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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. Timer Applications. Delay motors from starting at the same time Keep track of downtime

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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. Timer Applications • Delay motors from starting at the same time • Keep track of downtime • Open a valve for a given time (e.g.,10 seconds) • Measure the cycle time of a process Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  3. Practical Examples • Keep track of total time required to make a batch of a product • Turn mixing motor off 2 minutes after the switch is closed • Hold clamp on for 25 seconds after glue is applied • Open a valve 27 seconds after a switch is turned on. If interrupted, the valve should close and the time be reset to 0. Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  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 Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  5. Timer: TON Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  6. Timer: TOF Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  7. Timer: RTO Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  8. 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 Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  9. 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. Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  10. 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. Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  11. 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 Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  12. Think about... • How would you write a program to control these processes? • Your factory has a machine with a large steel shaft supported by three journal type, babbitted bearings. This shaft is coupled to a large electric motor. The bearings need lubrication, which is supplied by an oil pump driven by a small electric motor. • To start the machine, the operator must turns sw0 on. Before the shaft starts to turn, the bearings must receive oil for 10 seconds. When the operator turns sw0 off to stop the machine, the oil pump continues to supply oil for 15 seconds. Sheng-Jen (“Tony”) Hsieh, Texas A&M University

  13. Close this window and then select item 2, Overview Practice Sheng-Jen (“Tony”) Hsieh, Texas A&M University

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