Page 392 - Programmable Logic Controllers, Fifth Edition - Mobile version

PART 4 REVIEW QUESTIONS

1. In what way are timers and counters similar? 6. Compare the operations of a CTU and a CTD
2. Outline the procedure followed to create a tag when counter.
you want to use a counter. 7. What is an Up/Down counter?
3. All counters are retentive. In what way does this af- 8. Explain how you go about creating tags for an Up/
fect their operation? Down counter that uses a CTU and CTD instruction.
4. What is specified by the preset value of a counter?
5. When is each of the following counter bits set?
a. CU
b. DN
c. CD

PART 4 PROBLEMS

1. With reference to the CTU packets of bottles pro- 4. Write a ControlLogix program, complete with tags,
gram (Figure 15-70), what changes to the program for an Up/Down counter used to keep track of cars
would be required to count six bottle packets? entering and exiting a parking lot. The program re-
2. With reference to the CTU program used to remove quirements for this application can be summarized
containers from a conveyor line (Figure 15-71), as- as follows:
sume the output solenoid coil failed open. In what • The parking lot holds 30 vehicles.
way would the operation of the program be affected? • There is an entrance vehicle sensor and an exit
vehicle sensor.
3. Modify the original Up/Down counter program
(Figure 15-74) to include: • When the parking lot is full a Lot Full sign is
a. A red pilot light to indicate entry of a part into the illuminated.
buffer zone. Light to be connected to pin 4 of the • Whenever a car exits the lot, a Caution Buzzer/
digital output module. Light is activated to warn pedestrians.
b. A green pilot light to indicate exit of a part from
the buffer zone. Light to be connected to pin 3 of
the digital output module.

Programming Counters Part 4 373

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