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

Sheng-Jen (“Tony”) Hsieh, Texas A&M University Practical Examples zKeep track of total time required to make a batch of a product zTurn mixing motor off 2 minutes after the switch is closed zHold clamp on for 25 seconds after glue is applied zOpen 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 Categories of Timer Instructions zTON (Timer on delay) Timer remains true for a preset time interval zTOF (Timer off delay) Timer remains false for a preset time interval zRTO (Retentive timer on delay) Timer remains on for a preset time interval

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

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

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

Sheng-Jen (“Tony”) Hsieh, Texas A&M University Parts of a Timer Instruction zWord 0: Control word yEnable bit(.EN) -- is set when the rung is true yTimer Done Bit (.DN)-- changes state when accumulated value reaches a preset value yTimer Timing bit (.TT)-- is set while the timer is incrementing its accumulated value

Sheng-Jen (“Tony”) Hsieh, Texas A&M University Parts of a Timer Instruction (cont.) zWord 1: Preset Value (.PRE) ythe 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. zWord 2: Accumulated Value (.ACC) ythe 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 Worked Out Problems zTurn on L1 if sw1 is closed for 12 seconds. zWhen 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 Parameters to Enter zAccumulated value (.ACC) zPreset value (.PRE) zTime 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 Think about... zHow would you write a program to control these processes? yYour 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. yTo 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.

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