Signal isolator is a signal isolation device, transmit the inputted single-way or double-way current or voltage signal into the isolated single-way or double-way linear current or voltage signal to output, and improve the electrical isolation performance between input, output and power supply.
Safety barrier: The main function of the safety barrier is to prevent the dangerous energy entering the dangerous zone, that is limit the voltages and currents which are sent to hazardous sites. It is connected between intrinsically safe circuit and non-intrinsically safe circuit, limits the voltage or current of the intrinsically safe circuit in a safe range. Safety barrier is a general name, which is divided into zener type safety barrier and isolation type safety barrier.
- Working principle of signal isolator:
Firstly, the signal of transmitter or instrument is modulated and transformed by semiconductor device, and then isolated and transformed by optical or magnetic device, then get back to the original signal or different signal through demodulating transformation, at the same time, do isolation to the power supply of the isolating signal to ensure the absolute independence of isolated signal, power supply and ground.
- Working principle of Zener Safety barrier
Zener Safety barrier circuit uses fast fuse, current limiting resistor or voltage limiting diode to limit the inputted electrical energy, Zener Safety barrier is rarely used now.
- Isolation safe barrier
3.1 Function of signal isolator
(1) Protect the subordinate control loop
(2) Attenuate the influence of ambient noise on the test circuit.
(3) Suppress the interference of the common grounding, frequency converter, solenoid valve and unknown pulse on the equipment. At the same time, it has the function of limiting voltage and frontal current for the subordinate equipment, It is the faithful protection of transmitter, instrument, frequency converter, solenoid valve PLC/DCS input and output and communication interface. DIN series rail structure, easy to install, can effectively isolate the electric potential of input, output, power supply and the earth, can overcome the interference result from frequency converter’s noise and all kinds of high and low frequency pulsation.
3.2 Advantages of signal isolator
Adopt the circuit structure of electric isolating input, output and power supply each other, meets the requirement of limiting energy for intrinsically safe type.
(1) Due to using three-party isolation, so no need system grounding line, bring great convenience for the design and site construction. Requirements for the instruments at dangerous area are greatly reduced, and isolation type instruments are not required on site.
(2) The signal line does not need common ground, which make the stability and anti-interference ability of detection & control loop signal be enhanced greatly, thus, improve the reliability of the whole system.
(3) Isolated safety barrier has stronger inputting-signal processing capacity, can received and process signals such as thermocouple, thermal resistance, frequency, etc., it is what the zener safety barrier can’t do.
(4) Isolated safety barrier can output two way isolated signals for the two devices which use the same signal source, and to ensure that the signals of the two devices do not interfere with each other, meanwhile improve the electrical safety insulation performance between the connected equipments.
Therefore, compare with the characteristics and performance of zener type barrier, isolated type safety barrier has outstanding advantages and is more widely used, although its price is slightly higher than the Zener safety barrier, but consider from the design, construction, installation, commissioning and maintenance costs, the overall cost may be lower than Zener safety barrier. Isolated safety barrier is used as the main intrinsically safe explosion-proof instrument at engineering site with high requirements. The isolated safety barrier has gradually replaced zener safety barrier and has been widely used in the field of safety and explosion protection.
Common explosion-proof certification of safety barrier are: GBEx China explosion-proof certification, CCC China compulsory product certification, IECEx international explosion-proof certification, ATEX European explosion-proof certification.