To program and test PLC ladder programs that use timer instructions. Timer Instructions of the Trainer PLC. the timer-on-delay (TON) instruction;

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1 Exercise 5 Timer Instructions EXERCISE OBJECTIVE To program and test PLC ladder programs that use timer instructions. DISCUSSION Introduction PLC timer instructions are output instructions that can be used to activate or deactivate a PLC output during definite periods of time, or in more technical terms of programmable logic, for a number of fixed time intervals. PLC timer instructions normally have three parameters: a time base, an accumulated value, and a preset value. The time base is the duration of each time interval counted by the timer instruction. With the PLC on your trainer, the time base is selectable as 0.01 s and 1.0 s. The accumulated value is the value accumulated since the timer instruction was last reset to zero. When true, the timer instruction updates the accumulated value continually. The preset value specifies the final value that the accumulated value must reach. When the accumulated value becomes equal to the preset value, the timer instruction stops timing. With the PLC on your trainer, the preset value can be set between 0 and This implies that, with a time base of 0.01 s, time delays between 0 and seconds can be obtained, and that with a time base of 1.0 s, time delays between 0 and seconds can be obtained. Timer Instructions of the Trainer PLC The PLC on your trainer includes several types of timer instructions, among which are the following: the timer-on-delay (TON) instruction; the timer-off-delay (TOF) instruction; and the retentive timer-on-delay (RTO) instruction. 5-1

2 The timer-on-delay (TON) instruction The TON instruction starts to count time base intervals when the rung in which it is contained goes from false to true. As long as the rung remains true, the TON instruction increases its accumulated value until it reaches the preset value. If the rung becomes false, the accumulated value is reset to zero regardless of whether the preset value has been reached. The timer-off-delay (TOF) instruction The TOF instruction starts to count time base intervals when the rung in which it is contained goes from true to false. As long as the rung remains false, the TOF instruction increases its accumulated value until it reaches the preset value. If the rung becomes true, the accumulated value is reset to zero regardless of whether the preset value has been reached. The retentive timer-on-delay (RTO) instruction The RTO instruction works in a way similar to that of the TON instruction: it starts to count time base intervals when the rung in which it is contained goes from false to true. As long as the rung remains true, the RTO instruction increases its accumulated value until it reaches the preset value. Contrary to the TON instruction, however, the RTO instruction retains its accumulated value if the rung becomes false. When the rung becomes true again, the RTO resumes timing starting from the accumulated value. The accumulated value of the RTO instruction is also retained if the PLC is switched from the Run mode to another mode or turned off. Another difference between the RTO and the TON instructions is that, with the RTO instruction, the accumulated value is not reset to zero when the rung becomes false. In fact, the accumulated value of an RTO instruction can only be reset by using a Reset (RES) instruction having the same address as the RTO instruction, as will be explained later in this discussion. Timer Status Bits As Table 5-1 shows, timer instructions are represented in the memory of the trainer PLC in the form of 3-word elements. Word 0 is the control word. Word 1 stores the preset value. Word 2 stores the accumulated value. Word B 15 B 14 B 13 B 12 B 11 B 10 B 9 B 8 B 7 B 6 B 5 B 4 B 3 B 2 B 1 B 0 0 EN TT DN Internal Use 1 Preset Value (PRE) 2 Accumulated Value (ACC) Table 5-1. Data file structure of timer instructions. Word 0 includes three status bits that provide important information on the timing process. These bits are the Timer Enable (EN) bit, the Timer Timing (TT) bit, and the Done (DN) bit. They are described below. 5-2

