Every program you are using for programming has a lot of instructions you need to follow. Of course, most of them you won’t be using, but it is a good thing to know the majority. Software for programmable logic controllers is different than others, but it isn’t harder to use.
There is a couple of software you can use for PLCs, and all of them are similar to each other, so if you learn one you will manage the other easily. A lot of online courses promise that they can teach you everything you need to know, but 90% of them work on the same principle. You can learn by yourself, and just get some advices, or classes for the things that more experienced people know.
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If you look at ADD, SUB, MUL, and DIV instruction blocks, you will notice that each of them have three inputs: Source, Source B, and destination fields. The Source and Source B fields can be populated with an input rack location, a file address, an instruction field, or a fixed value. The destination field for these instructions can be populated with an output rack location, a file address, or an instruction field.
When you use them in a program, depending on which you place first you will see that input data will be shown at the first function. The program takes that data and calculates with the function you are using. If the first rung or input is closed the data will be stored in binary format.
These functions are most used for projects because of their simplicity. They can be combined because it is same as mathematical issue, if you need the data to first be multiple and then added, you use MUL than ADD function. This will also allow you to make complex calculations. Read more on this page.
Timer on delay
For every instruction you need to work on, you need to start a new project or open the existing one. Some instructions also depend on which controller you are going to use. For this example, we are going to look at RSLogix 1100. When you are online, it will automatically download the preloaded instruction sets and everything that is associated with that controller. Since this controller is a fixed controller, it is not modular, all the I/O comes in one little box, so you don’t have to add anything.
Under the main menu there are going to be instructions and underneath them are tabs with different instructions you can use. One of the tabs will be Timer or Counter. One thing you can never do is to write any logic on the end rung. So, the first thing you should do is to add rung which is the first instruction in the row.
Setting the timer
There are different timers you can use like a timer on delay and timer off delay. So, when you click on the timer on delay, you will see that it is set at the end of the instruction like an output. In front, you can put an instruction on when you want it to time and when you don’t want it to time.
You are going to address one of your push buttons, and you are going to do that by setting the “Examine if Closed” in the user tab. When it is in position, that normally open push button will not allow logic to go through. In order for logic to go through you have to push the push-button. You need to address that instruction.
You always have to give a timer a name. A timer with micro logix 500 for these controllers, the memory storage location for timers is always T4. The next step is to set the type of time base. Usually, it counts in second, but it depends on the machine and what it is processing.
A retentive timer is different than TON and TOF, and the fact that the timing accumulated value is retained. With the other two timers, as soon as you the logic in front of it, that cause at the time accumulated value to go back to zero. But, with these ones they actually retain that value.
In order to make this logic, you need to start with a rung. You will pick the timer or RTO from timer and counter tab in the functions. Also, you need to add a push button in order to start its timing. Next, you want to use an instruction of that timer that is placed under the button, and at the end also the light that will turn on after the timing.
Next step is to download the program you’ve made into the controller, and then go online. When you now push the button it will start counting which you will see in the program. While the timer is timing, usually, the green light will be on, and when it is done timing the red light will be on, the green light will shut off, and nothing else will happen until you reset that timer.
A data compare commands are input instruction that allows much more programming possibilities. Data compare instructions compare data that is stored in two or more sources and makes a decisions based on the programming instruction. Numeric data comparison that can be done are less than, equal to, less than or equal to, greater than or equal to, and not equal to.
If the equal to instruction or EQU is true the output turns on and when the Source A is equal to Source B the output turns on. Every instruction needs to follow what is going on in the input, so the output can be turned on.
To use software for programmable logic controllers you need to know basic functions you will operate with. Using rungs, calculating, and using timers is something that is changing constantly as the operation becomes more complex and machine needs to adapt to company needs.