SUMMER EXAMINATIONS 2014

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SUMMER EXAMINATIONS 2014 ENG302014N MODULE TITLE LEVEL TIME ALLOWED Advanced Electromechanical System Design Six Two hours Instructions to students: Enter your student number not your name on all

1 SUMMER EXAMINATIONS 2014 ENG302014N MODULE TITLE LEVEL TIME ALLOWED Advanced Electromechanical System Design Six Two hours Instructions to students: Enter your student number not your name on all answer booklets. Attempt all questions. All questions are equally weighted. Where a question has more than one part the division of marks is stated. Begin each answer on a separate page, label each page clearly with the number of the question you are answering. Graph paper and a formula booklet are provided. The use of electronic calculators of an approved type is permitted. No. of Pages 6 No. of Questions 2 Page 1 of 6

2 Answer ALL questions. 1. The schematic in Figure Q1.1 (page 3) is a signal conditioning circuit suitable for interfacing an analogue temperature sensor (LM35) to a MCU such as PICAXE 40X2. The output voltage of the sensor is directly proportional to the temperature and its sensitivity is 0.01 mv/ K. This circuit is part of an industrial controller therefore the range of temperatures considered in this application is between 0 C and 100 C. LM35 output voltage is between 0 C and 100 C and it is shown in Figure Q1.2a. a. Determine R 2 and V ref according to Figure Q1.1 (on page 3) in order to obtain a characteristic curve as shown in Figure Q1.2b (on page 3). For the analysis assume all components are ideal and R 1 is 3 kω. (HINT: The output voltage of the signal conditioning circuit is a function of Vin, Vref, R1 and R2 as shown in Figure Q1.3). (15 marks) b. If the reference voltages of the ADC are Vref-=0V and Vref+=5V, find the temperature resolution when the total number of bits during the ADC conversion process is 8 bits and 10 bits respectively. The circuit in Figure Q1.1 (page 3) is part of a water temperature control system used in an industrial tank. The controller must regulate the tank temperature according to the following requirements: 60 C (set-point) ±1.5 C (tolerance band). Water temperature is sensed using an analogue input (ADC0) and the heating element is controlled by a digital output (PICAXE 40X2 - RB0). The power rating of the heating element is 2KW and it is controlled by a relay. c. Explain a suitable temperature control algorithm. Use a flowchart or pseudocode as part of the explanation. (25 marks) QUESTIONS CONTINUE OVERLEAF Page 2 of 6

R2 VSS -10V Vref R1 V1 5 V LM35 Vs 2 3 4 8 10V U1A 1 LM358AN VCC ADC0 PICAXE 40X2 Note: The suggested

2a LM35 characteristic curve Desired output voltage of the signal conditioning circuit Q1.

3 R2 VSS -10V Vref R1 V1 5 V LM35 Vs V U1A 1 LM358AN VCC ADC0 PICAXE 40X2 Note: The suggested value for R1= 3kΩ mv Vsensor 0.01 T K K Figure Q1.1. Temperature signal conditioning circuit LM35 sensor s output voltage Figure Q1.2a LM35 characteristic curve Desired output voltage of the signal conditioning circuit Q1.2b Output voltage after signal conditioning QUESTIONS CONTINUE OVERLEAF Page 3 of 6

HINT R2 VCC -10V Vref R1 3kΩ Vin 2 3 4 8 10V U1A 1 LM358AN VSS Vo ADC0 V V R 1 V Figure Q1.

4 HINT R2 VCC -10V Vref R1 3kΩ Vin V U1A 1 LM358AN VSS Vo ADC0 V V R 1 V Figure Q1.3 R 2 2 o in ref R1 R1 LM35 Figure Q1.4. PICAXE-40X2 and LM35 pinout Total: 50 marks QUESTIONS CONTINUE OVERLEAF Page 4 of 6

5 2. The electro-pneumatic circuit in Figure Q2.1 is part of a packaging plant. The circuit has 3 pneumatic cylinders C1, C2, C3 and six end of travel switches FC1, FC2, FC3, FC4, FC5, FC6. According to Figure Q2.1, FC1, FC3, FC5 are closed when the cylinder rods are fully retracted and FC2, FC4, FC6 are closed when the cylinders are fully extended. After actuating the control switch M, the monostable valve EV1 is activated causing the cylinder C1 to extend until it reaches position FC2 moving the part upwards. When FC2 is closed and FC3 are closed, then EV2 is activated causing the cylinder C2 to extend moving the part to the right until it reaches position FC4. If FC2 is closed the valve EV1 is active for a maximum period of 5s. When FC4 and FC5 are closed the valve activation signals EV1 and EV2 are disabled while EV3 is enabled. If EV3 is enabled, cylinder C3 will extend until the part reaches its destination. At this point FC6 is closed and all the valves are in their default position (disabled). According to the functional description: a. Determine the theoretical size of (C1) when it operates at a pressure of 6bar providing a maximum force of 450N. b. Describe the components in Figure Q2.2 c. Provide an I/O table describing the electrical connections to one PLC. d. Explain the functionality of the control circuit using a flowchart. e. Implement the control strategy in ladder programming (LD). Total: 50 marks DIAGRAMS OVERLEAF Page 5 of 6

6 Figure Q2.1 Figure Q2.2 END OF PAPER Page 6 of 6

Embedded Control. Week 3 (7/13/11)

Embedded Control. Week 3 (7/13/11) Embedded Control Week 3 (7/13/11) Week 3 15:00 Lecture Overview of analog signals Digital-to-analog conversion Analog-to-digital conversion 16:00 Lab NXT analog IO Overview of Analog Signals Continuous