Safety design principle of explosion-proof system of intrinsically safe explosion-proof electronic scale

With the development of weighing technology, weighing system has been widely used in petroleum, coal, chemical, pharmaceutical and other industries, There are many kinds of inflammable and explosive gases in the workplace of dangerous chemicals in these industries (there are about 4000 kinds of qualitative gases in the world, including more than 1900 kinds of quantitative gases) The process equipment of production, storage, transportation and other links is complex and changeable, and there are many kinds of release sources, so it is difficult to analyze and determine the explosion risk factors Therefore, we must pay attention to and take seriously the comprehensive and correct understanding of electrical explosion-proof safety technology [Abstract] with the rapid development of weighing and measuring technology, it has been widely used in oil, coal, chemical industry and pharmaceutical industry The awareness of people-oriented and safe production is also gradually improving How to make weighing technology serve them well, we must master the design of explosion-proof system This paper introduces the requirements and details of the design of explosion-proof weighing system The aim is to promote the development of this technology I The basic composition of the intrinsic safety system: the intrinsic safety system is a circuit system that realizes electrical explosion-proof by limiting electrical energy, and does not limit the use place (the IA level is applicable in Zone 0, zone I and zone II dangerous places) and the type of explosive gas mixture (including all combustible gases), which has a high degree of safety, maintainability and economy 1 The on-site intrinsic safety equipment is considered from the perspective of the energy storage elements of the on-site equipment, so that the on-site equipment in explosive gas dangerous environment is designed according to the requirements of intrinsic safety and explosion-proof, and the corresponding measures are taken for the circuit of the energy storage elements such as inductance and capacitance, and the power consumption and temperature rise of the circuit elements are taken into consideration when minimizing them, In order to ensure that the equipment will not produce ignition caused by spark and heat source no matter in normal operation or fault state That is, the field equipment must be intrinsic safety equipment The main parameters of the intrinsic safety performance of the on-site intrinsic safety equipment: Zui high input voltage (UI): Zui high voltage (AC peak or DC) applied to the intrinsically safe circuit connection device without invalidating the intrinsic safety performance Zui high input current (II): Zui high current (AC peak or DC) applied to the intrinsically safe circuit connection device without invalidating the intrinsically safe performance Zui high input power (PI): the Zui high input power of the intrinsically safe circuit that may be consumed inside the electrical equipment when the electrical equipment is connected to the external power supply without invalidating the intrinsic safety performance Zui large internal equivalent capacitance (CI): the total equivalent internal capacitance of electrical equipment through the connection device of electrical equipment Zui large internal equivalent inductance (LI): the total equivalent internal inductance of electrical equipment through the connection device of electrical equipment 2 From the point of view of system wiring engineering, connecting cables become energy storage elements because of distributed capacitance and distributed inductance They inevitably store energy in the process of signal transmission Once there is an open circuit or a short circuit in the circuit, these stored energy will be released in the form of electric spark or thermal effect, which will affect the intrinsic safety performance of the system Therefore, it is necessary to ensure that the connecting transmission cable will not be affected by external electromagnetic interference and mixed contact with other circuits, and limit the additional non intrinsic safety energy brought by the wiring length and induced electromotive force, so as to determine the allowable distributed capacitance and allowable distributed inductance of the cable All explosion-proof inspection organizations in the world mainly consider the cable distribution parameters in the way of centralized parameters The basic parameters of the intrinsic safety performance of the connecting cable are as follows: Cable Zui large allowable distributed capacitance CC = CK × l cable Zui large allowable distributed inductance LC = LK × l where CK -- cable unit length distributed capacitance; LK -- cable unit length distributed inductance; L -- actual wiring length 3 From the perspective of equipment configuration in the control room, the associated equipment (safety barrier) must have the protection function that the energy transferred from the non intrinsically safe circuit in the safe place to the intrinsically safe equipment in the dangerous place can be restrained below the ignition limit (Zui small ignition energy) no matter the system is in normal working state or fault state Basic parameters of intrinsic safety performance of safety barrier: Zui high voltage (AC effective value or DC UM): Zui high voltage applied to non intrinsically safe connection device of related equipment without invalidating intrinsic safety performance Zui high output voltage (UO): the Zui high output voltage (AC peak value or DC) of intrinsically safe circuit that may occur when the power applied by the equipment connecting device reaches Zui high voltage (including um and UI) Zui high output current (IO): Zui high current (AC peak or DC) from intrinsically safe circuits of electrical equipment connection devices Zui high output power (PO): the intrinsically safe circuit Zui high power that can be obtained from electrical equipment Zui large external capacitance (CO): Zui large capacitance of intrinsically safe circuit that can be connected to the connection device of electrical equipment without invalidating the intrinsic safety performance Zui large external inductance (LO): Zui large inductance of intrinsically safe circuit that can be connected to the connecting device of electrical equipment without invalidating the intrinsic safety performance 4 Combination conditions of intrinsic safety system: in order to ensure the safe and normal use of equipment, the following conditions must be met for each configuration room of intrinsic safety system ① The explosion-proof mark level of the on-site intrinsic safety equipment shall not be higher than that of the safety barrier ② the following inequality shall be met between the parameters of the associated equipment, on-site intrinsic safety equipment and the connecting cable Matching conditions for safety parameters of safety barrier parameters parameters of intrinsic safety instruments, cables and other parameters uo ≤ UI
Io
≤
Ii
Co
≥
Ci+Ce
Lo
≥
Li+Le