Programmable Logic Controller Application Overview

Open-loop control
Open-loop control of switch quantity is the most basic control function of PLC. The instruction system of PLC has powerful logical operation ability, and it is easy to realize various logical control methods such as timing, counting, sequence (stepping), etc. Most PLCs are used to replace traditional relay contactor control systems. [9]
Analog closed-loop
For analog closed-loop control systems, in addition to the input and output of switch quantity, there must also be analog input and output points to sample input and adjust output to achieve continuous adjustment and control of parameters such as temperature, flow, pressure, displacement, speed, etc. At present, not only large and medium-sized PLCs have this function, but also some small machines have this function. [9]
Digital control
When the control system has a rotary encoder and a pulse servo device (such as a stepper motor), the PLC can be used to realize the function of receiving and outputting high-speed pulses to realize digital control. More advanced PLCs have also specially developed digital control modules to realize curve interpolation functions. Recently, a new motion unit module has been launched, which can also provide a programming language for digital control technology, making it easier for PLC to realize digital control. [9]
Data acquisition and monitoring
Since PLC is mainly used for field control, collecting field data is a very necessary function. On this basis, PLC is connected to the host computer or touch screen, which can not only observe the current value of these data, but also conduct statistical analysis in a timely manner. Some PLCs have data recording units, and the memory card of a general personal computer can be inserted into the unit to save the collected data. Another feature of PLC is that it has many self-test signals. Using this feature, the PLC control system can realize self-diagnosis monitoring, reduce system failures, and improve system reliability.