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Explosion-Proof Knowledge Of The Instrument 2

Jan 18, 2019


Explosion-Proof Knowledge Of The Instrument 2

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.


Explosion-Proof Knowledge Of The Instrument

13. Class II explosion-proof electrical equipment is divided into several temperature groups? What is the logo?

Answer According to the national standard GB3836—83, Class II explosion-proof electrical equipment is divided into 6 groups according to its highest surface temperature, and the marks are T1~T6. The grouping criteria are as follows:

Temperature group Allowable maximum surface temperature / °C temperature group Allowable maximum surface temperature / °C

T1T2T3 450200200 T4T5T6 13510085

T1-T6 correspond to the ignition temperature grouping of the explosive gas mixture.

14. How to choose an explosion-proof instrument?

A Generally speaking, it can be selected according to the following two points.

1 Select the explosion-proof type of the instrument according to the dangerous area where the instrument is installed and used:

Zone 0 - can only choose ia type, S type (refers to the S type designed for Zone 0);

Zone I - other types than n;

Zone 2 - all explosion-proof versions are optional;

2 Select the explosion-proof grade and the maximum allowable surface temperature group of the instrument according to the possible flammable gas, vapor emission level and ignition temperature group. See Table 8-3, which is summarized according to GB3836-1983.

Table 8-3 Examples of combustible gas, vapor explosion level, and ignition temperature group

Group level T1 (T>450°C) T2 (450°C≥T>300°C T3 (300°C≥T>200°CT4(200°C≥T<135°C T5(135°C≥T<100°C T6(100°C) ≥T<85°C)

II A methane, ethane, propane, styrene, benzene, toluene, xylene, trimethylbenzene, naphthalene, mono-carbonized carbon, phenol, cresol, acetone, methyl acetate, acetic acid, ethyl chloride, chlorobenzene, ammonia, Acetonitrile, aniline butane, cyclopentane, propylene, ethylbenzene, cumene, methanol, ethanol, propanol, butanol, methyl formate, ethyl formate, ethyl acetate, methyl methacrylate, vinyl acetate , dichloroethane, vinyl chloride, methylamine, dimethylamine pentane, ethane, heptane, octane, decane, decane, cyclohexane, turpentine, naphtha, petroleum, gasoline, fuel oil, Kerosene, diesel, pentanol, hexane, cyclohexanol, trimethylamine nitrite

II B propyne, cyclopropane, propylene wax, hydrogen cyanide, civil gas ethylene, butadiene, ethylene oxide, propylene oxide, methyl acrylate, ethyl acrylate, furfuryl ether, crotonaldehyde, propylene Aldehyde, tetrahydrofuran, hydrogen sulfide ethyl methyl ether, diethyl ether, di-ether ether, tetrafluoroethylene

II C chlorine, water gas acetylene carbon disulfide ethyl nitrate

Description: a, flammable gas, vapor explosion level is also the explosion-proof level of electrical equipment, the two are consistent, are divided into IIA, IIB, IIC three.

b. The ignition temperature range of flammable gases and vapors corresponds to the highest surface temperature group of electrical equipment. For example, the gas of T4 group has an ignition temperature of 200 °C≥T>135°C.

Explosion-Proof Knowledge Of The Instrument

15. What parts of China's explosion-proof signs are made up of? Explain their meaning separately?

Answer The explosion-proof mark generally consists of the following five parts:

1 explosion-proof mark EX—indicating that the device is an explosion-proof electrical device;

2 Explosion-proof structure form - indicating what measures the equipment uses for explosion-proof, such as d is explosion-proof type, p is positive pressure type; i is intrinsic safety type;

3 explosion-proof equipment categories - divided into two categories, I is underground coal mine electrical equipment, II is factory electrical equipment;

4 Explosion-proof level - divided into three levels A, B, C, indicating the strength of its explosion-proof capability;

5 Temperature group - divided into six groups of T1 ~ T6, indicating the maximum surface temperature allowable value of the device.

