PLC Pulse Signal Timer .01S, .1S, 1S, & 60S Clock pulse- In this tutorial, you will learn how to use the PLC Special Relays for generating clock pulses instead of using the regular PLC Timers. My last article was based on the PLC Timers and Counters. For the basic understanding, I highly recommend, first read my previous article and then you can resume from here. In the Title image, you can see M1920, M1921, M1922, and M1923. These are basically the PLC special relays used as the PLC Pulse Generator. So this article is all about these Special Relays, we will discuss each one in detail and I will practically use these Special Relays so that you can better understand.
Without any further delay let’s get started!!!
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As you know in Fatek PLC there are a total of 256 Timers (T0 ~ T255) which I have already explained in my previous article.
T0 ~ T49: 0.01S timer (default as 0.00 ~ 327.67S)
T50 ~ T199: 0.1S timer (default as 0.0 ~ 3276.7S)
T200~T255: 1S timer (default as 0 ~ 32767S)
Let’s make a 1 second pulse generator using the T200 timer to best explain the difference.
PLC pulse generator 1 Second:
Using a regular timer generating a 1-second pulse looks really complex. The output y0 remains OFF for one second and then remain ON for 1 second. This cycle is repeated again and again until the switch connected with the X0 input is turned OFF.
But the same thing can be done quite easily using the 1 second Special Relay clock pulse which is M1922.
This is also a 1-second pulse generator. Now you can see the difference in how easy it is. Let’s discuss these Special Relay clock pulses.
PLC Special Relays “Pulse Signals”:
Following are the Pulse Signals
M1920 .01S Clock pulse
M1921 .1S Clock pulse
M1922 1S Clock pulse
M1923 60S Clock pulse
M1924 Initial pulse (first scan)
M1925 Scan clock pulses
We will only discuss M1920, M1921, M1922, and M1923.
M1920 Clock Pulse PLC Ladder Logic Diagram:
M1921 Clock Pulse PLC Ladder Logic Diagram:
M1922 Clock Pulse PLC Ladder Logic Diagram:
M1923 Clock Pulse PLC Ladder Logic Diagram:
Let’s make the seconds counter using the 1S clock pulse M1922.
The purpose of the above Ladder Logic Diagram is to count the seconds using the counter function. The switch connected with the X0 input of the Fatek PLC is used to clear the counter. The Preset value is 5. When the counter counts 5 seconds the load connected with the Y0 output of the PLC is turned ON. The same thing can be done for all the other clock pulses. Now let’s make an advanced level seconds counter system.
Advanced Seconds counter Example:
In this example, we are going to attempt something very cool which you can use in advanced level projects. Let’s say you are told to count the seconds and store the value at a certain memory location and perform the comparison, whether the seconds are less than, equal to, or greater than a Predefined value and control a certain load depending on the result of the comparison. Let’s do it.
This job can’t be done using simple counters (C0 ~ C255). But we can also count pulses using the increment function. The best thing about the increment function is that you can specify a location in the memory.
For this particular example, we will need two memory locations. One location for storing the number of seconds counted and the other memory location for the Preset/Predefined value. For this, you will have to make a register table which is very easy.
As you can see there is a Register Table, right-click on this and then click on the Add Register Table.
Enter the Table name, specify the Table Starting Address, select the fixed length and enter the number of data register you want.
The predefined value of 5 is stored in the D1 while the seconds will be stored in the D0.
The time you add the increment function set the D0 as the destination address, while in the comparison select D0 and D1. D0 and D1 will be compared and the outputs Y0, Y1, and Y2 will be controlled accordingly.
Now using the same concept you can make the vehicles speed monitoring system. You can use two sensors at two different locations. One sensor activates the M1922 and the other sensor stops the M1922. The time taken by the vehicle from sensor1 to sensor2 can be stored in a particular register and then using the arithmetic function the speed can be calculated. This is your homework. Leave a comment if you have done it.