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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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22.5 Design of a discrete-time controller 693

Solutions

1 SeeFigure S.23.

2 a[n] =

v[n] − v[n −1]

.SeeFigure S.24.

T

x[n]

T

S 3 a[n]

y[n]

S 3

a[n]

FigureS.23

T

T

1–

3

FigureS.24

T

3

–1

1 –

T

22.5 DESIGNOFADISCRETE-TIMECONTROLLER

Figure22.12showsablockdiagramofasingleloopindustrialcontrolsystem.Thecontrol

system employs feedback to compare the desired value of a process variable with

the actual value. Any difference between the two generates an error signal e(t). This

signalisprocessedbythecontrollertoproduceacontrollersignalm(t).Anamplifieris

oftenpresenttomagnifythissignaltomakeitsuitablefordrivingtheplantthatisbeing

controlled.

Thecontrollercanbeimplementedbymeansofananalogueelectroniccircuit.However,

digital computers are being used increasingly as controllers. The signalse(t) and

m(t) are both continuous in time and so it is necessary to samplee(t) before it can be

used by the computer and to reconstruct the signal generated by the computer to producethecontrolleroutput,m(t).Thearrangementforimplementingadigitalcontroller

isshown inFigure 22.13.

r(t) +

e(t)

Controller

m(t)

Amplifier

Plant

c(t)

Sensor

Figure22.12

Asingle loop industrial controlsystem.

e(t)

Analogue-todigital

converter

Digital

computer

Digital-toanalogue

converter

m(t)

Figure22.13

Block diagramofadigital controller.

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