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Timer Instructions Overview

Timer Instructions Overview. Instructions: Use the Page Up and Page Down keys to navigate through this presentation. When you are done viewing the presentation, close this window. Timers: Applications. Delay motors from starting at the same time when a switch is closed (TON Done bit)

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Timer Instructions Overview

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  1. Timer Instructions Overview Instructions: Use the Page Up and Page Down keys to navigate through this presentation. When you are done viewing the presentation, close this window.

  2. Timers: Applications • Delay motors from starting at the same time when a switch is closed (TON Done bit) • Keep track of downtime – machine is up most of the time and down sometimes (RTO ACC bit) • Open a valve for a given time after a switch is closed (e.g.,10 seconds) • Measure the cycle time of a process (RTO ACC bit) Fall 2014 - S. Hsieh

  3. Examples • Keep track of total time required to make a batch of a product (RTO ACC bit) • Turn mixing motor off 2 minutes after the switch is closed (TON – Timing bit) • Hold clamp on for 25 seconds after glue is applied after a switch is closed then open (TOF – Timing bit) • Open a valve 27 seconds after a switch is turned close. If interrupted, the valve should close and the time be reset to 0. (TON – Timing bit) Fall 2014 - S. Hsieh

  4. Categories of Timer Instructions • TON (Timer on delay) Timer remains true for a preset time interval • TOF (Timer off delay) Timer remains false for a preset time interval • RTO (Retentive timer on delay) Timer remains on for a preset time interval

  5. Parts of a Timer Instruction • Word 0: Control word • Enable bit(.EN) -- is set when the rung is true • Timer Done Bit (.DN)-- changes state when accumulated value reaches a preset value • Timer Timing bit (.TT)-- is set while the timer is incrementing its accumulated value

  6. Parts of a Timer Instruction (cont.) • Word 1: Preset Value (.PRE) • the value the timer must reach before the controller sets the DN bit. When ACC = PRE, the DN bit is set. PRE can be used to control an output device. • Word 2: Accumulated Value (.ACC) • the time elapsed since the timer was last reset. When ACC is enabled, the timer updates it continually.

  7. Parameters to Enter • Accumulated value (.ACC) • Preset value (.PRE) • Time base - the duration of each time base unit Duration of timer = (preset value - accumulator value) * time base

  8. TON Instruction

  9. TON stands for... • TIMER DELAY ON • Time delay period is from the instant the rung goes TRUE until the DN bit is turned on

  10. TON can be used to... • Create a short pulse at the beginning of a longer input condition; • Delay the start of a function for a defined period of time from the start of some other function

  11. TON Ladder Diagram

  12. TON operation • When the rung goes TRUE, the EN and TT bits go on. • When the accumulated value (ACC) reaches the preset value (PRE), • TT bit goes off • EN bit stays on • DN bit turns on

  13. TON operation (cont.) • When the rung goes from TRUE to FALSE and the accumulated value (ACC) is less than the preset value (PRE) • EN and TT bits turn off • Accumulated value is reset to 000 • Timer reset instructions can be used to clear ACC

  14. TON EN bit • Is set when rung conditions are TRUE • Remains set until rung conditions go FALSE

  15. TON TT bit • Is set when • rung conditions are TRUE AND • ACC < PRE • Remains set until • rung conditions go FALSE

  16. TON DN bit • Is set when ACC = PRE • Remains set until rung conditions go FALSE

  17. Worked Out Problems • Turn on L1 if sw1 is closed for 12 seconds. • When sw1 is closed, turn on motors 10, 11, and 12. Turn off motors 10, 11, and 12 at five-second intervals when sw1 is opened.

  18. TOF Instruction

  19. TOF stands for... • TIMER DELAY OFF • Time delay period is from the instant the rung goes TRUE to FALSE until the DN bit is turned off

  20. TOF can be used to... • Create longer output functions derived from short input functions; • Generate a short pulse at the end of a long input function

  21. TOF Timer Instruction • TOF instruction begins to count time base intervals when the rung makes a true-to-false transition. • As long as rung conditions remain false, the timer increments its accumulated value (ACC) each scan until it reaches the preset value (PRE). • The controller resets the accumulated value when rung conditions go true regardless of whether the timer has timed out Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  22. Using the TOF Status Bits • Where, the bit is set means set to 1 Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  23. TOF Ladder Diagram

  24. TOF operation • When the rung goes TRUE, the EN and DN bits go on. • When the accumulated value (ACC) reaches the preset value (PRE), • DN bit goes off • AC is reset to 000

  25. TOF operation (cont.) • When the rung goes from TRUE to FALSE and the accumulated value (ACC) is less than the preset value (PRE) • DN bit stays on • Timer begins to accumulate time for the delay period • TT bit goes on and stays on for preset time, then resets • Timer reset instructions cannot be used to clear ACC

  26. TOF EN bit • Is set when rung conditions are TRUE • Remains set until rung conditions go FALSE

  27. TOF TT bit • Is set when • rung conditions are TRUE to FALSE AND • AC < PR • Remains set until • rung conditions go TRUE again

  28. TOF DN bit • Is set when rung conditions are TRUE • When rung conditions go from TRUE to FALSE and ACC < PRE • Remains set until • ACC = PRE

  29. RTO Instruction

  30. RTO stands for... • RETENTIVE TIMER DELAY ON • Similar to TON • Time delay period is from the instant the rung goes TRUE until the DN bit is turned on (like TON)

  31. RTO can be used for... • Maintenance functions; • Diagnostic programs

  32. RTO Timer Instruction • Use the RTO instruction to turn an output on or off after its timer has been on for a preset time interval. • The RTO instruction is a retentive instruction that lets the timer stop and start without resetting the accumulated value (ACC). Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  33. Using the RTO Status Bits • To reset the ACC value and status bits, you must program a reset (RES) instruction with the same address Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  34. Timer: RTO

  35. RTO operation • (Like TON) When the rung goes TRUE, the EN and TT bits go on. • (Like TON) When the accumulated value (ACC) reaches the preset value (PRE), • TT bit goes off • EN bit stays on • DN bit turns on

  36. RTO operation (cont.) • When the rung goes from TRUE to FALSE and the accumulated value (AC) is less than the preset value (PR) • EN and TT bits turn off • Accumulated value is NOT reset • Timer reset instructions must be used to clear AC

  37. RTO EN bit • (like TON) Is set when rung conditions are TRUE • (like TON) Remains set until rung conditions go FALSE

  38. RTO TT bit • (like TON) Is set when • rung conditions are TRUE AND • AC < PR • (like TON) Remains set until • rung conditions go FALSE OR • when the DN bit is set

  39. RTO DN bit • (like TON) Is set when AC => PR • Remains set until the appropriate RES instruction is enabled

  40. Close this window and then select items 4, 5, 6 TON, TOF, and RTO Simulation.

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