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.
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Working principle: After the 24VDC power supply is converted by DC-AC-DC, the output module circuit needs various voltages.
The principle of the isolated safety gate at the detection end is that the module circuit converts the current or voltage signal input through the internal safety energy limiting circuit into 0.2-1VDC, sends it into the module for collection, amplification, operation and anti-interference processing, and then modulates the output isolated current and voltage signal through the transformer for the secondary instrument or other instruments to use. The module also needs to output an isolated 18.5 to 28.5VDC voltage, which is used as the operating voltage for the two-wire transmitter through the intrinsic safety energy limiting circuit. The intrinsic safety energy limiting circuit can limit the dangerous signal of high current or high voltage from entering the dangerous scene.
The principle of the isolated safety gate is that the 4-20mA DC signal output by the regulator or operator is isolated and then output the 4-20mA DC signal, which is supplied to the electrical converter or the electrical valve positioner in the field through the intrinsic safety energy limiting circuit.
The intrinsic safety energy limiting circuit can limit the dangerous signal of high current or high voltage from entering the dangerous scene.