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NATIONAL UNIVERSITY OF SINGAPORE

EXAMINATION FOR

(Semester I: 2009/2010)

EE3302/EE3302E INDUSTRIAL CONTROL SYSTEMS

November/December 2009 - Time Allowed: 2Hours

INSTRUCTIONS TO CANDIDATES:

1. This paper contains FOUR (4)questions and comprises SEVEN (7)pages.

2. Answer all questions.

3. All questions carry equal marks.

4. This is an open book examination.

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EE3302/EE3302E Industrial Control Systems/ Page 2

Q.1 You are required to design the controller for an automated low cost temperature

measurement station to be integrated to airport security checkpoints using long range

infrar-red sensor as shown in Fig 1.

Fig 1

The passenger will stand within the standing zone which is a platform fitted with a

load cell (LC) below it. The load cell will turn on and give a high signal only when a

passenger stands on it. At this time, the motorized extensible pole (MP) will extend

downwards till the infrared thermometer (TM) is pointed at the forehead of the

passenger. The motorized extensible pole (MP) is controlled by two inputs, FWD and

HOME as shown in Fig 2(a). A high signal at the FWD input will extend it

downwards. A high signal to the HME input will retract it back to a preset home

position. It will retain its present position if no input signals are received.

Fig 2

This positioning of the pole relative to the forehead of the passenger is achieved

through the photoelectric sensor (PS) which will turn on, giving a high signal when

the optical path is first blocked by the passengers head.

Q1 is continued on Page 3

Standing zone with load cell, LC

Motorised extensible pole, MP

Infrared thermometer, TM

Photoelectric

sensor to locate

forehead, PS

Passenger

Standing zone with load cell, LC

Motorised extensible pole, MP

Infrared thermometer, TM

Photoelectric

sensor to locate

forehead, PS

Passenger

FWD HME

(a) Motorised Pole

MP

TM

EN

TEMP

(b) Thermometer

FWD HME

(a) Motorised Pole

MP

TM

EN

TEMP

(b) Thermometer

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At this time, the thermometer (TM) will be activated to take a measurement. When it

is activated by sending a high signal to its input (EN), an analog temperature

measurement will be available at its output (TEMP) as shown in Fig 2(b). Thismeasurement will be compared against a high threshold of 37.6oC and low threshold

of 36.5oC. If the temperature is higher than the high threshold, a red LED (RD) will

be lighted. If the temperature is lower than the low threshold, an amber LED (AM)

will be lighted to indicate a possible fault. Otherwise, a green LED (GN) will be

lighted. Based on the lighted LED, the airport staff will then direct the passenger to

either proceed with his journey when the green LED lighted or to a holding area for

further attention when the red or amber LED is lighted. Thereafter, he will press a

reset button (RST) to get ready for the next passenger. The activation of the reset

button will retract the motorized extensible pole to a preset home position and turn off

all the LEDs and the system is ready to receive the next passenger.

(a) Provide a diagram to show the physical connections of the programmable logiccontroller (PLC).

(5 marks)

(b) Provide a Sequential Function Chart for the sequence control.(8 marks)

(c) Provide a ladder program to implement the logic.(12 marks)

The following function blocks in Fig 3 are available for use.

Comparator

PVProcess value

SPSetpointProcess

value

Analog_In

PV

IO_ADDRI/O address Q Comparison result (Bool)

Analog_In:This is the function block to allow access to analog inputs by setting the

IO_ADDR input to the address of the analog sensor.

Comparator:This is a function block which sets its output Q if its input PV

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Q.2 Fig 4 shows the block diagram of a process with input u, output y and subject to

measurable disturbances w1and w2. Gp is the process transfer function and Gw1andGw2are the transfer functions relating to the effects of w1and w2 onyrespectively.

Fig 4

Three step tests were done with unit steps applied to u, w1and w2 respectively and

shown in Fig 5.

(a) Provide transfer function models for Gp, Gw1and Gw2based on the step responsesin Fig 5.

(6 marks)

(b) Provide the block diagram of a feedback only control system using a proportionalcontroller with proportional gain Kclimited to Kc

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Fig 5

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Q.3 Consider the closed-loop system in Fig 6 where

ssGp

1)( =

and the saturation nonlinearity is given as

=

1)(1

1)(1)(

1)(1

)(

te

tete

te

tu

(a)Findy(t) ifs

sR1

)( = .

(5 marks)

(b) Assumes

sR2

)( = .

(i) Find )(ty for 10 t .

(5 marks)

(ii) Find )(ty for 1t .

(10 marks)

(iii) Sketch )(tu . No workings are necessary.

(5 marks)

Fig 6

Q.4 Consider the feedback control system in Fig 7 where

( ).)(

,1

1)(

2

uc

p

KsG

Ts

ssG

=

+

=

The Ziegler-Nichols ultimate cycling experiment was performed with 0=r and thesustained oscillations are shown in Fig 8.

(a)Estimate the ultimate gain, uK , and the ultimate period, uT , from Fig 8.

(8 marks)

(b) Determine Tand .

(10 marks)

(c) Sketch Fig 8 in your answer booklet and superimpose on the control signal,

u , the relay oscillation that would produce approximately the output, y , in Fig 8.

(7 marks)

Q4 is continued on Page 7

Gp(s)R(s)

E(s) U(s)Y(s)

_

+Saturation

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Fig 7

0 1 2 3 4 5 6 7 8 9 103

2

1

0

1

2

3

y

Time(seconds)

0 1 2 3 4 5 6 7 8 9 1010

5

0

5

10

u

Time(seconds)

Fig 8

END OF PAPER

Gp(s)Gc(s)u

r y+

_

0910sem1-ee3302

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