3 Timer Enable [EN] - (bit number 15 of word 0) The EN bit is set to logic state 1 when the rung containing the timer instruction is true, indicating that this instruction is true. It is set to logic state 0 when the rung is false. Timer Timing [TT] - (bit number 14 of word 0) With a TON instruction, the TT bit is set to logic state 1 when the rung of the TON instruction is true and the accumulated value is less than the preset value. It is reset to logic state 0 when the rung of the TON instruction becomes false or when the accumulated value becomes equal to the preset value (Timer DN bit set to logic state 1). With a TOF instruction, the TT bit is set to logic state 1 when the rung of the TOF instruction is false and the accumulated value is less than the preset value. It is reset to logic state 0 when the rung of the TOF instruction becomes true or when the accumulated value becomes equal to the preset value (Timer DN bit set to logic state 0). With an RTO instruction, the TT bit is set to logic state 1 when the rung of the RTO instruction is true and the accumulated value is less than the preset value. It is reset to logic state 0 when the rung of the RTO instruction becomes false or when the accumulated value becomes equal to the preset value (Timer DN bit set to logic state 1). Done [DN] - (bit number 13 of word 0) With a TON instruction, the DN bit is set to logic state 1 when the accumulated value becomes equal to the preset value, and reset to logic state 0 when the rung of the TON instruction becomes false. With a TOF instruction, the DN bit is set to logic state 1 when the rung of the TOF instruction is true, and reset to logic state 0 when the accumulated value becomes equal to the preset value. With an RTO instruction, the DN bit is set to logic state 1 when the accumulated value becomes equal to the preset value, and reset to logic state 0 when the associated Reset (RES) instruction becomes true. Using Timer Status Bits to Control Relay-Type Instructions The status bits of timer instructions (EN, TT, and DN) can be used in a ladder program to control relay-type instructions such as Examine If Closed (XIC) and Examine If Open (XIO) instructions. To do so, the address of the relay-type instruction to be controlled by a timer status bit must be entered by specifying either the number or mnemonic of this bit. 5-3

4 Addressing examples: T4:0/13 or T4:0/DN : Done bit T4:0/14 or T4:0/TT : Timer Timing bit T4:0/15 or T4:0/EN : Timer Enable bit The Reset (RES) Instruction The Reset (RES) instruction must be used to reset the accumulated value and the DN status bit of an RTO instruction after the rung containing this instruction goes false. The Reset instruction must be programmed with the same address as the RTO instruction. Procedure Summary In this exercise, you will program and test three ladder programs: one that uses a timer-on-delay (TON) instruction, one that uses a timer-off-delay (TOF) instruction, and one that uses a retentive timer-on-delay (RTO) instruction. This will allow you to understand how each of these instructions and their status bits work. Note: As earlier mentioned, the manual applies specifically to PLC Trainer Model If you are using another model, follow the exercise procedure by adapting it as described below. Model 3240-A, Model 3240-D, or Model : Same way as Model Model : Connect an external 24-VDC source to the supply jacks intended for this purpose at the left bottom of the trainer front panel. When asked to activate a PLC input, connect the corresponding PLC input jack to the positive terminal of the 24-VDC source, using a connection lead. When asked to deactivate a PLC input, remove the lead between the corresponding PLC input jack and the 24-VDC source. To determine whether or not a PLC output is activated, observe the PLC output status indicators on the PLC module. Model 9066, connect the DC COM jacks (2) to the DC SUPPLY OUTPUT negative terminal. To activate a PLC input, connect the corresponding PLC input jack to the positive terminal of the DC SUPPLY OUTPUT. To determine whether or not a PLC output is activated, you can see it on the LCD display default page (if not on this page, press ESC and select I/O status). To act on a physical device, connect VAC/VDC jacks to the positive terminal of the DC SUPPLY OUTPUT if you are are using the two first outputs or connect DC 24 + and DC 24 V - to the corresponding terminals of the DC SUPPLY OUTPUT to use last four outputs. EQUIPMENT REQUIRED Refer to the Equipment Utilization Chart, in Appendix A of this manual, to obtain the list of equipment required to perform this exercise. 5-4

5 PROCEDURE Setting Up the Equipment G 1. Connect the RS-232 serial port of the computer station to the communications port of the PLC on the PLC Trainer, using a 1761-CBL-PM02 cable. G 2. Turn on the computer and start RSLogix Micro. Turn on the PLC Trainer. G 3. In this exercise, you will study the operation of PLC instructions through observation of the ladder program view, the data files of the processor, as well as the status of the lamps next to the PLC output jacks on the trainer front panel. Note: Since trainer models and 9066 do not have output lamps, observe the PLC output status LED's on the PLC module instead. The TON Instruction G 4. Create a new project having the following processor name: EXERC_5. The project tree of processor EXERC_5 and program file LAD 2 should be displayed in the RSLogix Micro window. Program file LAD 2 contains the main ladder program. The next steps of this procedure consist in entering the ladder program of Figure

