Download Exam Questions: Electro-Technology and Control for Mechanical Engineering Students and more Exams Electrical Engineering in PDF only on Docsity! Cork Institute of Technology Bachelor of Engineering in Mechanical Engineering - Award Bachelor of Engineering in Manufacturing Engineering - Award (EMECH_7_Y3) (EMANF_7_Y3) Summer 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 Question 1 The following loads are connected to a 3-phase 4-wire 400 V/230 V supply: Between Brown line and Neutral: 13 kW @ 0.92 p.f. Between Red line and Neutral: 9 kW @ 0.80 p.f. Between Yellow line and Neutral: 11 kW @ 1.0 p.f. (a) Draw a fully detailed circuit diagram representing the load. Show all values. (6 Marks) (b) Calculate the current and phase angle for each phase. (6 Marks) (c) Determine by vector diagram or otherwise, the current in the neutral conductor. (8 Marks) 2 Question 2 (a) A 3-phase, 12kW, 400V, 50Hz, 4-pole, delta connected squirrel cage induction motor has a full-load; efficiency of 78%, power factor of 0.75, and running speed of 1440 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. (12 Marks) (b) Explain the terms; synchronous-speed and slip of a 3-phase motor. (2 Marks) (c) Star-Delta starting is a method of induction motor starting that is used to reduce starting currents. Prove how the starting current is reduced to 1/3 using this method of starting using a motor of winding resistance 40Ω connected firstly in Star and then Delta to a 400V Supply. (6 Marks) Question 3 (a) The Mitsubishi FXo30MR-ES PLC contains both Counters and Timers. How many Timers and Counters are contained with the PLC and give an example of each. (3 Marks) (b) When specifying a timer a value K must be supplied to define the length of the timer. What is the resolution of the value of K, i.e. how long is K = 1. (3 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 two push-buttons; PB1, PB2 and PB3 connected to inputs X10, X12 and X1 respectively. Also connected to the PLC are two indicator lamps, L1and L2 and these are connected to Y4 and Y7 and a NO contact is connected from the contactor to X15. The circuit will operate as follow: 5 Section B (Control Technology) Please Use Answer Book B Q5. (a) With the aid of a diagram, describe the architecture of a Programmable Logic Controller. [10 marks] (b) In a press application, a pneumatic double-acting cylinder is driven by a valve having two solenoids, one for extend and one for retract. The cylinder can extend if it is situated in the UP position, a Protective Barrier is in place and the Extend push-button is depressed. It then extends fully and remains in this position for 10 seconds, whereupon it retracts automatically. The cylinder is also to retract if, during a press operation, the protective barrier is disturbed. Develop a solution using a ladder diagram. [10 marks] Q6. (a) With the aid of a Karnaugh map reduce the following switching function to its simplest form: 1 ( , , , )A B C D ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD G = + + + + + + + [5 marks] (b) A thermocouple gives an output of 0.2 mV/ºC. Its output passes through an analogue-to-digital converter. Temperatures from 0ºC to 200ºC 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] 6 Q7. (a) List FIVE features of I/O bus networks. [5 marks] (b) Draw a block diagram of a typical intelligent field device, labelling each section. [5 marks] (c) Describe the general components of a SCADA Interface. [10 marks]
