Understanding the functions, features, principles, classification and selection of signal isolators (I)

The function of the signal isolator is simply to isolate, filter, amplify, convert and distribute the input signal to other instruments or systems to improve the signal's immunity to electromagnetic interference. This paper briefly introduces the functions, features, principles and classification of signal isolators.

Signal isolation transmitter function:

The signal isolation transmitter mainly modulates and transforms the input signal through the internal semiconductor device, and isolates and transmits the signal through the photoelectric coupling device or the digital isolation device, and then demodulates and converts into the original signal before isolation. The main functions are as follows:

1.Isolation

Industrial field instruments, actuators and other equipment are basically grounded. The potential difference between the devices will cause the ground loop to appear, which will cause the signal transmission process to be disturbed. In addition, once a strong voltage surge occurs in the control loop, none of the associated equipment in the loop will be spared. The signal isolator generally adopts three-terminal isolation technology, and each process link is effectively isolated to ensure the signal transmission accuracy and completely solve the problems of ground loop current and signal isolation protection.

2.Filtering

Inverter and motor equipment are widely used in industrial sites. The coupling interference caused by strong electromagnetic radiation often causes “glitch” in signal distortion. Some signals can not effectively solve this problem by using shielded cables. For some important analog signals, the use of isolators ensures the stability and reliability of data transmission.

3.Zoom

During the long-distance transmission of analog signals, an isolator is added to amplify the signal, which can effectively improve the signal load capacity and ensure the accuracy and reliability of the transmitted signal.

4.Conversion

The signal isolator can convert various types of analog signals such as voltage, current, thermal resistance, thermocouple, frequency, potential and other signals into standard signals, and isolate the signals while solving the signal matching problem.

5.Signal distribution and power supply for two-wire, three-wire transmitters

For the 4-20mA input isolator, Changhui isolator is compatible with the signal isolator and distributor function. One instrument can realize the functions used, and the user does not need to configure independently. Only the different terminals can realize the required functions. When the isolator is used for signal distribution, there are several types: one input, one output, one input, two output, one input, four output, one input, four output, and one input and five output.