Views: 0 Author: Site Editor Publish Time: 2023-03-08 Origin: Site
1: Intrinsically safe electronic weighing system
There are two explosion-proof types of intrinsically safe electronic weighing system: one is independent intrinsically safe explosion-proof system. All links in the system are intrinsically safe circuits, and all circuits are placed in flammable and explosive hazardous areas, that is, explosion-proof weighing sensors, explosion-proof junction boxes, intrinsically safe weighing instruments, and intrinsically safe explosion-proof power supplies are all placed in hazardous areas. The explosion-proof sign is "Exib Ⅱ BT4". The other is a hybrid intrinsically safe explosion-proof system. There are intrinsically safe circuits and non intrinsically safe circuits in the system, that is, explosion-proof load cells and explosion-proof junction boxes are placed in dangerous areas, and the safety barriers between the weighing instruments and explosion-proof junction boxes (used to isolate high and low levels) are placed in safe areas together with the weighing instruments.
When the intrinsically safe explosion-proof weighing sensor is used to assemble the intrinsically safe explosion-proof electronic weighing system, the following shall be done:
(1) : When wiring the circuit of the intrinsically safe explosion-proof electronic weighing system, it must be ensured that there will be no "mixed contact", "electrostatic induction" and "electromagnetic induction" between the wiring of the intrinsically safe associated circuit and the general circuit, so as to avoid increasing the dangerous voltage and current of the intrinsically safe circuit, which may cause an explosion accident.
(2) : The wiring of the electrical equipment and associated electrical equipment of the intrinsically safe explosion-proof electronic weighing system must be connected according to the wiring diagram specified in the design drawings and product instructions. It is not allowed to connect with other lines at will or change the wiring.
(3) : The allowable distributed inductance and capacitance of the connecting cable or wire between the electrical equipment and associated electrical equipment of the intrinsically safe electronic weighing system shall meet the specified values.
(4) : The grounding requirements of electrical equipment and associated electrical equipment of intrinsically safe explosion-proof electronic weighing system shall comply with the corresponding national standards. As for the load cell, when the insulation drops, it will generate grounding current. If the grounding is poor, it is easy to generate electric sparks, which will become the ignition source in flammable and explosive hazardous areas.
(5) In addition to the grounding of system electrical equipment and associated electrical equipment, it is worth emphasizing that the metal weldment carriers, longitudinal and transverse metal limiters and enclosures, cable protection metal tubes and other non live bare metal parts set in flammable and explosive hazardous areas should be reliably grounded in accordance with the national standard GB3836.1-2000.
2: Explosion proof junction box
When multiple ia and ib intrinsically safe or d flame-proof weighing sensors are used to assemble the electronic scale in parallel, the parallel connection box is an associated device of the intrinsically safe circuit. It is not an intrinsically safe circuit, and must be designed and manufactured into an flame-proof structure. Its explosion-proof sign is "Exd Ⅱ BT6", that is, the explosion-proof type is d flame-proof type, and the gas grade is IIB (dimethyl ether, gas, cyclopropane), The ignition temperature is T6 (100 ℃ ＞ T ≥ 85 ℃, and the maximum surface temperature is 85 ℃), which is applicable to explosion-proof equipment in flammable and explosive hazardous areas 1 and 2. The junction box should preferably be made of steel. If it is made of aluminum alloy, its magnesium content should not be more than 0.5%, and its tensile strength should not be less than 12kg/mm2. During design and manufacturing, the roughness of the flameproof surface, the minimum effective length L and clearance of the joint surface, and the minimum length L1 from the edge of the bolt through hole to the edge of the flameproof joint surface, The maximum diameter difference W and other structural parameters of shaft and shaft hole flameproof joint surface must meet the flameproof requirements specified in GB3836.2-2000 National Standard for Flameproof Electrical Equipment. The shell and box cover can withstand 1MPa static pressure without leakage and permanent deformation, and the inner surface of the shell is sprayed with epoxy enamel for arc extinguishing. The internal electrical clearance shall not be less than 4mm, and the creepage distance shall not be less than 4mm.