6 Figure 5-1. The timer-on-delay (TON) instruction. G 5. Select the User category of instructions by clicking the corresponding instruction category selection tab. Insert a new rung into program file LAD 2. In this rung, enter instruction XIC I:0/0. Then, enter instruction TON T4:0 by performing the following steps: Select the Timer/Counter category of instructions by clicking the corresponding instruction category selection tab. Click the Timer On-delay button on the instruction toolbar to insert this instruction in the rung, type: T4:0, then press the mouse left button to enter this address. Double-click Time Base within instruction TON T4:0. In the Time Base drop-down list that appears, select 0.01 s as the time base, then press the mouse left button to accept this selection. Double-click Preset within instruction TON T4:0, type: 1000, then press the mouse left button to accept this value. Leave the Accumulated value of instruction TON T4:0 to 0. This completes the parameter setting for instruction TON T4:0. You have now finished entering the instructions of rung 0 in the ladder program of Figure 5-1. G 6. Select the User category of instructions by clicking the corresponding instruction category selection tab. 5-6

7 Enter a new rung below the rung previously edited in program file LAD 2. In this rung, enter instruction XIC T4:0/EN. To do so, click the Examine if Closed button on the instruction toolbar, type: T4:0/EN, then click the mouse left button to enter this address. Enter instruction OTE O:0/0. You have now finished entering the instructions of rung 1 in the ladder program of Figure 5-1. G 7. Enter a new rung into program file LAD 2. In this rung, enter instruction XIC T4:0/TT, then enter instruction OTE O:0/1. You have now finished entering the instructions of rung 2 in the ladder program of Figure 5-1. G 8. Enter a new rung into program file LAD 2. In this rung, enter instruction XIC T4:0/DN, then enter instruction OTE O:0/2. You have now finished entering the instructions of rung 3 in the ladder program of Figure 5-1. G 9. Using the Verify Rung command, verify the rungs that have been edited. Correct any errors. The main ladder program in RSLogix Micro should be identical to that shown in Figure 5-1. G 10. Save the project in a project file named EXERC_5.RSS. G 11. Make sure the system communications are properly configured. G 12. Download project EXERC_5 to the PLC. Go online and place the PLC in the Run mode. G 13. Open data file T4 - TIMER. Observe that the corresponding window displays the status of the EN, TT, and DN status bits of instruction TON T4:0, as well as the time base, preset value, and accumulated value of this instruction. 5-7

8 What is the logic state of the EN, TT, and DN status bits of instruction TON T4:0? Why? Place the T4 - TIMER data file window at the bottom of the RSLogix Micro window. G 14. While observing data file T4 - TIMER and the ladder program, activate PLC input 0, using one of the toggle switches of the trainer. Does instruction TON T4:0 begin timing? Why? G 15. Once the accumulated value of instruction TON T4:0 has reached the preset value (1000), deactivate PLC input 0. Does the accumulated value return to zero? Why? G 16. While observing the accumulated value of instruction TON T4:0, activate PLC input 0 to initiate a new timing cycle. Explain what happens to the accumulated value over the next 10 seconds. G 17. Deactivate PLC input 0 to make rung 0 false. G 18. Activate PLC input 0 to initiate a new timing cycle and, while instruction TON T4:0 is timing, deactivate PLC input 0. Is the accumulated value reset to zero even though the preset value has not been reached? G Yes G No 5-8

9 G 19. Activate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the EN status bit of instruction TON T4:0 and to PLC output lamp 0 on the trainer front panel. Record your observations below and explain why this occurs. G 20. Deactivate PLC input 0. What happens to the EN status bit of instruction TON T4:0 and to PLC output lamp 0 on the trainer front panel? Why? G 21. Activate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the TT status bit of instruction TON T4:0 and to PLC output lamp 1 on the trainer front panel. Record your observations below and explain why this occurs. G 22. Deactivate PLC input

10 G 23. Activate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the DN status bit of instruction TON T4:0 and to PLC output lamp 2 on the trainer front panel. Record your observations below and explain why this occurs. G 24. Deactivate PLC input 0. What happens to the DN status bit of instruction TON T4:0 and to PLC output lamp 2 on the trainer front panel? Explain. G 25. On the PLC Trainer, make sure that all PLC inputs are deactivated. G 26. Place the PLC in the Program mode and go offline. The TOF Instruction G 27. Modify the existing main ladder program of project EXERC_5 as follows: In rung 0, replace instruction TON T4:0 with a TOF (timer-off-delay) instruction having the same address. To do so, select instruction TON T4:0 and choose the Change Instruction Type command in the contextsensitive menu. Type TOF using the keyboard and press the Enter key. (Do not modify any of the timer parameters: leave them set as they were for the TON timer studied in the previous part of the exercise.) Using the Verify Rung command, verify rung 0. G 28. Using the Save As command in the File menu, save the new ladder program in a project file named EXERC_5a.RSS. Note: Do not forget to change the processor name while you are in the Save Program As dialog box. 5-10

