Hnc control system and automation 1st assignment

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Home>Science homework help>Hnc control system and automation 1st assignment

1. Choose a simple single control loop used on a process you are familiar

with (it could be domestic or industrial).

(a) Explain why the control is necessary.

(b) Write a description of the control system.

(c) Produce an algorithm of the control system.

(d) Draw a block diagram of the control system.

(e) State the type(s) of signal used in the process.

(f) State whether the control is open or closed loop, feed forward or

feedback.

(g) State and describe the sensor used for measuring the process variable

to be controlled.

2

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© Teesside University 2011

2. The curve in FIGURE 1 shows the response of a bare thermocouple

which has been subjected to a step change in temperature from 50°C to

10°C. Assuming that the bare thermocouple behaves as a single

transfer lag system, determine the mathematical relationship between the

temperature (T) and time (t) [i.e. determine the equation relating T to t].

FIG. 1

Time, ts

Te m

pe ra

tu re

, T

°C

2 4 6

50

40

30

20

10

0

0 18 2014 168 10 12

3

Teesside University Open Learning (Engineering)

© Teesside University 2011

3. FIGURE 2 shows the behaviour of a control system which has been

switched from manual to automatic mode. Comment on the conditions

existing in the control loop which would have given rise to the response

shown.

FIG. 2

4. FIGURE 3 shows an open loop system containing a distance velocity lag

and a single transfer lag.

FIG. 3

If the system input xi is subjected to a step disturbance from 2 units to

12 units, plot the response of xo on a base of time. Determine graphically,

and verify mathematically, the time taken for the output to change by

4 units.

Distance - velocity lag of

4.0s

xoxi Single tansfer lag of τ = 5s

System output

Time

4

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5.

FIG. 4

Derive the closed loop transfer functions for the system shown

in FIGURE 4 and show that for large values of G the value of

approaches unity.

6. FIGURE 5 shows an electrically heated oven and its associated control

circuitry. The current, I, to the oven's heating element is fed from a

voltage-controlled power amplifier such that I = εK1. A voltage, VD, derived from a potentiometer, sets the desired oven temperature, TD. The

oven temperature is measured using a thermocouple that, for simplicity, is

assumed to generate a constant emf of 10 µV per degree Celsius. The effect of the ambient temperature is ignored.

FIG. 5

Power supply12 V

VD Power amplifier

Voltage amplifier

TO = kOI

Thermocouple

Vt = ktTOVM = k2Vt

I = εk1 Heater

ε = VD - VM

Oven

V

V o

i

+ –

G

K1 K2Vi Vo

5

Teesside University Open Learning (Engineering)

© Teesside University 2011

(i) Represent the arrangement by a conventional control-system block

diagram. Identify the following elements in the block diagram:

input; error detector (comparator); controller; controlled

element; detecting element and feedback loop.

(ii) Derive an expression for the transfer function of the system, in terms

of the system parameters k1, k2, kO and kt.

(iii) Using the data given in TABLE A, calculate the oven temperature

when the potentiometer is at its mid-point.

TABLE A

PARAMETER VALUE

kt 10 µV/°C

kO 6.9 °C/A

k1 6 A/V

k2 2400

6

Teesside University Open Learning (Engineering)

© Teesside University 2011

7. (a) Derive an expression for the closed loop transfer function for the

control system shown in FIGURE 6.

FIG. 6

(b) Show that the value of is 0.8 when the following values of the

various control loop elements are adopted:

K1 = 10

K2 = 2

K3 = 5

K4 = 0.4

K5 = 0.9.

θ θ

o

i

K1 K3

θi θo +

– K4K2+

–

yx

K5

θ θ

o

i

7

Teesside University Open Learning (Engineering)

© Teesside University 2011

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