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  NATIONAL UNIVERSITY OF SINGAPORE EXAMINATION FOR (Semester I: 2009/2010) EE3302/EE3302E – INDUSTRIAL CONTROL SYSTEMS   November/December 2009 - Time Allowed: 2  Hours 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.  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 passenger’s head. Q1 is continued on Page 3 Standing zone with load cell, LCMotorisedextensible pole, MPInfrared thermometer, TMPhotoelectricsensor to locateforehead, PSPassenger Standing zone with load cell, LCMotorisedextensible pole, MPInfrared thermometer, TMPhotoelectricsensor to locateforehead, PSPassenger  FWD HME (a) Motorised PoleMPTM ENTEMP (b) Thermometer  FWD HME (a) Motorised PoleMPTM ENTEMP (b) Thermometer   EE3302/EE3302E Industrial Control Systems/ Page 3 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). This measurement will be compared against a high threshold of 37.6 o C and low threshold of 36.5 o C. 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 logic controller (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 valueSPSetpointProcess value Analog_In PVIO_ADDR I/O addressQComparison 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<SP. PV and SP are real while Q is Boolean. Fig 3   EE3302/EE3302E Industrial Control Systems/ Page 4  Q.2 Fig 4 shows the block diagram of a process with input u , output  y  and subject to measurable disturbances w 1   and w 2 . G  p  is the process transfer function and G w1   and G w2  are the transfer functions relating to the effects of w 1   and w 2 on  y  respectively. Fig 4 Three step tests were done with unit steps applied to u, w 1   and w 2   respectively and shown in Fig 5. (a)   Provide transfer function models for G  p  , G w1   and G w2  based on the step responses in Fig 5. (6 marks) (b)   Provide the block diagram of a feedback only control system using a proportional controller with proportional gain K  c  limited to K  c <10 . Explain if this controller is adequate for restricting the effects of the disturbances w 1   and w 2   . (5 marks) (c)   Modify the proportional feedback control system in (b) to additionally incorporate a suitable advanced control scheme that you know to yield better  performance. Explain how each block is to be designed. (10 marks) (d)   Verify mathematically that your design in (c) has stable closed-loop poles. (4 marks) Q2 is continued on Page 5 + u yw 1 w 2 G p G w1 G w2 v 2 v 1 z   + u yw 1 w 2 G p G w1 G w2 v 2 v 1 z
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