Home > Knowledge > Content

Explosion-proof knowledge of the instrument 1

Jan 18, 2019

Explosion-proof knowledge of the instrument 1

This article comprehensively introduces the knowledge of instrument explosion protection. We often refer to explosion-proof pressure transmitters , and our instruments are often used in explosive hazardous locations, so it is especially important to understand the explosion-proof knowledge of instruments.

1. How is China's explosive hazardous areas divided?

Answer China's classification of explosive hazardous areas is equivalent to the IEC. The national standard GB 50058-92 stipulates that explosive gas dangerous places are divided into three levels according to the degree of danger, such as zone 0, zone 1, and zone 2. The explosive dust hazardous sites are divided into two zones: zone 0 and zone 11, see Table 4-1.

Table 4-1 China's Table of Classification of Hazardous Locations

Explosive substances, regional division, regional definition

Gas Zone 0 The environment in which continuous or long-term explosive gas mixtures occur

Zone 1 Environment in which explosive gas mixtures may occur during normal operation

Zone 2 An environment in which an explosive gas mixture is unlikely to occur during normal operation, or an environment where only a short-lived explosive gas mixture is present.

Dust 10 area Continuous or long-term explosive dust environment

Zone 11 An environment where the accumulated dust is sometimes raised and an explosive dust mixture occurs by chance.

Explosion-proof knowledge of the instrument

2. How is the international classification of explosive and dangerous places?

Answer The division of explosive hazardous areas by major industrial countries in the world can basically be divided into two opinions.

One is represented by IEC (International Electrotechnical Commission), including Germany, Britain, Italy, Japan, Australia and other countries. The gas is divided into 0 zones, 1 zone and 2 zones, and the dust is divided into 10 zones and 11 zones. Its definition is basically the same as the IEC (see the definition of each region in China, and the equivalent of the IEC standard in China).

The other is the division of North America countries such as the United States and Canada. It is represented by the definition of NEC (National Electrical Code). The gas is divided into Zone 1, Zone 2 (no Zone 0), and the dust is also divided into Zone 1, 2 Area.

The correspondence between the two is roughly as follows:

Gas: IEC0 area, 1 area - NEC 1 area

IEC 2 District - NEC2 District

Dust: IEC 10 District - NEC 1 District

IEC 11 District - NEC 2 District

The English of the IEC "Zone" is Zone;

The English language of NEC "District" is Division.

3. There are several types of explosion-proof electrical equipment in China's explosion-proof electrical equipment. List their names and logos.

Answer According to the national standard GB 3836-83, there are 8 types of explosion-proof electrical structures in China's explosion-proof electrical equipment, as listed below.

Structural form mark structure form mark

Flameproof d oil-filled o

Increased safety type e sand filling type q

Intrinsically safe i non-sparking type n

Positive pressure type p special type s

4. What is an explosion-proof instrument? What are the characteristics?

A Flameproof, also known as pressure and explosion proof, encloses the instrument components that ignite the explosive mixture in an enclosure that is particularly strong enough to withstand the explosive pressure of the internal explosive mixture and prevent the explosion of explosive mixtures outside the casing. That is to say, the inside of the casing of the explosion-proof instrument may explode, but it will not be transmitted to the outside of the casing, so the joint surface of the components of the instrument, such as the number of threads of the instrument cover, the thread precision, The zero point, the range adjustment screw and the case, the gap between the detection and conversion parts of the transmitter, and the wire port have strict explosion-proof requirements.

In addition to being cumbersome, the explosion-proof instrument is relatively simple, and does not require associated equipment such as a safety barrier. However, before opening the cover, the power must be turned off. Otherwise, if a spark is generated, it will be exposed to the atmosphere and danger.