11 G 29. Download project EXERC_5a to the PLC of the PLC Trainer. Go online and place the PLC in the Run mode. G 30. Open data file T4 - TIMER and place the corresponding window at the bottom of the RSLogix Micro window. Is the accumulated value of instruction TOF T4:0 equal to the preset value of 1000? G Yes G No What is the logic state of the EN, TT, and DN status bits of instruction TOF T4:0? Why? G 31. While observing data file T4 - TIMER and the ladder program, activate PLC input 0, using one of the toggle switches of the trainer. What happens to the accumulated value of instruction TOF T4:0? Does this instruction begin timing? Why? G 32. Deactivate PLC input 0. Does instruction TOF T4:0 begin timing? Why? G 33. Once the accumulated value of instruction TOF T4:0 has reached the preset value (1000), activate PLC input 0. Does the accumulated value return to zero? Why? 5-11

12 G 34. While observing the accumulated value of instruction TOF T4:0, deactivate PLC input 0 to initiate a new timing cycle. Explain what happens to the accumulated value over the next 10 seconds. G 35. Activate PLC input 0 to make rung 0 true. G 36. What is the current status of the EN status bit of instruction TOF T4:0 and of PLC output lamp 0 on the trainer front panel? Why? G 37. Deactivate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the EN status bit of instruction TOF T4:0 and to PLC output lamp 0 on the trainer front panel. Record your observations below and explain why this occurs. G 38. Activate PLC input 0. What happens to the EN status bit of instruction TOF T4:0 and to PLC output lamp 0 on the trainer front panel? Explain. 5-12

13 G 39. Deactivate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the TT status bit of instruction TOF T4:0 and to PLC output lamp 1 on the trainer front panel. Record your observations below and explain why this occurs. G 40. What is the current status of the DN status bit of instruction TOF T4:0 and of PLC output lamp 2 on the trainer front panel? Explain. G 41. Activate PLC input 0. What happens to the DN status bit of instruction TOF T4:0 and to PLC output lamp 2 on the trainer front panel? Explain. G 42. Deactivate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the DN status bit of instruction TOF T4:0 and to PLC output lamp 2 on the trainer front panel. Record your observations below and explain why this occurs. 5-13

14 G 43. On the PLC Trainer, make sure that all PLC inputs are deactivated. G 44. Place the PLC in the Program mode and go offline. The RTO Instruction G 45. Modify the existing main ladder program of project EXERC_5a as indicated below to obtain the ladder program shown in Figure 5-2. a. In rung 0, replace instruction TOF T4:0 with an RTO (retentive timer-ondelay) instruction having the same address. To do so, select instruction TOF T4:0 and choose the Change Instruction Type command in the context-sensitive menu. Type RTO using the keyboard and press the Enter key. Do not modify any of the timer parameters. b. Select rung 4 (END rung) by clicking on "0004" at the left of this rung, then choose the Insert Rung command in the context-sensitive menu in order to insert a new rung before the END rung. c. In the newly created rung (rung 4), enter instruction XIC I:0/1. Then, enter instruction RES T4:0. To do so, select the Timer/Counter category of instructions by clicking the corresponding instruction category selection tab. Click the RES (reset) button on the instruction toolbar to insert this instruction in the rung, type: T4:0, then press the mouse left button to enter this address. Using the Verify Rung command, verify the rungs that have been edited. Correct the errors, if any. The main ladder program in RSLogix Micro should be identical to that shown in Figure 5-2. G 46. Using the Save As command in the File menu, save the new ladder program in a project file named EXERC_5b.RSS. Note: Do not forget to change the processor name while you are in the Save Program As dialog box. G 47. Download project EXERC_5b to the PLC of the PLC Trainer. Go online and place the PLC in the Run mode. G 48. Open data file T4 - TIMER. What is the logic state of the EN, TT, and DN status bits of instruction RTO T4:0? Why? 5-14

