With the development of weighing and measurement technology, weighing systems have been widely applied in industries such as petroleum, coal, chemical engineering, and pharmaceuticals
In these industries, there are numerous types of flammable and explosive gases in the hazardous chemicals operation sites (currently, there are approximately 4,000 types that have been qualitatively identified worldwide, among which over 1,900 are quantitatively identified). The production, storage, transportation and other links' process equipment are complex and changeable, and the release sources are diverse, making it difficult to analyze and determine the explosion risk factors. Therefore, a comprehensive and correct understanding of electrical explosion-proof safety technology is something we must attach importance to and take seriously.
I. Basic Components of Intrinsically Safe Systems
An intrinsically safe system is a circuit system that achieves electrical explosion-proofing by limiting electrical energy and does not restrict the usage site (where ia
It is applicable to all types of explosive gas mixtures (including all flammable gases) in Zone 0, Zone I and Zone II hazardous locations, and features high safety, maintainability and economy.
1. On-site intrinsically safe equipment
From the perspective of the energy storage components of on-site equipment, the on-site equipment in explosive gas hazardous environments should comply with intrinsically safe explosion-proof requirements
To design and take corresponding measures for the circuits containing energy storage components such as inductors and capacitors, and minimize them as much as possible,
Take into account the power consumption and temperature rise of the circuit components to ensure that no problems occur in the equipment, whether it is in normal operation or in a faulty state
Ignition caused by sparks and heat sources. That is, the on-site equipment must be intrinsically safe equipment.
The main parameters of the intrinsically safe performance of on-site intrinsically safe equipment:
Maximum input voltage (Ui): The highest voltage applied to the intrinsically safe circuit connection device without causing the intrinsically safe performance to fail
High voltage (AC peak or DC).
Maximum input current (Ii): The maximum current applied to the intrinsically safe circuit connection device without causing the intrinsically safe performance to fail
Current (AC peak or DC).
Maximum input power (Pi): When the electrical equipment is connected to an external power source without causing the intrinsic safety performance to fail, it may occur in the electrical equipment
The maximum input power of the intrinsically safe circuit consumed internally.
Maximum internal equivalent capacitance (Ci): The total equivalent internal capacitance of electrical equipment that appears through the connection device of the electrical equipment.
Maximum internal equivalent inductance (Li): The total equivalent internal inductance of the electrical equipment that appears through the electrical equipment connection device.
2. Connect the cables
From the perspective of system wiring engineering, due to the existence of distributed capacitance and distributed inductance in the connecting cables, the connecting cables become storage
Energy component. They inevitably store energy during the signal transmission process. Once an open circuit or short circuit occurs in the line, this stored energy will be released in the form of electric sparks or thermal effects, affecting the intrinsic safety performance of the system. Therefore, it is necessary to ensure that the connection transmission cables are not affected by external electromagnetic field interference and do not come into contact with other circuits, while also limiting the wiring length and the additional non-intrinsically safe energy brought by the induced electromotive force. Based on this, the allowable distributed capacitance and allowable distributed inductance of the cables are determined. The explosion-proof inspection institutions around the world mainly adopt the method of considering the distributed parameters of the cables in a centralized parameter way. The basic parameters of the intrinsic safety performance of the connection cable are as follows:
The maximum allowable distributed capacitance of the cable is Cc=Ck×L
The maximum allowable distributed inductance of the cable Lc=Lk×L
In the formula, Ck represents the distributed capacitance per unit length of the cable;
Lk- Distributed Inductance per unit length of cable;
L- Actual wiring length.
3. Associated equipment (Safety barrier
From the perspective of equipment configuration in the control room, this part of the electrical circuit must be capable of maintaining the system in a normal working state or
A protection function that can suppress the energy of intrinsically safe equipment transmitted from non-intrinsically safe circuits in safe areas to hazardous areas below the ignition limit (minimum ignition energy) in all fault conditions. The basic parameters of the intrinsic safety performance of safety barriers:
Maximum voltage (AC RMS or DC Um) : Applied to non-intrinsically safe connection devices of associated equipment without causing this
The maximum voltage at which the quality safety performance fails. Maximum output voltage (Uo): Under open-circuit conditions, the highest output voltage (AC peak or DC) that may occur in an intrinsically safe circuit when power is applied to the equipment connection device to reach the maximum voltage (including Um and Ui). Maximum output current (Io): The maximum current (AC peak or DC) from the intrinsically safe circuit of the electrical equipment connection device.
Maximum output power (Po): The maximum power of an intrinsically safe circuit that can be obtained from electrical equipment.
Maximum external capacitance (Co): It can be connected to the connection device of electrical equipment without causing the intrinsic safety performance to fail
The maximum capacitance of the quality safety circuit.
Maximum external inductance (Lo): It can be connected to the connection device of electrical equipment without causing the intrinsic safety performance to fail
The maximum inductance of the mass safety circuit.
4. Intrinsically safe system combination conditions
To ensure the safe and normal operation of the equipment, each configuration of the intrinsically safe system must meet the following conditions. ① On-site intrinsically safe equipment
The explosion-proof marking level shall not be higher than that of the safety barrier. ② The parameters of associated equipment, intrinsically safe equipment on site and connecting cables shall comply with the following inequalities.