Control and Automation Exam for Bachelor of Engineering in Electrical Engineering, Exams of Control Systems

Download Control and Automation Exam for Bachelor of Engineering in Electrical Engineering and more Exams Control Systems in PDF only on Docsity! Cork Institute of Technology Bachelor of Engineering in Electrical Engineering – Award (EELEC_7_Y3) Autumn 2008 Control & Automation (Time: 3 Hours) INSTRUCTIONS: Answer Five Questions, at least Two from each section. All formula and calculations must be shown. Examiners: Mr. R. Daly Mr. P. O Murchu Prof. E. Mc.Quade Mr. M. Hennessy Section A (Control) Please use answer book A! Q1 (a) Given that the circuit voltages in Fig. 1 below can be represented by the following equation; ∫ ++= idt Cdt diLRitVi 1)( Show that the system transfer function can be given by the following equation; LC s L Rs LC sV sV i o 1 1 )( )( 2 ++ = (10 Marks) (b) Given that the value of the circuit components are as follows; R=125Ω, L=12.5H, C=400µF, evaluate the system transfer function and show the location of the system poles and zeros on the s-plane. (10 Marks) Fig. 1 i )(tVi )(tVo L R C 2 Q2 (a) Evaluate the closed loop transfer function of the circuit shown in Fig. 2 below. (5 Marks) (b) The system is now subjected to a unity step input. Plot the output response of the system in the time domain. (15 Marks) Q3 (a) Evaluate the closed loop transfer function of the circuit shown in Fig. 3. (5 Marks) (b) Determine the values of KP and KI so that the system is critically damped with a settling time of 2.5 seconds, when subjected to a unity step input. (15 Marks) Take : TS = 4.6 ωn + _ s KK IP + 4 5 +s R(s) Y(s) Fig. 3 25 14 40 +s 0.35 + _ R(s) Y(s) Fig. 2 5 Section B (Automation) Please Use Answer Book B Q5. (a) Show by means of a single Ladder PLC network, the instructions for a motor start/stop control using the output address as the latching element. Explain the potential hazards of this design and the modification that needs to be made to rectify the program. (3 Marks) (b) A contactor switched by the modified program in (a) latches when the contactor actuator is operated manually. Show how the programmed solution might be further modified to prevent this manual latching and explain how the modification achieves this. (3 Marks) (c) Two motors are to be controlled by means of a Siemens S7-200 PLC to operate as follows: Motor 1 is to be started in either forward or reverse direction by means of push-button control. Motor 2 must start automatically 20 seconds after motor 1 starts and is to stop automatically 15 seconds after Motor 1 is stopped. Indication lamps are used to indicate motor running direction and motor tripped. Show a symbol table for input devices, output devices, timers, memories, etc. (4 Marks) (d) Develop a program for the control outlined in (c) showing; network titles, input and output addresses, input and output symbol names and comments where appropriate. The lamp to indicate motor tripped must be flashed at 1 Hz. (10 Marks) 6 Q6. (a) Show by means of a clearly labelled diagram, the steps involved in measuring a physical analog quantity, connecting its signal to a PLC analog input module, and converting the signal level to a 15-bit binary value. The data representing the analog signal is to be stored in a dedicated 16-bit address in memory. (6 Marks) (b) Explain the use of bit-16 in the converted analog data in (a) (2 Marks) (c) A –10V/0V/+10V bipolar analogue input to a PLC is converted to a 16-bit binary value. Given that bit-15 is a sign bit, determine the range of values represented by the analog input and the corresponding stored value and binary representation for the following voltages on the inputs: (i) +5.6V; (ii) –7.8V. (All steps must be shown in determining the binary representations) (8 Marks) (d) Write the hexadecimal equivalent of the stored binary strings for the calculated values in (c) above (4 Marks) Q7. (a) Draw a motor power circuit for a reversing motor starter to include: (i) Source of isolation with short-circuit protection; (2 Marks) (ii) Interconnected motor contactors and overload unit; (6 Marks) (iii) Local motor isolator; (2 Marks) Use IEC standard referencing and labelling throughout. (b) Show by means of a connection diagram, how the push buttons, overload relay contacts, contactor replies, contactor coils, indication lamps, etc, for the starter are terminated at a Siemens S7-200 PLC. (10 Marks) 7 Q8. (a) List two types of proximity and photoelectric sensors commonly used in industry and give one application of each. (4 Marks) (b) Describe three types of actuators that can be switched by the digital outputs of a programmable controller. List some of the typical standard operating voltages, and the type of force that causes the final action. (6 Marks) (b) Proximity sensors and photoelectric sensors can be selected for either sink or source PLC input modules. Explain what is meant by the terms sink and source and which type of switched output is required from the sensors in each case. (4 Marks) (c) List the three types of switching used in PLC output modules and indicate the factors that would influence your selection of each type. (6 Marks)