1、 Overview

Explosion proof thermocouple is made according to Q/ZZ HHX002-2012 "HX-WR Explosion proof Thermocouple", GB3836.1-2010 "Explosive Environment Part 1: General Requirements for Equipment", and GB3836.2-2010 "Explosive Environment Part 2: Equipment Protected by Explosion proof Shell". Its explosion-proof mark is Ex d Ⅱ C T6 Gb.

This product is a measuring sensor device used in factory environments with explosive gases, steam, and mist. It is usually used in conjunction with display instruments, regulating instruments, transmitters, etc. to directly measure the temperature of various gases and liquid media in various production projects.

This product has passed the inspection of the National Explosion proof Electrical Product Quality Inspection Center and obtained an explosion-proof certificate, with the explosion-proof certificate number CNEx13.

2、 Principle

1. Temperature measurement principle

The working principle of a thermocouple is based on the connection of two conductors with different compositions to form a network. If the temperature of the two connection ends is different, a physical phenomenon of thermal current is generated in the circuit.

A thermocouple consists of two different wires (hot electrodes) A and B, with one end T1 welded to each other, forming the measuring end T1 (also known as the working end) of the thermocouple. Insert it into the medium of the measured temperature: while the other end T0 (reference or free end) of the thermocouple is connected to the display instrument. If there is a temperature difference between the measuring end and the reference end of the thermocouple, the display instrument will indicate the thermoelectric potential generated by the thermocouple.

The thermoelectric potential of a thermocouple increases with the temperature at the measuring end, and its magnitude is only related to the material of the thermocouple and the temperature at both ends of the thermocouple, and is independent of the length and diameter of the thermoelectric electrode.

2. Explosion proof principle

The explosion-proof structure of the explosion-proof type is designed and manufactured based on the principle of maximum test safety clearance, through the extinguishing and cooling effects of the explosion-proof joint surface, so that the combustible mixture can explode inside the explosion-proof shell without damaging it, and without causing ignition of external explosive gases.

This product is suitable for explosions caused by the formation of flammable gases or vapors in Zone 1 and Zone 2 with air in the presence of Class IIA, IIB, IIC, T1 to T6 groups

Zone 1 and Zone 2 locations for sexual mixtures.

The model specifications and meanings of thermocouples are as follows:

1. Measurement range: 0~+800 ℃

2. Explosion proof mark: Ex d Ⅱ C T6 Gb

3. Protection level: IP65

4. Division number: Table 1

5. Response time: 90-180s

6. Rated voltage: 24VDC

7. Insulation resistance:

(1) Room temperature insulation resistance: When the ambient air temperature is 15-35 ℃ and the relative humidity is below 80%, the insulation resistance between the thermocouple temperature sensing element and the protective tube is not less than 100M Ω.

(2) High temperature insulation resistance: When the thermocouple is between 300-500 ℃, the insulation resistance between the temperature sensing element and the protective tube shall not be less than 2 M Ω.

8. The environmental conditions for use are as follows:

Atmospheric pressure of 80-110kPa;

B Environmental temperature: -20~40 ℃;

The maximum relative humidity of the ambient air is not greater than 80% (+25 ℃);

Places where explosive mixtures of Zone 1 and Zone 2 flammable gases or vapors with air are present in groups IIA, IIB, IIC, and T1-T6;

In an environment without damaging the insulation with gas or vapor;

In areas without significant shaking or impact vibration;

The basic structure of explosion-proof thermocouples mainly consists of four parts: temperature sensing element components, junction boxes, protective tubes, and installation and fixing devices. The basic structure is shown in the assembly drawing WR.001.1-14.

1. Temperature sensing component assembly

The temperature sensing element of this product is composed of a hot electrode, compensation wire, ceramic insulation tube, wiring socket, etc.

