Application of Signal Isolators in PLC/DCS Control Systems

With the continuous improvement of industrial automation, frequency converters, as power electronic devices, have been widely used in industrial control systems. However, when they undergo high-power diode rectification and transistor conversion, frequency converters often generate high-order harmonics in their input and output circuits. These high-frequency interferences can seriously disrupt power systems, loads, and nearby electrical equipment. In practical applications, especially in PLC/DCS control systems, this interference problem is particularly prominent.

Why signal isolators are needed: Interference in PLC/DCS control systems

In the industrial field, PLC/DCS control systems often encounter various issues of signal instability, one of the main reasons being the presence of electromagnetic interference. Electromagnetic interference can be divided into conducted interference and radiated interference, both of which directly affect the accuracy of measurement and control.

Types and phenomena of interference in PLC/DCS control systems

Common mode and differential mode interference

• Common mode interference mainly refers to the potential difference of the signal to the ground, usually caused by power grid intrusion, ground potential difference, and space electromagnetic radiation.

  
  

• Differential mode interference refers to interference voltage acting between the two poles of the signal, mainly caused by space electromagnetic field coupling induction and unbalanced circuit conversion.

  
  

• In the industrial field, these interferences not only cause measurement errors but also may affect the stability and safety of control systems.

Solutions to interference issues in PLC/DCS control systems

To effectively solve the interference issues in PLC/DCS control systems, the following measures can generally be taken:

• Cut off or attenuate the propagation path of electromagnetic interference.

• Improve the anti-interference ability of devices and systems, for example, by increasing the application of signal isolators.

The role of signal isolators in PLC/DCS control systems

In practical applications, signal isolators play an important role, particularly in solving signal interference problems. For example, in control systems, high-frequency interference from frequency converters often invades the control signals, causing equipment instability.

CZ2000 signal isolators

The CZ2000 series signal isolators effectively isolate and output current and voltage signals through signal acquisition, amplification, computation, and anti-interference processing, ensuring safe transmission and independence of signals. In industrial production, the CZ2000 signal isolators not only improve the load capacity of instruments but also effectively reduce interference between devices.

Application example

Take the example of a smelting technology upgrade and expansion project in a copper-nickel mine. By introducing signal isolators, the problem of high-order harmonic current interference from frequency converters to the control system was successfully solved. In this project, the use of signal isolators not only improved measurement accuracy but also greatly enhanced system stability, security, and reliability.

In summary, signal isolators in PLC/DCS control systems can effectively reduce the impact of electromagnetic interference, ensure the accuracy and safety of the control system, and have been widely applied and recognized in smelting, water treatment, chemical engineering, thermal power, and industrial automation fields.