Page 34 - Programmable Logic Controllers, Fifth Edition

CHAPTER 1 REVIEW QUESTIONS

1. What is a programmable logic controller (PLC)? 12. The programmable controller operates in real time.
2. Identify four tasks in addition to relay switching What does this mean?
operations that PLCs are capable of performing. 13. Answer the following with reference to the process
3. List six distinct advantages that PLCs offer over control PLC ladder logic diagram of Figure 1-20 of
conventional relay-based control systems. this chapter:
4. Explain the differences between open and propri- a. What do the individual symbols represent?
etary PLC architecture. b. What do the numbers represent?
c. What field device is the number I/2 identified
5. State two ways in which I/O is incorporated into with?
the PLC. d. What field device is the number O/1 identified
6. Describe how the I/O modules connect to the pro- with?
cessor in a modular-type PLC configuration. e. What two conditions will provide a continuous
7. Explain the main function of each of the following path from left to right across the rung?
major components of a PLC: f. Describe the sequence of operation of the
a. Processor module (CPU) controller for one scan of the program.
b. I/O modules 14. Compare the method by which the process control
c. Programming device operation is changed in a relay-based system to the
d. Power supply module method used for a PLC-based system.
8. What are the two most common types of PLC 15. Compare the PLC and PC with regard to:
programming devices? a. Physical hardware differences
9. Explain the terms program and programming b. Operating environment
language as they apply to a PLC. c. Method of programming
10. What is the standard programming language used d. Execution of program
with PLCs? 16. What two categories of software written and run on
11. Answer the following with reference to the process PCs are used in conjunction with PLCs?
control relay ladder diagram of Figure 1-17 of this 17. What is a programmable automation controller
chapter: (PAC)?
a. When do the pressure switch contacts close? 18. List four criteria by which PLCs are categorized.
b. When do the temperature switch contacts close? 19. Compare the single-ended, multitask, and control
c. How are the pressure and temperature switches management types of PLC applications.
connected with respect to each other?
d. Describe the two conditions under which the 20. What is the memory capacity, expressed in bits, for
motor starter coil will become energized. a PLC that uses 16-bit words and has an 8 K word
e. What is the approximate value of the voltage capacity?
drop across each of the following when their 21. List five factors affecting the memory size needed
contacts are open? for a particular PLC installation.
(1) Pressure switch 22. What does the instruction set for a particular PLC
(2) Temperature switch refer to?
(3) Manual pushbutton

Programmable Logic Controllers (PLCs) Chapter 1 15

pet73842_ch01_001-016.indd 15 03/11/15 7:09 PM