In addition to the role of limiting voltage and current, the isolated safety gate also has the function of current isolation. Isolation grid is usually composed of circuit limiting unit, current isolating unit and signal processing unit three parts, the basic functional circuit is shown in Figure 2. The circuit energy limiting unit is the core part of the safety gate. In addition, there are auxiliary loop supply circuits for driving field instruments and detection circuits for instrument signal acquisition. The signal processing unit performs signal processing according to the functional requirements of the safety gate.

Industrial sites generally need to use two-wire transmission mode of the distributor, not only to provide 24V distribution power for primary instruments such as pressure transmitters, but also to collect the input current signal, amplification, operation, and anti-interference processing, and then output isolated current and voltage signals for the use of secondary instruments or other instruments behind. However, some special industrial sites not only need two-wire transmission, both to provide distribution power and signal isolation function, but also need to have a safe spark explosion-proof performance, reliably prevent the mixed contact between the power supply high voltage and the signal, the use of current and voltage dual limiting loop, Safety grid is a distributor with special function that limits the energy entering a dangerous place below the safety quota.

Isolated safety gate, there are basically two types of detection end safety gate and operating end safety gate. The safety grid at the detection end is used together with the two-wire transmitter. The operating end safety gate is used with an electrical converter or electrical valve. There are also isolated safety grids of signal input and other types.

Because the isolated safety grid adopts measures such as voltage limiting, current limiting and isolation, it can not only prevent dangerous energy from entering the dangerous scene from the intrinsic safety terminal, improve the intrinsic safety and explosion-proof performance of the system, but also increase the anti-interference ability of the system, and greatly improve the reliability of the system operation.