16. The explosion-proof mark of one instrument is EXdIIBT4, please explain its meaning.

Answer EX - the general mark of explosion protection;

D——structural form, explosion-proof type;

II - category, factory use;

B——Explosion-proof level, Class B

T4 - temperature group, T4 group, the highest surface temperature ≤ 135 °C.

17. The explosion-proof mark of a polyester power junction box is EXedIICT4, please explain its meaning.

Answer EX - the general mark of explosion protection;

Ed - structural form, e: increased safety type, d: flameproof type;

II - category, factory use;

C——explosion-proof grade, grade C

T4 - temperature group, T4 group, the highest surface temperature ≤ 135 °C.

18. The explosion-proof mark of an imported gas chromatograph is EEXdpsIIB+H2T4, please state its meaning.

Answer EEX - the European Community's general mark of explosion protection;

Dps - the instrument uses explosion-proof, positive pressure, special three kinds of explosion-proof measures;

II - electrical equipment for the factory;

B——Explosion-proof level, Class B

+ H2 - also suitable for H2 (B-class explosion-proof is not applicable to H2, the instrument can also be used in H2 places due to various explosion-proof measures);

T4 - the highest temperature rise of the surface ≤ 135 ° C.

19. The explosion-proof mark of a Japanese-made instrument is JISia3Ng4. Please explain its meaning.

Answer JIS - Japanese Industrial Standard Code;

Ia - intrinsically safe explosion-proof, ia grade;

3n - explosion-proof grade is 3n, against all grade 3 explosive gases, equivalent to China's IIC;

G4 - temperature group, equivalent to China's T4.

Description JISia3nG4 is an explosion-proof mark used in Japan. Now Japan has adopted the IEC standard. The above-mentioned explosion-proof mark is now marked as JISEXiaIICT4.

Explosion-Proof Knowledge Of The Instrument

20. The explosion-proof marks of an imported instrument are Class1, Division1, GroupB, C, D, T4A, please explain its meaning.

Answer Class 1-1, a flammable gas or vapor site;

Division 1-1, where there is or may be a site of explosion or burning;

GroupB, C, D—suitable for locations where hazardous gases are present in Groups B, C, and D;

T4A—The highest surface temperature is ≤120°C.

The above-mentioned explosion-proof mark corresponds to China's EXIIA, IIB, IICT4, and can be used in hazardous areas in Zone 0 and Zone 1. However, it should be noted that this watch cannot be used in acetylene sites.

21. The explosion-proof mark of an imported instrument is as follows, please explain its meaning.

UL/FM/CSA Class1, GroupB, C, D, T5

Class3, GroupE, F, T5

CENELEC EEXedIICT5

Answer UL - American Insurance High Laboratory;

FM - United States Factory Joint Research Association;

CSA - Canadian Standards Association;

CENELEC - European Electrotechnical Commission.

It shows that the explosion-proof performance of the instrument has been approved by UL, FM, CSA and CENELEC tests.

Class1, GroupB, C, D, T5—Applicable to the combustible gas of Group B, C, and D specified by NEC, with surface temperature ≤100°C.

Class2, GroupE, F, and T5 are applicable to the E and F dusts specified by NEC, and the surface temperature is ≤100 °C.

EEXedIICT5—in accordance with EN standards (EN is the European Community standard code, its explosion-proof standard is equivalent to IEC), factory explosion-proof instrument, increased safety, explosion-proof type, explosion-proof grade C, the highest surface temperature ≤100 °C.

