1.6 PRACTICE PROBLEMS

1. PLC’s typically contain:

a) EPROM

b) Battery

c) Both a) and b)

d) None of the above

2. A PLC can only go through the ladder logic a few times per second. Why?

3. Indicator lights are used on PLC’s for,

a) maintenance

b) diagnostics

c) a) and b)

d) none of the above.

(ans. c)

8. What will happen if the scan time for a PLC is greater than the time for an input pulse? Why?

(ans. the pulse may be missed if it occurs between the input scans)

11. What is the difference between a PLC and a desktop computer?

19. Why do PLCs do a self check every scan?

4. TRUE or FALSE -- The test time for a PLC will be long compared to the time required for a simple program.

(ans. true)