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 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

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.

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

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

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.

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

TON Instruction

TON stands for... zTIMER DELAY ON zTime delay period is from the instant the rung goes TRUE until the DN bit is turned on

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

TON Ladder Diagram

TON operation zWhen the rung goes TRUE, the EN and TT bits go on. zWhen the accumulated value (ACC) reaches the preset value (PRE), yTT bit goes off yEN bit stays on yDN bit turns on

TON operation (cont.) zWhen the rung goes from TRUE to FALSE and the accumulated value (ACC) is less than the preset value (PRE) yEN and TT bits turn off yAccumulated value is reset to 000 zTimer reset instructions can be used to clear ACC

TON EN bit zIs set when rung conditions are TRUE zRemains set until rung conditions go FALSE

TON TT bit zIs set when yrung conditions are TRUE AND yACC < PRE zRemains set until yrung conditions go FALSE

TON DN bit zIs set when ACC = PRE zRemains set until rung conditions go FALSE

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.

TOF Instruction

TOF stands for... zTIMER DELAY OFF zTime delay period is from the instant the rung goes TRUE to FALSE until the DN bit is turned off

TOF can be used to... zCreate longer output functions derived from short input functions; zGenerate a short pulse at the end of a long input function

TOF Timer Instruction zTOF instruction begins to count time base intervals when the rung makes a true-to-false transition. zAs long as rung conditions remain false, the timer increments its accumulated value (ACC) each scan until it reaches the preset value (PRE). zThe 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

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

TOF Ladder Diagram

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

TOF operation (cont.) zWhen the rung goes from TRUE to FALSE and the accumulated value (ACC) is less than the preset value (PRE) yDN bit stays on yTimer begins to accumulate time for the delay period yTT bit goes on and stays on for preset time, then resets zTimer reset instructions cannot be used to clear ACC

TOF EN bit zIs set when rung conditions are TRUE zRemains set until rung conditions go FALSE

TOF TT bit zIs set when yrung conditions are TRUE to FALSE AND yAC < PR zRemains set until yrung conditions go TRUE again

TOF DN bit zIs set when rung conditions are TRUE zWhen rung conditions go from TRUE to FALSE and ACC < PRE zRemains set until yACC = PRE

RTO Instruction

RTO stands for... zRETENTIVE TIMER DELAY ON zSimilar to TON zTime delay period is from the instant the rung goes TRUE until the DN bit is turned on (like TON)

RTO can be used for... zMaintenance functions; zDiagnostic programs

RTO Timer Instruction zUse the RTO instruction to turn an output on or off after its timer has been on for a preset time interval. zThe 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

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

Timer: RTO

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

RTO operation (cont.) zWhen the rung goes from TRUE to FALSE and the accumulated value (AC) is less than the preset value (PR) yEN and TT bits turn off yAccumulated value is NOT reset zTimer reset instructions must be used to clear AC

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

RTO TT bit z(like TON) Is set when yrung conditions are TRUE AND yAC < PR z(like TON) Remains set until yrung conditions go FALSE OR ywhen the DN bit is set

RTO DN bit z(like TON) Is set when AC => PR zRemains set until the appropriate RES instruction is enabled

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