Engineering - Mechanical Engineering Automation assignment

CSA-1-TMAv2.2.pdf

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MODULE TITLE : CONTROL SYSTEMS AND AUTOMATION

TOPIC TITLE : BASIC PRINCIPLES AND CONTROL

ACTIONS

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CSA - 1 - TMA (v2.1)

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Published by Teesside University Open Learning (Engineering)

School of Computing, Engineering and Digital Technologies

Teesside University

Tees Valley, UK

TS1 3BA

+44 (0)1642 342740

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Before you start please read the following instructions carefully.

1. This assignment forms part of the formal assessment for this

module.

2. You should therefore not submit the assignment until you are

reasonably sure that you have completed it successfully. Seek your tutor's

advice if unsure.

3. Ensure that you indicate the number of the question you are answering.

4. Make a copy of your answers before submitting the assignment.

5. Complete all details on the front page of this TMA and return it with the

completed assignment including supporting calculations where

appropriate. The preferred submission is via your TUOL(E) Blackboard

account:

https://eat.tees.ac.uk

6. Your tutor’s comments on the assignment will be posted on Blackboard.

IMPORTANT

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.

(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. 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

0 2 4 6 8 10 12

Time, ts

14 16 18 20

T em

p er

a tu

re , T C

3. 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.

xi xo Single

transfer lag of  = 5s 4.0s

Distance - velocity lag of

4. 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 = K1. 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 V per degree Celsius. The effect

of the ambient temperature is ignored.

12 V

 = VD - VM

Power supply

I = k1

Heater

Oven

Thermocouple

VM = k2Vt

FIG. 5

Vt = ktTO

Power amplifier

Voltage amplifier

TO = kOI

(a) 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.

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

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

when the potentiometer is at its mid-point.

PARAMETER VALUE

kt 10 V/°C

kO 6.9 °C/A

k1 6 A/V

k2 2400

TABLE A

5. The proportional control system of FIGURE 3(a) has an input, 1, of

10 units. The uncontrolled input, 2, has a value of 50 units, prior to a

step change down to 40 units. The result of this disturbance upon the

output, o, is shown in FIGURE 3(b).

(a) Calculate the change in offset in the output produced by the step

change.

(b) Draw a modified block diagram to show how the offset could be

minimised by the inclusion of another control action. Also, show by

means of a sketch how the modification might be expected to affect

the output response.

the disturbance could be minimised by the inclusion of a third type of

control action.





Fig 3 (a)

o

0 10 20 30 40 50 60

Time (minutes)

Fig 3 (b)

6. (a) FIGURE 5 shows the input and output waveforms for a

proportional plus integral controller. State:

(i) the controller's proportional gain

(ii) the controller's integral action time

Fig 5

(b) FIGURE 6 shows a proportional plus derivative controller that has a

proportional band of 20% and a derivative action time of 0.1 minutes.

Construct the shape of the output waveform for the triangular input

waveform shown, if the input rises and falls at the rate of 4 units per

minute.

Fig 6

Question

No.