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Cork Institute of Technology
Bachelor of Engineering in Mechanical Engineering – Award
Bachelor of Engineering in Manufacturing Engineering - Award
(EMECH_7_Y3) (EMANF_7_Y3)
Autumn 2008
ELECTRO-TECHNOLOGY AND CONTROL
(Time: 3 Hours)
INSTRUCTIONS: Answer Five Questions, at least Two from each section. All formula and calculations must be shown.
Examiners: Mr. N. Mulcahy Mr. M. Murray Mr. A. Bateman Dr. P. Delassus
Section A ( Electro-technology )
Please Use Answer Book A
Q
The following single-phase 400V loads are connected across a 3-phase, 3-wire, 400V supply: (i) Between Brown and Red lines 15 kW at 0.88 p.f. lagging; (ii) Between Red and Yellow lines 11 kW at 1.0 p.f. lagging; (iii) Between Yellow and Brown lines 17 kW at 0.87 p.f. lagging.
(a) Draw a circuit diagram showing the loads above as seen by a 3-phase supply and calculate each phase current and its phase angle. 6 marks
(b) Draw a vector diagram showing the supply voltages and the phase currents drawn to scale. 6 marks
(c) Calculate, or determine by means of a vector diagram, the current in each supply line. 8 marks
Q
(a) Explain the terms; synchronous-speed, slip-speed, and slip of a 3-phase induction motor. (6 marks) (b) Calculate for a 6-pole, 50 Hz motor with a full-load slip of 2.5%: (i) The synchronous speed in R.P.M; (ii) The full-load speed in R.P.M. ( 4 Marks)
(c) The motor in (b) has a full-load rating of 18.5kW at 400 V. If the full load efficiency and power factor are 87.2% and 0.74 respectively, calculate: (i) Input power; (ii) Supply current; (iii) Full-load torque. (10marks)
Q3 (a) Detail the number of counters and timers contained within the Mitsubishi FXo30MR-ES PLC. (4 marks)
(b) Give an example address of a timer and specify the value of K required which provides a time delay of 3.5 seconds. (2 marks)
(c) Two contactors (KM1 and KM2) connected to outputs Y12 and Y13 on a Mitsubishi FXo30MR-ES PLC are used to start two separate motors (M1 and M2) by means of two push-buttons, PB1and PB2, connected to inputs X10, 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 (M1). Indicator light L1 must also light to indicate motor M1 is running;
- Ten seconds after M1 has been energised, contactor KM2 will energise and start the Motor M2. Indicator light L2 will light to indicate motor M2 is running;
- PB2 when operated will stop both Motors; No thermal overload has been used in the circuit.
StartForw ard
F1Fuse ControlCircuit
Stop
KM1 KM
KM1N/O KM1N/O
Timer
Run LampM1 Run LampM
KA
KA1N/O
F Fuse ControlCircuit
3 ~M
KM
3 ~M
KM
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 Karnaugh map reduce the following switching function to its
simplest form:
G 1 ( A , B , C , D )= ABCD + ABCD + ABCD + ABCD + ABCD + AB^ CD
[5 marks]
(b) A thermocouple gives an output of 0.5 mV/ºC. Its output passes through an analogue-to-digital converter. Temperatures from 0ºC to 400ºC are required to be measured with a resolution of 0.1ºC? What word length is required for the A/D converter? [5 marks]
(c) Explain the operation of the following circuit; use a timing diagram and truth table as appropriate.
[10 marks]
Q7. (a) Explain what is meant by the term I/O bus networks. [5 marks]
(b) List FIVE advantages of I/O bus networks. [5 marks]
(c) Describe FOUR features of a SCADA Interface. [10 marks]
