In industrial automation and control systems, the concepts of upstanders and downstanders are crucial. They define the role and function of a device in a communication network. A supervisor usually refers to a device that actively sends data messages and monitors the entire system, while a subordinate is a device that passively receives data messages and provides feedback as needed. It is worth noting that PLC (Programmable Logic Controller) can be used as both the upper and lower computer due to its powerful communication capabilities and flexibility.
1. PLC as the upper computer
When PLC acts as the upper computer, it is responsible for initiating communication, sending data messages to other devices and monitoring the operation status of the whole system. In this case, PLC is usually connected with touch screen, sensors, actuators and other devices to realize the control and management of the whole system by sending commands and receiving feedback data.
For example, in the communication between touch screen and PLC, PLC is the upper computer. The touch screen sends commands to the PLC to obtain equipment status information and display it on the interface, while the PLC controls the operation of the relevant equipment according to the commands of the touch screen and feeds back the status information of the equipment to the touch screen.
2, PLC as a lower computer
However, PLC can also be used as a lower computer to communicate with other upper computer devices. In this case, the PLC is responsible for receiving commands from the host computer and executing the corresponding operations according to the commands, and at the same time feeding back device status information to the host computer.
Take the communication between PLC and inverter as an example, PLC plays the role of the lower computer here. Inverter as the upper computer, send control instructions to PLC, such as adjusting the motor speed, etc. PLC receives the instructions, through the internal program to control the working state of the inverter, and the inverter status information feedback to the inverter.
3, PLC as the upper and lower computer at the same time
In the complex control system, PLC may appear simultaneously as the upper and lower computer. For example, in the touch screen and PLC communication at the same time, another communication port of the PLC and inverter communication. In this case, the touch screen acts as the upper computer of the PLC, obtains the state information of the whole system through the PLC, and sends control commands. And PLC acts as the lower computer of the touch screen, receiving instructions and controlling the operation of related equipment. At the same time, the PLC acts as the upper computer of the inverter, sending control commands to the inverter and receiving status information of the inverter.
In this case, the PLC plays a dual role in the communication network, being responsible for receiving commands from the upper computer and controlling the operation of the devices, as well as sending commands to the lower computer and receiving its status information. This flexibility makes PLCs more widely used in industrial automation and control systems.
4, the summary
The role of PLC as an upper or lower computer depends on the specific application scenario in the communication network. Whether as an upper or lower machine, PLC provides reliable and efficient solutions for industrial automation and control systems through its powerful communication capabilities and programmability. At the same time, the existence of PLC as a dual role further extends its application scope in industrial automation and control systems.