2. Junction box

The box base and lid are made of aluminum alloy with magnesium and titanium content not exceeding 7.5% (by mass percentage) and tensile strength greater than 120N/mm2, and they are connected by threaded explosion-proof joint surfaces. After installing and connecting the external leads, the box cover should be tightened. After being put into use, it is strictly prohibited to open the box cover before disconnecting the thermocouple power supply. Connect the junction box and protective tube with a threaded explosion-proof joint surface. The junction box adopts a compression nut type introduction device, and cables of appropriate size should be used to ensure that the sealing ring of the introduction device can clamp the cable without leaving any gaps.

3. Protective tube

All are made of stainless steel, which has good temperature resistance, corrosion resistance, and sufficient mechanical strength.

The design insertion depth of the protective tube for this model of product is 150mm. In addition, users can provide specific dimensions according to their needs.

4. Install fixing devices

The installation fixing device is nut type fixing or flange type fixing, as shown in Figure WR.008.1-2.

5、 Installation and use

1. Selection of Explosion proof Thermocouples

The correct selection of explosion-proof instruments by users is one of the important conditions for ensuring factory safety, and it also relates to whether the instruments are economical and practical.

(1) Selection principle:

The use of explosion-proof thermocouples by users must be compatible with the level, group, and hazardous area classification of explosive mixtures at the temperature measurement site.

(2) Explosion proof mark

The explosion-proof mark of this product is Ex d Ⅱ C T6 Gb.

2. Installation requirements:

The on-site installation of this product must comply with the relevant provisions of GB3836.15-2000 "Electrical Equipment for Explosive Gas Environments Part 15: Electrical Installation in Hazardous Areas (excluding Coal Mines)" standard.

The installation location of thermocouples should avoid being installed near the furnace door and the heating object. The junction box of the thermocouple should not touch the container wall of the measured medium and should be installed in a well ventilated area. The outlet hole of the thermocouple junction box should be downward to prevent water, dust, and debris from falling into the hole.

3. Wiring:

The junction box is equipped with internal and external grounding screws. To ensure safety, during installation, it is marked with“

Insulated (preferably shielded) copper wire should be used for cable introduction, and the outer diameter of the cable should be compatible with the sealing ring. The cross-sectional area of the copper wire depends on the distance between the thermocouple and the secondary instrument, but should not be less than 1.5mm2. The resistance value of the wire should be registered according to the technical specifications of the secondary instrument (generally 5 Ω).

4. Use of explosion-proof thermocouples:

Using a thermocouple to measure temperature, the thermocouple is installed at the measured location, and after a period of time, the actual temperature at the measured location can be measured. To reduce the heat conduction and exchange between the tested area and the outside world, the circulation of the tested medium should be increased. Under the allowable working pressure conditions, the convective heat transfer between the thermocouple and the tested medium should be increased as much as possible; Increase the insertion depth of thermocouples. When in use, thermocouples should be paired with secondary instruments with corresponding scale marks to correctly display and control temperature. A thermocouple should not be connected to two secondary instruments at the same time.

5. Precautions for use:

(1) Check if there is an explosion-proof mark and explosion-proof certificate number on the obvious part of the product casing.

(2) Check whether there is any mechanical damage to the product during transportation, installation, and other processes, especially the explosion-proof joint surface and anti loosening device, which must not have any damage. If there is damage or looseness, it may affect the explosion-proof performance.

(3) Check whether the explosion-proof category, temperature group, and usage area of the product meet the requirements of the usage location and explosive gas mixture location.

(4) Whether there are internal and external grounding screws and markings.

(5) It is strictly prohibited to arbitrarily change parts related to explosion prevention to ensure their explosion-proof performance.

(6) It is strictly prohibited to open the cover with electricity in hazardous areas. The power supply of the thermocouple must be turned off before opening the cover. After installation, it should be checked for accuracy, the box cover should be tightened, and the anti loosening screws on the box cover should be installed before powering on for use.

(7) The thermocouple can only be removed or replaced when the temperature of its insertion part drops below 80 ℃ or below the temperature limit allowed under the operating conditions.