This article discusses about OFF delay timer instruction and its working principle using Allen Bradley Programmable Logic Controller (PLC) Ladder Logic.
Timer OFF delay is to delaying the turning OFF of any output, Example-Setting timer to turn off Induction Stove, TV remote settings to turn OFF TV after certain time.
OFF Delay Timer
In the above OFF delay timer instruction, there are totally four parameter,
TIMER: T4:0 – Timer File name (Timer T4:0, T4:1, T4:2…)
TIMER BASE – How the time need to count, in Seconds, Milli Seconds.
PRESET – Limit value of Timer-Up to how much it should count
ACCUMULATOR – Running Value of timer when it is in ON condition.
Off- delay timer instructions is used to program a time delay to begin after rung input goes false.
As an example, when an external cooling fan on a motor is provided, the fan has to run all the time the motor is running and also for certain time (say 10 min) after the motor is turned off. This is a ten minute off- delay timer. The ten-minute timing period begins as soon as the motor is turned off.
OFF Delay Timer using PLC
RUNG 0000 :
Start/ Stop Switch is to turn ON/OFF the timer.
RUNG 0001 :
When start switch is pressed, Timer Enable bit (T4:0/EN) is turned ON to show the status of TIMER ON/OFF condition along with timer done bit (T4:0/DN)
RUNG 0002 :
When Start/Stop switch is Turned OFF, timer enable bit, timer timing bit turned OFF to show the status of timer. Timer Timing bit turned ON to show the status of timer is running. Time done bit maintain its previous state.
RUNG 0003 :
If accumulator value reaches preset value, all the timer bits (EN,TT & DN) are turned off.
We can use this example program to understand the working of OFF delay timer function in Allen Bradley PLC.