Page 62 - Programmable Logic Controllers, Fifth Edition

CHAPTER 2 REVIEW QUESTIONS

1. What is the function of a PLC input interface a. What is the maximum current rating for a typical
module? 120 VAC output module?
2. What is the function of a PLC output interface b. Explain one method of handling outputs with
module? larger current requirements.
3. With reference to a PLC rack: 21. What electronic element can be used as the switch-
a. What is a remote rack? ing device for DC discrete output modules?
b. Why are remote racks used? 22. A discrete relay type output module can be used to
4. How does the processor identify the location of a switch either AC or DC load devices. Why?
specific input or output device? 23. With reference to sourcing and sinking I/O modules:
5. List the three basic elements of rack/slot-based a. What current relationship are the terms sourcing
addressing. and sinking used to describe?
b. If an I/O module is specified as a current-sinking
6. Compare bit level and word level addressing.
type, then which type of field device (sinking or
7. In what way does tag-based addressing differ from sourcing) it is electrically compatible with?
rack/slot-based addressing?
24. Compare discrete and analog I/O modules with
8. What do PC-based control systems use to interface respect to the type of input or output devices with
with field devices? which they can be used.
9. What type of I/O modules have both inputs and 25. Explain the function of the analog-to-digital (A/D)
outputs connected to them? converter circuit used in analog input modules.
10. In addition to field devices, what other connections 26. Explain the function of the digital-to-analog (D/A)
are made to a PLC module? converter circuit used in analog output modules.
11. Most PLC modules use plug-in wiring terminal 27. Name the two general sensing classifications for
strips. Why? analog input modules.
12. What are the advantage and the disadvantage of 28. List five common physical quantities measured by
using high-density modules? a PLC analog input module.
13. With reference to PLC discrete input modules: 29. What type of cable is used when connecting a ther-
a. What types of field input devices are suitable for mocouple to a voltage sensing analog input mod-
use with them? ule? Why?
b. List three examples of discrete input devices. 30. Explain the difference between a unipolar and bi-
14. With reference to PLC discrete output modules: polar analog input module.
a. What types of field output devices are suitable
for use with them? 31. The resolution of an analog input channel is speci-
b. List three examples of discrete output devices. fied as 0.3 mV. What does this tell you?
15. Explain the function of the backplane of a PLC 32. In what two ways can the loop power for current
rack. sensing input modules be supplied?
16. What is the function of the optical isolator circuit 33. List three field devices that are commonly con-
used in discrete I/O module circuits? trolled by a PLC analog output module.
17. Name the two distinct sections of an I/O module. 34. State one application for each of the following
special I/O modules:
18. List four tasks performed by a discrete input a. High-speed counter module
module. b. Thumbwheel module
19. What electronic element can be used as the switch- c. TTL module
ing device for a 120 VAC discrete output interface d. Encoder-counter module
module? e. BASIC or ASCII module
20. With reference to discrete output module current f. Stepper-motor module
ratings: g. BCD-output module

PLC Hardware Components Chapter 2 43

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