Help!! Control and Automation problems

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1. What are the difference between relay circuit and PLC circuit?
2. What are the 4 classes of programming languages of PLC?
3. How to illustrate the meaning of control system in control and automation system?
4. How to illustrate the major role of CPU in a PLC and what is the major role of CPU?

5. How to illustrate the major role of volatile memory and non-volatile in a PLC and what is the major role of volatile memory and non-volatile?

6. An on-off controller is used to control the temperature of a process. The cycling amplitude is reduced by making the two heating rates very close to average required for normal operation. What are the disadvantages on this set up?

[qpzm77gg]

Q2. switch level, Gate level, Behavioral level ???? Is't correct?
Q3. How to illustrate?? I still not know
Q4. The function of CPU in PLC are communication with the memory, perform logic and arithmetic operations, updating the inputs and outputs. Is't correct?? Besides, how to illustrate that?
Q5. PLC uses a volatile memory with a backup battery. PLC uses a non-volatile memory for frequently used for a particular application and required faster setup.
Correct or wrong?

Thanks a lot.

Edited May 13, 2013 by qpzm77gg