Page 321 - Programmable Logic Controllers, Fifth Edition - Mobile version

CHAPTER 13 REVIEW QUESTIONS

1. Why are PLCs installed within an enclosure? 16. List four uses for the data monitor function.
2. What methods are used to keep enclosure 17. What information is provided by the cross refer-
temperatures within allowable limits? ence function?
3. State two ways in which electrical noise may be 18. What information is provided by the contact
coupled into a PLC control system. histogram function?
4. List three potential noise-generating inductive 19. List five preventive maintenance tasks that should
devices. be carried out on the PLC installation regularly.
5. Describe four ways in which careful wire routing 20. Outline the general procedure followed to lock out
can help cut down on electrical noise. and tag a PLC installation.
6. a. What type of input field devices and output 21. Typically, what does each of the following proces-
modules are most likely to have a small sor diagnostic light states indicate?
leakage current flow when they are in the off a. RUN light is off.
state? Why? b. Fault light is off.
b. Explain how an input bleeder resistor reduces c. BATTERY light is on.
leakage current. 22. Explain the function of a watchdog timer circuit.
7. Summarize the basic grounding requirements for a 23. A PLC is operating in the RUN mode but output
PLC system. devices do not operate as programmed. List five
8. Under what condition can a ground loop circuit be faults that could be responsible for this condition.
developed? 24. What is the verify results function used for?
9. When line voltage variations to the PLC power 25. A fast-acting solenoid-operated gate is suspected
supply are excessive, what can be done to solve the of not functioning properly when energized and de-
problem? energized by the PLC program. Explain how you
10. What operating state will cause an inductive load to would use the force function to check its operation.
generate a very high voltage spike? 26. What happens when the processor encounters a
11. Explain how a diode is connected to suppress a DC temporary end instruction?
inductive load. 27. Explain the function of the suspend instruction.
12. Explain how an MOV suppresses an AC inductive 28. In what negative ways can faulty wiring and connec-
load. tions affect signals sent to and from the I/O modules?
13. What is the purpose of PLC editing functions? 29. The same address is used for two coil instructions
14. What is involved with commissioning a PLC within the same PLC program. What will happen as
system? a consequence of this?
15. a. Compare offline and online programming. 30. Compare the uses for RSLogix and RSLinx
b. Which method is safer? Why? programming software.

CHAPTER 13 PROBLEMS

1. The enclosure door of a PLC installation is not kept 3. Whenever a crane located over a PLC installation is
closed. What potential problem could this create? started from a standstill, temporary malfunction of
2. A fuse is blown in an output module. Suggest two the PLC system occurs. What is one likely cause of
possible reasons why the fuse blew. the problem?

302 Chapter 13 PLC Installation Practices, Editing, and Troubleshooting

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