Installing signal isolators on PLC control cabinets

In the field of industrial automation, PLC (Programmable Logic Controller) control cabinets play a crucial role, responsible for receiving signals from various sensors and actuators, and achieving precise control of the production process through internal logic operations. However, in practical applications, PLC control cabinets often face various complex electromagnetic environments and signal interference problems, which may lead to control system malfunctions, frequent failures, and even pose a threat to equipment and personnel safety. Therefore, adding signal isolators to PLC control cabinets has become a common solution.

The main functions of signal isolators include preventing the transmission of electromagnetic interference, reducing the occurrence of system failures, and providing isolation in the event of equipment failures on site, preventing the spread of faults to the entire control system. By modulating and transforming the signals received by the PLC through semiconductor devices, then isolating and converting them using optical or magnetic sensing devices, and finally demodulating and transforming them back to the original signal or different signals, this process ensures the stability and accuracy of the signal, while also preventing damage to the PLC and reducing the impact of on-site signals on the PLC, especially clutter signals. In addition, signal isolators can also achieve signal conversion, such as converting signals from PT10 connections into 4-20mA signals and inputting them into PLC systems, effectively avoiding conflicts between electricity and power sources and solving the problem of mutual interference between loops and equipment.

In specific applications, such as in the production line of a steel plant, measurement and control are achieved through PLC, on-site automation instruments, and on-site actuators. The PLC is placed in a control cabinet located several hundred meters away from the site (working at room temperature), and automation instruments or thermocouples from the site output signals through wires into the control cabinet in the control room. At this point, the signal entering the PLC must be isolated and may also need to be converted, such as isolating 4-20mA and converting it to 0-5V before entering the PLC. The equipment that completes the isolation and conversion of thermocouple signals is called a "thermocouple signal isolator" or "thermocouple temperature transmitter". Its core function includes isolating the input signal and output signal, as well as converting the input mV level signal from the thermocouple into standard industrial signals (4-20mA, 0-5V, 0-10V).

In summary, installing signal isolators is of great significance for improving the reliability of industrial automation systems, reducing failure rates, protecting PLC equipment, and improving signal quality. It is one of the important components to ensure the stable and reliable operation of control systems