be physically two or more

wires of electrical wiring) The size of the blocks in diagrams doesntrelate to the physical size of the elements


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Block diagram of level control system


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Block diagram of level control system

The controlled variable ( level h ) is measured and fedback to the controller where it is compared with thereference signal h r (set point ), to produce the errorsignal e (deviation from set point)

The controller produces an output u (as a function of

error) which manipulate valve opening and the outletflow f 0 The resultant level in the tank (h) depends upon the

combined effect of its outlet flow and anydisturbances in its inlet flow f 1.


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Comprehensive block diagram of level

control system


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Sub-systems

The control , manipulation and plant sub-systems are often referred to as thefeedforward path , and the measurement sub-system is referred to as the feedbackpath


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Process and load - definition

Process is defined to be the way in which themanipulated variable (MV) affects the controlledvariable (CV)

Load is defined as the relationship between adisturbance (DV) and the controlled variable(CV).

There may be various sources of disturbance theremay be several different loads

According to the principle of superposition, the

net change in controlled variable is the sum of theindividual effects of the process on themanipulated variable and the loads on thedisturbance variables.


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Modes of operation

Most controllers have an auto and manual modes

In automatic the controller output variesaccording to how the PID handles the error

In manual mode the output is not relatedto the error and can be adjusted by hand

to any desired value


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PID

PID controller - ProportionalIntegralDerivative controller is a generic controlloop feedback mechanism (controller)

PID controller calculates an " error " (E -deviation) value as the difference betweena measured process variable and adesired setpoint (SP)

The controller attempts to minimize theerror by adjusting the process controlinputs


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Open vs closed control loops

The operation of a control loop may bedescribed as being either closed or open

Closed loop - all the elements of a loopare functioning interconnected and thecontroller is in auto such that automaticcontrol occurs

When a controller is switched into manual the loop is opened

Lecture 1: Automation in Environmental Engineering Lecture 1

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