22. Is there any limit to the transmission distance of the transmitter output signal?

A The current production of capacitive transmitters, the power supply is 24VDC, according to the instrument's maximum output of 22.5mA, the minimum operating voltage of 10.5VDV, its load resistance is 600Ω. For the explosion-proof transmitter, as long as the sum of the resistance of the wire harness and the device of the transmitter does not exceed 600 Ω, the transmission distance of the wire is not limited. However, for intrinsically safe transmitters, the length of the wire is specified. Because intrinsic safety is a system, not only an intrinsically safe instrument, but also related equipment and external wiring. Associated devices are generally safety barriers, which are required for the length of the conductors, each with a maximum allowable inductance and a maximum allowable capacitance. If the distributed capacitance and inductance of the wire plus the unprotected capacitance and inductance of the transmitter exceed the specified range, the instrumentation system is unsafe.

23. What are the requirements for installing the instrument in an explosion-hazardous location?

A1 Instruments, electrical equipment and installation materials used in explosion hazardous areas, such as junction boxes, junction boxes, terminal boxes, etc., must have an explosion-proof certificate issued by a national authorized agency. Before installation, check whether the specifications and models meet the design requirements. There should be no damage or crack on the outside.

2 In the explosion hazardous area, the instrument box with positive pressure explosion-proof can also be installed, and the non-explosion-proof type meter and other electrical equipment should be installed. The air tube of the instrument box must be kept open. Before the power transmission, the gas should be more than 5 times the volume of the box. Replacement.

3 Instrument wiring in Zone 1 of the explosion hazardous area must ensure that the ignition source is not formed in case of grounding, short circuit or disconnection. Therefore, cables and wires must be laid through pipes. Pressure-proof and explosion-proof metal pipes, between the thread-protecting pipes and between the protective pipes and the junction box, the distribution box, and the cable box should be connected by a cylindrical pipe thread. Should be above 5~6 buckles. Explosion-proof flexible connecting pipes are required for flexible connections.

Instrument wiring in Zone 2 should generally be piped, but only to protect the insulation of cables and wires from trauma.

4 When the junction trough, cable trench and protective pipe pass through the boundary of different levels of explosion hazard sites, sealing measures shall be taken to prevent explosive gas from entering a dangerous place from another dangerous place.

5 When the protection pipe is connected with the field instrument, detection component, electrical equipment, instrument box, distribution box, junction box, cable box, etc., the explosion-proof sealing pipe fitting should be installed within 0.45m of the connection, and the protection pipe for 2in or more A sealed pipe fitting should be provided for 15m.

24. What are the requirements when installing intrinsically safe instruments?

Answer 1 Different series of intrinsically safe instruments and safety barriers and other related equipment should not be mixed casually. It must be verified by relevant departments to confirm that their technical performance is compatible and then replace each other.

2 Intrinsically safe related equipment such as safety barriers, galvanic isolators, buffer amplifiers, etc., should be installed on the side of the safe place and reliably grounded.

3 In order to prevent the wiring of the intrinsically safe system from causing dangers due to mixing, static induction and electromagnetic induction between the intrinsically safe related circuit and the wiring of the general circuit, pipe laying should be adopted. The intrinsically safe and non-intrinsically safe lines should not share a single cable or protective tube. Intrinsically safe circuits of two or more different systems shall not share a single cable (except for those shielded by core wires) or share the same protective pipe (except for shielded wires).

4 When the intrinsically safe and non-intrinsically safe lines are laid in the same sink and cable trench, the grounded metal plates or insulation should be used for isolation. Otherwise, they should be arranged separately, the spacing is greater than 50mm, and they are fixed separately.

5 The terminal boards of the intrinsically safe and non-intrinsically safe lines in the instrument panel should be separated from each other with a spacing greater than 50mm. Otherwise, the insulation board should be used for isolation. The two types of lines should be laid separately and the binding should be firm.

6 The length of the intrinsically safe line shall be such that its distributed capacitance and distributed inductance do not exceed the maximum allowable value specified by the instrument manufacturer.

7 The wiring of the intrinsically safe system should generally be set with a blue mark.

8 The intrinsically safe line should not be grounded, but it should be grounded when the signal grounding reference point needs to be set. This grounding point should be a single grounding point of all intrinsically safe instrument system grounding conductors and separate from the power grounding system.