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!
The Machine Simulator (MS) is part of the EasyPLC software suite. It has many built-in machines that can be programmed. The chain conveyor is one of these machines. It will transfer large and small boxes on the line to different locations. The productivity series of PLCs will be used to program this virtual machine.
Using the Productivity Suite software, we will connect the simulator to the chain conveyor transfer machine. This will be done using Modbus TCP (Ethernet) for communications. Using the five steps for program development we will show how this is programmed. Let’s get started. Keep on Reading!
The Click PLC retentive data memory registers are not included in the program file by default. All Click PLC CPUs are included. This option must be selected to include the C, CT, DS, DD, DH, DF, CTD, and TXT memory in the Click project file.
We will be enabling the option to include the retentive data memory in the Click program file from the Click programming software. We will also be installing a battery and programming an expiry date. This will indicate when the battery will need to be replaced. Let’s get started. Keep on Reading!
EasyPLC Software Suite is a complete PLC, HMI, and Machine Simulator Software package. This PLC learning package includes a Machine Simulator (MS). This virtual 3D world with real-time graphics and physical properties can communicate to several different programmable logic controllers. (PLC)
We will be developing a Click PLC program for a transfer line. This is just one of the prebuilt machines in the simulator to learn PLC programming. We will be developing the ladder logic, connecting via Modbus RTU, and testing our program. This will be done using the five steps to PLC program development. 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.