PART 4 REVIEW QUESTIONS 1. In what way are timers and counters similar? 2. Outline the procedure followed to create a tag when you want to use a counter. 3. All counters are retentive. In what way does this affect their operation? 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 program (Figure 15-70), what changes to the program would be required to count six bottle packets? 2. With reference to the CTU program used to remove containers from a conveyor line (Figure 15-71), assume the output solenoid coil failed open. In what way would the operation of the program be affected? 3. Modify the original Up/Down counter program (Figure 15-74) to include: a. A red pilot light to indicate entry of a part into the buffer zone. Light to be connected to pin 4 of the digital output module. 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. 6. Compare the operations of a CTU and a CTD counter. 7. What is an Up/Down counter? 8. Explain how you go about creating tags for an Up/ Down counter that uses a CTU and CTD instruction. 4. Write a ControlLogix program, complete with tags, for an Up/Down counter used to keep track of cars entering and exiting a parking lot. The program requirements for this application can be summarized as follows: • The parking lot holds 30 vehicles. • There is an entrance vehicle sensor and an exit vehicle sensor. • When the parking lot is full a Lot Full sign is illuminated. • Whenever a car exits the lot, a Caution Buzzer/ Light is activated to warn pedestrians. Programming Counters Part 4 373
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