In electrical intrinsic safety explosion-proof (abbreviation: intrinsically safe explosion-proof), we generally divide the workplace into explosion-proof area and non-explosion-proof area. There is a transmission of electrical energy between the explosion-proof area and the non-explosion-proof area, for example, the switches, buttons, sensors, etc. in the explosion-proof area are connected to the PLC placed in the electrical cabinet in the non-explosion-proof area through wires. The effect of the safety barrier is to limit the energy between the explosion-proof area and the non-explosion-proof area, which reduces the electrical energy of the signal in the explosion-proof area, and then reduces the risk of electrical sparks.
According to the different structures, safety barriers are divided into two categories: Zener safety barrier and Isolated safety barrier.
In its internal circuit, the Zener safety barrier is connected in series with fast fuses, current-limiting resistors and parallel voltage-limiting Zener diodes, and then realizes the effect of confinement energy, which has the following characteristics:
(1) There must be a separate and very reliable grounding system (intrinsically safe system grounding), and the grounding resistance should be less than 1Ω;
(2) Electrical signal conversion is not possible, and signals such as thermocouples/RTDs may be incorrect due to electromagnetic disturbances, so it is not suitable for connecting this type of sensor;
(3) It has a great impact on the power supply voltage, and the fluctuation of the power supply voltage may cause the current leakage of the Zener diode, and then cause the error of the signal or send out the wrong level, and in serious cases, the fast fuse will be blown out and permanently damaged. According to the regulations, the internal Zener tube, current limiting resistor and fuse of the Zener safety barrier are poured as a whole, and once damaged, they cannot be corrected;
(4) Small size, cheap price, no need for additional power supply;
The input, output and power supply of the barrier barrier are blocked from each other, and it has the following characteristics:
(1) There is no need for grounding wire, and on-site construction is very convenient;
(2) Because the signal line does not need to be grounded, the stability and anti-disturbance ability of the whole system are greatly enhanced;
(3) It has the ability of signal conversion, which can process signals such as thermocouple/RTD/frequency, for example, it can be converted into a current signal output of 4-20mA, and the anti-disturbance ability is relatively strong;
(4) The general barrier safety barrier has two output channels, which are electrically blocked from each other and do not affect each other;
(5) The price is relatively expensive, and external power supply is required;
Although barrier barriers are relatively expensive, their excellent performance and ease of construction make them widely used in industrial sites.
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