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.
EasyPLC Software Suite is a complete PLC, HMI, and Machine Simulator Software package. This PLC learning package includes the following:
Easy PLC – PLC Simulation that will allow programming in Ladder, Grafcet, Logic Blocks, or Script.
HMI System – Easily create a visual human-machine interface (HMI)
Machine Simulator – A virtual 3D world with real-time graphics and physical properties. PLC programs can be tested using the EasyPLC or through other interfaces. (Modbus RTU, TCP, etc.)
Machine Simulator Lite – Designed to run on Android Devices.
Machine Simulator VR – Virtual Reality comes to life so you can test, train or practice your PLC programming.
We will be installing the software and showing you how to order your software package for machine simulation (MS). This includes activating your license. Let’s get started. Keep on Reading!
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 inputs are one component of our PLC block diagram. The output actions of the PLC will be controlled based on the inputs. We will be looking at digital and analog inputs that can be wired to the programmable logic controller.
We will be looking at wiring of a normally open (NO) push button, normally closed (NC) push button, 3 wire PNP sensor, and an analog sensor to the PLC. These will all be sinking inputs. Let’s get started. Keep on Reading!