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Cork Institute of Technology
Bachelor of Engineering in Mechanical Engineering – Award
Bachelor of Engineering in Manufacturing Engineering – Award
(National Diploma in Engineering in Mechanical/Manufacturing Engineering – Award) (NFQ – Level 7)
Autumn 2005
INDUSTRIAL ELECTRONICS AND CONTROL
(Time: 3 Hours)
INSTRUCTIONS: Answer Five Questions, at least Two from each section. All formula and calculations must be shown.
Examiners: Dr. D. O Mahony Mr. S.P. O’Sullivan Mr. R. Daly Mr. M. Murray Mr. N. Mulcahy Mr. J. Connolly Mr. R. Simpson
Section A ( Industrial Electronics )
Please Use Answer Book A
Q1 A factory has the following single-phase loads distributed across a three-phase four-wire 400V, 50Hz, supply: (i) Between L1 and Neutral 10 kW at 0.82 p.f. lagging (ii) Between L2 and Neutral 12 kW at 0.8 p.f. lagging (ii) Between L3 and Neutral 15 kW at 0.86 p.f. lagging
(a) Draw a fully labelled circuit diagram to represent the loads described above, and calculate the current and phase angle for each phase of the load (12 Marks)
(b) Calculate, or determine by means of a vector diagram, the current in the supply neutral conductor. (8 Marks)
Q2 (a) A 3-phase, 75kW, 400V, 50Hz, 6-pole, delta connected squirrel cage induction motor has a full-load; efficiency of 94%, power factor of 0.84, and running speed of 988 r.p.m. Calculate for full-load conditions, the motor’s: (i) Input power; (ii) Supply current; (iii) Phase (winding) current; (iv) Full-load torque. 12marks (b) Explain the terms; synchronous-speed, slip-speed, and slip of a 3-phase motor. Calculate for the motor in (a): (i) synchronous speed; (ii) % slip; 4 Marks (c) Electronic controllers are the modern method of speed control for 3-phase induction motors. Explain using an appropriate formula, the principle on which the control of the motor speed is implemented. 4 marks
Q3 (a) The Mitsubishi FXo30MR-ES PLC contains 512 Memories of two general types, General and Retentive Memories. Detail the difference between these two memories. (4 marks)
(b) Give an example address of both types of memories detailed above. (2 marks)
(c) Two contactors (KM1 and KM2) connected to outputs Y12 and Y13 on a Mitsubishi FXo30MR-ES PLC are used to start a motor by means of three push-buttons, PB1, PB2, and PB3, connected to inputs X10, X11 and X12 respectively. Also connected to the PLC are two indicator lamps, L1and L2 and these are connected to Y1and Y2. The circuit will operate as follow:
- When PB1 is operated, contactor KM1 will energise and start the motor in forward direction. Indicator light L1 must also light to indicate motor running forward direction;
- When PB2 is operated, contactor KM2 will energise and start the motor in reverse direction. Indicator light L2 will light to indicate motor running in reverse direction;
- PB3 when operated will stop the output currently on;
- The outputs for both contactors must not be on simultaneously. Devise an instruction list to carry out the control outlined above. Show network titles and any other information that makes the program clear. (14 marks)
Q6. (a) With the aid of a circuit diagram describe how the output port of a microprocessor may be interfaced to a motor. 6 marks (b) A thermocouple gives an output of 1mV/o^ C. Determine the minimum word length required when its output passes through an analogue-to-digital converter if temperatures from 0 to 100°C are to be measured with a resolution of 0.5°C? 6 marks (c) Draw a block diagram of a basic microcontroller and show how it may be connected to control a washing machine. 8 marks
Q7. (a) In terms of Industrial Control systems explain what is meant by:
(i) On/Off control (ii) Proportional control (iii) Integral control (iv) Derivative control In each case sketch the controllers’ output in response to an error signal. 12 marks
(b) Describe the factors that contribute to the response delay of a closed-loop system. Suggest an alternative strategy for dealing with a system where response time is critical 8 marks
