Developing a programmable logic controller (PLC) program can be broken down into five different steps. These programming steps are as follows:
Five Steps to PLC Program Development
Step 1 – Define the task
Step 2 – Define the Inputs and Outputs
Step 3 – Develop a logical sequence of operation
Step 4 – Develop the PLC program
Step 5 – Test the program
These five steps to PLC program development will help you in understanding, programming, and troubleshooting your automated machine.
We will be looking at each of these steps in a little more detail as we discuss the PLC programming development. Let’s get started. Keep on Reading!
Programmable logic controllers (PLC) use a cyclic scan. The time that it takes to complete one scan is called Scan Time. Typical scan times range from 10 milliseconds to 10 microseconds. This translates from 0.01 to 0.0001 seconds per PLC scan. Understanding how the program scan will help us in programming and troubleshooting the PLC.
The simplest scan cycle of a PLC consists of 4 steps. Read inputs, execute program, diagnostics, and communication, and update outputs.
We will be looking at each of these steps in a little more detail as we discuss the PLC program cyclic scan. Let’s get started. Keep on Reading!
All programmable logic controllers (PLC) have the same numbering system at their core. This is the same with all computers as well. The status of any memory location can be either on or off. A one (1) will represent an on or “True” status and zero (0) will represent an off or “False” status. This is called binary.
PLC memory is very similar to personal computer memory. There is the operating system and firmware of the processor and connected modules. PLC programs and data that are used by the program are also stored in the memory.
We will now look at the basic understanding of memory in the PLC. Looking at two examples of PLC specifications. We will see how the program is stored and how long data memory will remain when the PLC is not powered up. Let’s get started. Keep on Reading!
PLC outputs are the next component of our PLC block diagram. The outputs of the PLC will be controlled by the PLC program. Controlling outputs is one way to get the inputs to change. We will be looking at digital and analog outputs that can be wired to the programmable logic controller.
PLC troubleshooting outputs will also be discussed. This will be done using a multimeter measuring voltage both at the PLC output and across the discrete output load. We will also measure and control an analog signal output. Let’s get started. Keep on Reading!