The hottest intrinsically safe instrument related

Intrinsically safe instrument related equipment: Zener safety barrier

Zener safety barrier is generally maintained during the transfer period by the current limiting resistance that limits the output current of the intrinsically safe end and the output voltage of the intrinsically safe end: before the machinery is transferred to the construction site, it should be transferred and maintained. The operation content can be maintained according to the technical state of the machinery, and corrosion prevention can be carried out if necessary It is composed of voltage stabilizing diode (zener diode) and protective elements (fast fuse and current limiting resistor) to prevent the voltage stabilizing tube from burning. According to different protective elements, it can be divided into resistance protective safety barrier and fuse protective safety barrier. The part that can transmit stress in the material is less and less. ⑴ the principle of resistance protected safety barrier is shown in Figure 1. In a certain, the current limiting resistor R2 is used to limit the output current to meet the intrinsic safety performance requirements, and the voltage limiting elements D1 and D2 are used to limit the output voltage when the safety barrier is in normal operation. D1 and D2 are not conductive. When the safety barrier fails, such as the non intrinsically safe input terminal, and the voltage rises above the normal working voltage and reaches the conduction voltage of D1 and D2, D1 or D2 conduction limits the voltage to its stabilized voltage range. As long as D1 and D2 are not damaged, the voltage at the intrinsically safe output terminal will not rise, ensuring that it is within the stabilized voltage range of D1 or D2. R0 resistance is used to protect the voltage regulator through D1 and D2 when a large current flows through it. R1 resistance value is very small, which can be used to judge the failure of D1 or D2 when the safety barrier is in use. ⑵ the principle of fuse protective safety barrier fuse protective safety barrier is shown in Figure 2. Its circuit structure is similar to the resistance protective safety barrier, but the R0 resistance is changed to RF fuse, which makes the protection performance more safe and reliable. Figure 1 fuse protective safety barrier Figure 2 fuse protective safety barrier ⑶ Zener safety barrier structure and test requirements according to gb3836.4 standard, Zener safety barrier has the following requirements: ① when the resistance protective safety barrier adds the maximum allowable voltage at the non intrinsically safe input end, the open circuit voltage and short circuit current at the intrinsically safe output end shall not be greater than the design specified value, and at the same time, the current borne by each element The voltage or power is not greater than its rated value. ② The zener diode (zener diode) shall be placed one by one in the atmospheric air at 150 ℃ for 2h, and then cooled to room temperature. The change of its stabilized voltage value shall not exceed ± 5% or 0.5V. ③ The accuracy of the resistor shall not be less than ± 5%. ④ Fuse is an important protective element of fuse protective safety barrier, and fast fuse must be used. The fast fuse must meet the following requirements: a. the fuse has a certain overload capacity and will not fuse for 4 hours at 1.1 times the rated current. b. The fuse has the characteristic of fast fusing, and must fuse within 360s when it is 1.35 times the rated current; It must fuse within 0.5s when it is twice the rated current. ⑤ When the fuse is fused, the fuse with relevant materials shall be able to withstand the dielectric strength test of 2u+1000v (U is the maximum allowable voltage of the safety barrier). ⑥ For the voltage limiting element of fuse protective safety barrier, when the fuse is 1.1 times the rated current, the power consumption is not greater than 2/3 of its rated value; The current limiting element shall not be greater than its rated value. ⑦ The fast fusing characteristics of the fuse must also meet that under the action of the same current, the fusing time of the fuse should be less than 1/10 of the short-circuit time of the regulator tube, and the maximum current value tested should reach the quotient value of the maximum allowable voltage of the safety barrier divided by the cold resistance of the fuse. ⑧ When the fuse protective safety barrier applies voltage at the non intrinsically safe end so that the current flowing through the fuse is 1.1 times its rated current, the open circuit voltage and short-circuit current at the intrinsically safe output end shall not be greater than the design specified value. ⑨ The distance between intrinsically safe output terminal and non intrinsically safe input terminal of safety barrier shall not be less than 50mm. There shall be two grounding terminals, and the non grounded intrinsically safe circuit oil return pipe has no oil flowing out, and the terminal shall be protected by a protective cover. The circuit elements shall be arranged in sequence and sealed in the shell with resin glue. The resistance protective safety barrier can be installed in IP54, protective shell