 Hello everyone, welcome to this session on timers, PLC timers. So at the end of the session you will be able to examine symbols, basic usage and types of timers which you can use in PLC programming. You will be also able to write simple ladder run diagrams with pulse timers for basic operations. So let us learn about the timers, what are the timers. So timers are normally used to control a task with reference to time. Timers counts seconds or fraction of seconds using the internal CPU clock. These timers are already predefined as a standard function blocks in ISE 61131 part 3 standard. So a symbol is shown. Here you will see a typical timer comes with two inputs with two outputs. Multiple timers can be linked together which is also called as a cascaded together to get larger delays. Timers are able to change the state of Boolean addresses at a desired time after some criteria has been made. Timers allows multitude of operations in a control circuit to be automatically started and stopped at different time intervals. So depending upon your automation you can use these timers for your task control. Parameters of timers used in a circuit can be increased or decreased through the use of programming changes rather than wiring changes. So in old days you will find that there are some mechanical and electrical timers were available for controlling the process automations. So as compared to them these timers which are available in PLCs are easily programmable. Accuracy and repeatability of the timers are extremely high because timer delays are generated in the PLC processors. We already know that PLCs are designed with the help of different microcontrollers or microprocessors. So the features which that microcontroller or microprocessor provides they are available in the PLCs also. So one of the features is the timer which we already know that we have different timers in the microcontrollers. Let us learn about the timer inputs. So here on this function block you will see that there are two inputs represented with IN and PT names. So in when this input changes its state the timer starts counting towards the preset time. The data type associated with this IN input is Boolean means you are expecting here either 0 or 1. Second input is the PT. PT stands for preset time. So this preset timer value indicates the desired delay which you want in your operation. The data type associated with this PT is time means you have to mention the desired delay in terms of seconds. Timer outputs so here you have two outputs Q shows whether the time has elapsed or not the data type associated with this Q is Boolean means you are expecting either 0 or 1 on this line. Second output is the ET. ET stands for elapsed time. So this ET shows the time still remaining that is the time that has elapsed since the timer was activated. Timer outputs can be checked at any point in the program are always updated with the current values of the physical timer running in the background. There are two approaches we can use these timers in the ladder diagram programming or in any other programming interface. First approach you can consider the timers like relays with coils. So here you will see that in a first run a timer is shown as a relay coil symbol. When these coils gets energized the results in the closure or opening of the contacts after some preset time. So here you will see that in the second run a timer contact is shown this timer contact is dependent contact it depends on the status of this timer. When this timer contacts gets activated because of this timer you will get your output energized. So this is the first approach. In the second approach you can consider timers as a delay block means you can insert the timer in a rung as shown in this figure. What this timer does it adds a delay because of that signal in the rung from reaching the output gets delayed. So this is the second approach which you can apply for using the timer in your simple ladder runs. Let us go through the timer types these are the basic timers available in any small PLCs. First one is the pulse timer second is the on delay timer and third one is the off delay timer. Let us learn more about the pulse timer in this particular session. So pulse timers you can use as a pulse generator they generates a pulse of fixed duration and the duration of that pulse is Pt that is defined by the preset time. You will get this pulse at the output queue on the rising age of the input applied. So here the function block shows how a typical pulse timer looks like. So here you have two inputs in and Pt and two outputs Q and Et. Let us understand the operation of pulse timer with the help of waveforms. So output state of a pulse timer changes from false to true when the input changes from false to true that is on the rising age of the input. So here at a t0 instant you will see that input changed from 0 to 1. At the same time you will see that timer output Q also changed from 0 to 1. And the output will remain true for the preset time Pt. So here you will see that this output remain true up to t0 plus Pt. So the pulse width of this Q at this particular instant is Pt duration. For the output state to change from false to true the input rising ages must be apart from at least as long as the preset time. So here at t2 instant you will see that input changed from 0 to 1. At the same time output also changed from 0 to 1. And timer started from incrementing from 0 towards Pt. So Et value you will see that is incrementing from 0 onwards towards Pt. But at t3 you will see that input again changed from 0 to 1. Now the difference between t3 and t2 is less than Pt. And because of this this change at t3 will not be reflected on your Q output. Meaning this t3 input change at t3 is missed by your PLC. So because of that the difference between two rising ages of the input must be Pt time apart. So when your input changes from 1 to 0 you will see that Et also resets to 0. So at the time instant t1 and t5 you will see that Et resets to 0. So when the duration of Pt is reached that is Et becomes Pt and the signal state at input is false Et output resets. So here at t1 then t2 plus Pt and at t5 you will see that Et resets to 0. So this is a typical pulse timer symbol available in an open PLC editor under standard function block library. Let us solve one example. Let us develop a ladder diagram for a system that will run a motor for a predefined fixed length of time when the input switch is activated. You can take some time and you can develop a ladder diagram for this particular problem. So this is the solution you will see here a rung is shown in which a switch is used along with the motor and a timer is inserted between them. So let us understand the working of this particular solution. So here at t0 instant switch changed from 0 to 1 it will turn the motor on immediately. At the same time timer also starts with Pt is equal to 10 seconds. So at t1 you will see that Q will reset as Et becomes Pt. So at t1 instant you will see that motor stopped running. So this is the solution for this particular example. These are the references you can refer for the further reading. Thank you.