In electrical intrinsic safety explosion-proof, we generally divide the workplace into explosion-proof areas and non-explosion-proof areas. There is the 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 current 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 electric sparks.
According to the different structures, safety barriers are divided into two types: Zener safety barrier and Isolated safety barrier.
The Zener safety barrier is connected in series with a fast fuse, a current-limiting resistor and a parallel voltage-limiting Zener diode in its internal circuit, and then completes the effect of confinement energy, which has the following characteristics:
(1) There must be an independent and very reliable grounding system (intrinsically safe system grounding), and the grounding resistance should be less than 1Ω;
(2) Electrical signal conversion cannot be carried out, and signals such as thermocouples/RTDs may be faulted due to electromagnetic disturbances, so they are not suitable for connection with this type of sensor;
(3) The power supply voltage has a great impact, 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 the fast fuse will be blown out and damaged when it is severe. According to the regulations, the internal Zener tube, current limiting resistor, and fuse are poured as a whole, and they cannot be repaired once damaged;
(4) Small size, cheap price, no rated power supply;
The input, output and power supply of the barrier safety barrier are blocked from each other, and it has the following characteristics:
(1) There is no need for grounding wire, and the 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 thermocouples/RTDs/frequencies, such as converting them into 4-20mA current signal output, and has strong anti-disturbance ability;
(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 requires external power supply;
Although barrier barriers are relatively expensive, their excellent functionality and ease of construction make them widely used in industrial sites. Next, let's introduce a barrier safety barrier product from P+F.
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