 Hello everyone, welcome to this session of timers part 3. At the end of this session, you will be able to examine symbol and basic usage of off-delay timers which are available for the PLC programming. You will be also able to write ladder-run diagrams with off-delay timers for basic operations. So, let us understand more about these off-delay timers. In off-delay timers, output Q gets true immediately when input becomes true. But it will wait for a preset time PT after an input in a ladder logic becomes false before turning off the output. ET value resets on every next rising age of input. So here you will see the symbol of off-delay timer available in IAC 61131 part 3 standard having two inputs and two outputs. Let us learn more about these inputs and outputs. So input when it changes, timer starts. PT stands for preset time. The preset timer value indicates the desired delay which you want in your operation. The data type associated with input I in is Boolean means you are expecting here either zero or one whereas the data type associated with this PT preset time value is time means you have to mention your desired delay in seconds. Q here shows the output whether the time has elapsed or not. Time shows the time still remaining that is the time that has elapsed since the timer was activated. The data type associated with this Q is Boolean means you are expecting here either zero or one whereas the data type associated with this ET is time means you are expecting here the value in seconds. Let us learn the operation of off-delay timer with the help of the waveform shown on the slide. The main function of off-delay timer is to delay the falling age of output Q by predefined preset time. So here you will see that at T1 input change from 1 to 0 and after PT duration output changes from 1 to 0. So here a delay of PT value is added between the falling age of input and falling age of output. The output gets true immediately when the input condition at the timer is satisfied. So here at T0 you will see that when input changes from 0 to 1 output also changes from 0 to 1 at the same time. But timer is in still off state. At T1 instant you will see that when input changes from 1 to 0 timer starts and ET value starts incrementing towards PT value. So at T1 plus PT you will see that output changes from 1 to 0. So at T0 and T2 instant you will see that when the input changes from 0 to 1 output changes immediately from 0 to 1. Whereas at time instant T1 and T5 you will see that when input changes from 1 to 0 output will take PT duration to switch from 1 to 0. So at T1 plus PT and T5 plus PT output change from 1 to 0 respectively. After the input becomes false that is at instant T1, T3 and T5 timer starts and output will become false after preset time PT. But provided that the input has not gone true again in the meantime. So here you will see at time instant T3 input changes from 1 to 0 and at T4 input again changes from 0 to 1. So at T3 you will see that timer starts and ET value starts incrementing towards PT. But at T4 again the input value changes from 0 to 1 and ET resets to 0. So because of this this change in the input is not reflected on the output waveform. Means you have missed this change in the input on the output waveform. So let us see why this happened. So here if you compare the duration for which input is false are different. So for the output state to change from true to false the input must be false for at least as long as the preset time PT. So here you will see that between T1 and T2 the input is false for more than PT duration and because of this output is changed during this time period. Whereas during T4 and T3 you will see that the input is false for less than PT duration and this is not reflected on the output waveform. So for output state to change from true to false the input must be false for at least as long as PT duration. So this limits how you fast change your inputs. So this is the T of symbol available in open PLC editor under standard function block. Let us solve some examples with the help of off delay timer. So let us develop a ladder diagram for a system which turns on a motor when a switch is activated and keeps motor running for a predefined time let us say 5.5 seconds following the switch is deactivated. So let us see the solution for this particular example. So here you will see ladder rung is shown with input switch, output coil and off delay timer in between them and the waveform on the right hand side. Let us understand the operation of this solution with the help of waveform. So at P0 instant you will see that input 1 contact closes means input 1 changes from 0 to 1 immediately output 1 also changes from 0 to 1 means output 1 energizes. At T1 instant you will see that input 1 contact opens means here you will see that input 1 changes from 1 to 0 but here you will see output has not changed. So because of this timer starts counting with PT is equal to 5.5 seconds. So after 5.5 seconds at T2 instant you will see output 1 de-energizes. So here total 5.5 seconds delay is introduced between the falling age of input and the falling age of output. So this is one example which shows you how off delay timer can be used for controlling purpose. So let us see one example of simulation on this online PLC fiddle platform of a timer. Here you will see two rungs are there in this ladder diagram, two switches. One of the switch is timer dependent switch. Here you will see off delay timer and a motor on the right hand side. Here the preset value is set to 5.5. Let us see what happens when I change the status of switch B. So when I change the status of this switch B you will see that output motor started immediately. The accumulator value which tells you about the AT elapsed time is 0 here. Now here I will change the status of this switch B again. I will make it off. Here you will see the accumulator value that is ET value is incrementing towards 5.5. As soon as this ET becomes 5.5 your motor turns off. So this simulation shows you how a T off that is off delay timer is used to add the delay in the operation. These are the references which you can go through for further reading. Thank you.