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What are Flameproof and Intrinsically Safe Instruments

In the instrument industry, I came into contact with the term explosion-proof level, so I learned about explosion-proof instruments and intrinsically-safe instruments. The focus of this article is to introduce the characteristics of explosion-proof instruments and intrinsically-safe instruments.

What is a flameproof instrument

Explosion-proof, also known as pressure-proof explosion-proof, encloses the instrument components that can ignite the explosive mixture in a shell, which is particularly strong, can withstand the explosive pressure of the explosive mixture inside, and prevent the explosive mixture from transmitting to the outside of the shell. That is to say, the explosion-proof instrument housing may explode inside, but it will not be transmitted to the outside of the housing. Therefore, the joint surfaces of various parts of this instrument, such as the number of thread turns of the instrument cover, and the thread accuracy, The zero point, the gap between the range adjustment screw and the case, the gap between the detection part and the conversion part of the transmitter, and the wire port have strict explosion-proof requirements.

Except for explosion-proof instruments, which are relatively bulky, they are relatively simple and do not require related equipment such as safety barriers. However, before opening the cover, the power must be turned off, otherwise, if a spark is generated, it will be exposed to the atmosphere, causing danger.

What is an intrinsically safe instrument

Intrinsically safe instruments are also called safety spark instruments. Its characteristic is that under normal and fault conditions, the sparks generated by circuits and systems and the temperature reached will not ignite explosive mixtures. Its explosion protection is mainly achieved by the following measures:

① The instrument circuit is composed of new integrated circuit components, etc., and works at lower operating voltage and lower operating current;

② Use safety barriers to separate the electrical circuits in hazardous and non-hazardous locations, and limit the energy transferred from non-hazardous locations to hazardous locations;

③ The connecting wires of the meter must not form excessively distributed inductance and capacitance to reduce the energy storage in the circuit.

The explosion-proof performance of the safety instrument of this system is not achieved by external measures such as ventilation, inflation, oil filling, and flameproof, but by the circuit itself, so it is intrinsically safe. It can be applied to all hazardous locations and all explosive gas and vapor mixtures, and can be repaired and adjusted under power. However, it cannot be used alone. It must be used with intrinsically-safety-related equipment (safety barrier) and external wiring to form an intrinsically safe circuit in order to play an explosion-proof function.

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