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) 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

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

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

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

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.

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

TON Instruction

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

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

TON Ladder Diagram

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

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

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

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

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

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.

TOF Instruction

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

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

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

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

TOF Ladder Diagram

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

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

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

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

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

RTO Instruction

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)

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

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

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

Timer: RTO

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

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

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

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

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

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