15 Place the T4 - TIMER data file window at the bottom of the RSLogix Micro window. Figure 5-2. The retentive timer-on-delay (RTO) instruction. G 49. While observing data file T4 - TIMER and the ladder diagram, activate PLC input 0, using one of the toggle switches of the trainer. Does instruction RTO T4:0 begin timing? Why? 5-15

16 G 50. Once the accumulated value of instruction RTO T4:0 has reached the preset value (1000), deactivate PLC input 0 to make rung 0 false. Does the accumulated value return to zero, as in the case of a TON timer instruction? Why? G 51. Leave PLC input 0 deactivated. Activate PLC input 1, using another toggle switch of the trainer. Does the accumulated value of instruction RTO T4:0 return to zero? Why? G 52. Deactivate PLC input 1. G 53. Activate PLC input 0 to initiate a new timing cycle and, while instruction RTO T4:0 is timing, deactivate PLC input 0. Observe that the accumulated value is retained. Activate PLC input 0. Does timing resume starting from the accumulated value? G Yes G No G 54. Deactivate PLC input 0. Activate PLC input 1 to reset instruction RTO T4:0, then deactivate this input. G 55. Activate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the EN status bit of instruction RTO T4:0 and to PLC output lamp 0 on the trainer front panel. Record your observations below and explain why this occurs. 5-16

17 G 56. Deactivate PLC input 0. What happens to the EN status bit of instruction RTO T4:0 and to PLC output lamp 0 on the trainer front panel? Explain. G 57. Activate PLC input 1 to reset instruction RTO T4:0, then deactivate this input. G 58. Activate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the TT status bit of instruction RTO T4:0 and to PLC output lamp 1 on the trainer front panel. Record your observations below and explain why this occurs. G 59. Deactivate PLC input 0. Activate PLC input 1 to reset instruction RTO T4:0, then deactivate this input. G 60. Activate PLC input 0 to initiate a new timing cycle. During this cycle, observe what happens to the DN status bit of instruction RTO T4:0 and to PLC output lamp 2 on the trainer front panel. Record your observations below and explain why this occurs. 5-17

18 G 61. Deactivate PLC input 0. Is the DN status bit of instruction RTO T4:0 reset to logic state 0? Why? G 62. Activate PLC input 1. What happens to the DN status bit of instruction RTO T4:0? Explain. G 63. Place the PLC in the Program mode and clear the PLC memory. G 64. Close RSLogix Micro. Turn off the computer. G 65. On the PLC Trainer, make sure that all PLC inputs are deactivated. Turn off the PLC Trainer. Remove all the switch connection leads, set all the switch toggles downward, and return all the equipment. CONCLUSION In this exercise, you familiarized yourself with timer instructions of the trainer PLC: the timer-on-delay (TON) instruction, the timer-off-delay (TOF) instruction, and the retentive timer-on-delay (RTO) instruction. You saw that these instructions have three parameters: a time base, an accumulated value, and a preset value. The TON instruction counts time base intervals when the rung in which it is contained is true. When the accumulated value reaches the preset value, the Done (DN) bit is set to logic state 1. When the rung becomes false, the accumulated value is reset to zero and the DN bit is reset to logic state 0. The TOF instruction counts time base intervals when the rung in which it is contained is false. When the accumulated value reaches the preset value, the DN bit is set to logic state 0. When the rung becomes true, the accumulated value is reset to zero and the DN bit is set to logic state 1. The RTO instruction counts time base intervals when the rung in which it is contained is true. When the accumulated value reaches the preset value, the DN bit is set to logic state 1. When the associated Reset instruction becomes true, the accumulated value is reset to zero and the DN bit is reset to logic state

19 REVIEW QUESTIONS 1. What is the time base of a timer instruction? 2. What is the preset value of a timer instruction? 3. Briefly describe the operation of the timer-on-delay (TON) instruction of the trainer PLC. 4. Are the following statements about the timer-off-delay (TOF) instruction of the trainer PLC true or false? Explain. "The TOF instruction counts time base intervals when the rung in which it is contained is false. When the accumulated value reaches the preset value, the DN bit is set to logic state 1. When the rung becomes true, the accumulated value is reset to zero and the DN bit is reset to logic state 0." 5. Explain how the TON and RTO timer instructions of the trainer PLC resemble each other and how they differ from each other in the way they work. 5-19