PLC Programming what is ladder?
Ladder is the instruction set used in plc programming. This tutorial series will go through all the instruction sets which we use in programming plcs with Ladder. If you don’t know what plcs are here is a great article on the plc meaning. Ladders accommodates for circuit simulation in the plc. Which allows us to control devices with the plc using the ladder language.
What software will we use to program our plc?
We will be using the free version of RSLogix 500 / RSLogix Micro to compile our Ladder logic in. Also this piece of software has most of the instructions you will need to get to know to start programming plcs. When opening the interface you should have something like this in your view.
In this example you will see two distinct lines. These lines are called rungs and generally run in a threaded fashion. These can often be thought of as conditions in your ladder logic and can be compared to if statements in modern programming languages.
Basics of input and output instructions
Let’s now start talking about input and output instructions. In general input is used to gather information for our plc from it’s surroundings as well as use that information to execute ladder instructions. Output is the output given to devices attached to our plc which controls their behavior. There are two main branches of IO in plcs. Digital/Discrete and Analog IO. Digital IO are usually in binary terms, on/off, zero or one, true or false. In the general terms of PLC we refer to these states as energize and de-engergize. Analog on the other hand can provide information in terms of ranges as a result this gives you more flexibility. For example 12V – 24V. Thus you will use analog signals in situations where there is a measurement in a range of some sort.
In our next plc programming tutorial we will deal with some actual instructions and show how to set them up in RSLogix so that ou can run them yourself.
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