Lecture 1: Automation in Environmental Engineering Lecture 1

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Transcript of 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 correspo