Application of explosion-proof circuit in electromagnetic flowmeter

For mining electrical products, explosion-proof safety is extremely important. At present, the types of explosion-proof electrical products in China are mainly flameproof and intrinsically safe. And only equipment that is intrinsically safe can be used in dangerous places. Mining intrinsically safe products must undergo intrinsic safety function inspections, among which the intrinsic safety spark test is one of the most important inspection items.

When the circuit is switched on and off, energy is released in the form of sparks. When the energy is greater than a certain critical value, it will ignite the explosive gas mixture and cause an explosion. Intrinsic safety design is to control the energy of the sparks generated by the circuit and achieve the actual safety of the circuit. The actual safety circuit must be safe in both normal operation and fault conditions, and the sparks generated are not enough to ignite the explosive gas mixture in the surrounding environment.

The excitation current of the electromagnetic flowmeter sensor is a dangerous source of electric sparks. If the electromagnetic flowmeter is to be used underground, the excitation circuit must first meet the actual safety requirements. The electrical part of the electromagnetic flowmeter sensor consists of two coils, and its electrical parameters are mainly resistance and inductance. The resistance value is 40-60Ω (two coils in series), and the inductance is 100-300mH. The inductance is the source of danger. When current flows through the inductor coil, a magnetic field will be generated inside the coil, and the magnetic field stores energy. When the circuit is disconnected, the energy stored in the coil will be released in the form of sparks. Therefore, it is necessary to absorb or discharge the stored energy of the coil to meet the actual safety requirements. Connect a current branch in parallel at both ends of the coil to discharge the magnetic field energy stored in the coil and reduce the spark energy during switching. Under normal conditions, it does not affect the circuit operation. When the circuit is disconnected, it forms a discharge circuit with the coil to clamp the voltage at the forward conduction voltage drop of the diode.