Explosion-proof knowledge of the instrument

5. What is an intrinsic safety instrument? What are the characteristics?

A Intrinsically safe instrument is also called a safety spark meter. It is characterized by the fact that the instrument, the spark generated by the system and the temperature reached do not ignite the explosive mixture under normal conditions and fault conditions. Its explosion protection is mainly achieved by the following measures:

1 Using a new integrated circuit component to form a meter circuit, working at a lower operating voltage and a smaller operating current;

2 Use a safety barrier to separate the circuits in hazardous locations from non-hazardous locations and limit the energy transferred from non-hazardous locations to hazardous locations;

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

The explosion-proof performance of the safety instrument of this system is not realized by external measures such as ventilation, inflation, oil filling and explosion-proof, but is realized by the circuit itself, and thus is intrinsically safe. It can be applied to all hazardous locations and all explosive gases, vapor mixtures, and can be repaired and adjusted with power on. However, it cannot be used alone, and it must be combined with intrinsically safe equipment (safety barrier) and external wiring to form an intrinsically safe circuit.

6, Intrinsically safe type of instrument has ia, ib two, please explain the difference between them.

A ia rating—Under normal operating conditions, and when there is a fault or two faults in the circuit, the explosive gas mixture cannot be ignited. In the ia type circuit, the operating current is limited to less than 100 mA.

Ib rating—Under normal operating conditions, and when there is a fault in the circuit, the olefinic explosive gas mixture cannot be spotted. In the ib circuit, the operating current is limited to less than 150mA.

The ia type meter is suitable for zone 0 and zone 1, and the ib type gauge is only for zone 1. In other words, from the perspective of intrinsic safety, the ib type meter is suitable for underground coal mines, and the ia type meter is suitable for factories.

Explosion-proof knowledge of the instrument

7. What is a positive pressure type (p type) meter?

Answer the positive pressure of the clean air, inert gas, or continuous clean air, non-combustible gas, keep the pressure of the protective gas inside the outer casing higher than the pressure of the surrounding dangerous environment, and prevent the external explosive gas mixture from entering the shell. Instrumentation that isolates the source of electrical components from the source of danger.

You may be interested in what is a pressure transmitter.

8. What is an increased safety (e type) meter?

A metering device that does not ignite sparks or dangerous temperatures that ignite an explosive mixture under normal operating conditions and takes measures (such as sealing, etc.) to improve its safety to avoid ignition under normal and specified overload conditions. .

9. What is a special type (s type) meter?

A is a special form other than d, e, i, p, n, or a combination of the above several forms. The explosion-proof instrument adopting this structure is called a special type instrument.

10. What are the categories of explosion-proof electrical equipment?

The answer is divided into two categories: Class I: electrical equipment used in underground coal mines; Class II: electrical equipment used in factories.

11. Class II explosion-proof electrical equipment is divided into several levels? What is the logo?

Answer According to the national standard GB 3836-83, Class II explosion-proof electrical equipment is divided into three levels, the signs are A, B, C. The classification criteria are shown in Table 8-2.

Table 8-2 Classification criteria for Class II explosion-proof electrical equipment

Level MESG/mm MICR

II A 1.14>MESG≥0.9 1.0>MICR>0.8

II B 0.9>MESG>0.5 0.8≥MICR≥0.45

II C 0.5≥MESG 0.45>MICR

Note: MESG - Maximum test safety clearance for flammable gas mixtures, mm.

MICR—The ratio of the minimum ignition current of a combustible gas mixture to the minimum ignition current of methane.

II A, II B, II C are also the level of explosion of flammable gas mixtures.

Explosion-proof knowledge of the instrument

12. Explain the following nouns:

Maximum test safety clearance MESG;

Minimum ignition current MIC;

Minimum ignition current ratio MICR.

A. Maximum test safety clearance (MESG) - means that under a specified test condition, a casing is filled with a certain concentration of a mixture of test gas and air. After ignition, the casing is not ignitable through a 25 mm long joint. The maximum gap between the joint faces of the gas mixture.

Minimum Ignition Current (MIC)—The minimum current that can ignite a combustible gas mixture when subjected to 3000 ignition tests with a DC 24V, 95mH inductor spark on a specified test setup. This current is reduced by 5% and cannot be ignited.

Minimum Ignition Current Ratio (MICR) - The ratio of the minimum ignition current of a mixture of various combustible gases (or vapors) to air to the minimum ignition current of a mixture of methane and air.