PART 3 REVIEW QUESTIONS 1. Compare the methods used to address timers in an SLC 500 and a ControlLogix controller. 2. List the five different members of a TIMER structure. 3. What type of timing application may require you to use a TON on-delay timer? 4. What PRE value is used for a timer? 5. To what value is the accumulated value of a timer normally set? 6. What timer status bit is set to 1 when the TON timer times out? 7. The TON instruction is self-resetting. Explain what this means. 8. What number would be entered into the PRE value of a ControlLogix timer for a timing period of 4.5 minutes? 9. Compare the operation a TOF and a TON timer. 10. When does the rung of a TOF timer begin accumulating time? 11. The RTO timer is a retentive timer. Explain what this means. 12. How are the retentive timer and reset instruction related? PART 3 PROBLEMS 1. Modify the original CLX ten-second TON timer program (Figure 15-52) with an additional rung added to the program that will energize a solenoid whenever the timer is enabled and timing. The solenoid is to be connected to pin 6 of the digital output module. 2. With reference to the ladder logic of the CLX diverter gate program (Figure 15-53), assume the solenoid gate fails to energize as programmed. You suspect the problem is due to an open in the solenoid coil or wiring to it. How might observation of the solenoid output status light help confirm this? 3. You are required to extend the Green light-on time of the CLX traffic control program (Figure 15-55) to 40 seconds. What changes would have to be made to the program? 4. With reference to the CLX heating oven process program (Figure 15-59), assume the oven-on pilot light burns out. In what way would the operation of the program be affected? 5. With reference to the CLX limit switch RTO program (Figure 15-62), in addition to the alarm, you are required to install a warning pilot light to indicate that the timer has timed out. How would you proceed? 6. Implement the hardwired TON alarm circuit of Figure 15-66 in Logix format. L1 L2 ON/OFF switch CR TR CR switch On-delay timer 10 s Low pressure TR Alarm Figure 15-66 Hardwired TON alarm circuit for Problem 6. Programming Timers Part 3 367
Petruzella_ProgrammableLogicControllers__5e
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