Working principle

The structure and principle of explosion-proof thermocouples are basically the same as those of prefabricated thermocouples. The difference is that the explosion-proof product junction box (housing) adopts a special explosion-proof structure in the design. The junction box is made of high-strength aluminum alloy die-casting, and the well has sufficient internal space, wall thickness, and mechanical strength. The thermal stability of the rubber sealing ring meets the national explosion-proof standards. So, when the explosive mixed gas inside the junction box explodes, its internal pressure will not damage the junction box, and the resulting heat energy cannot spread or explode outward.

Main technical indicators

1. Temperature measurement range and allowable error

2. Hot response time

When there is a step change in temperature, the time required for the output of the thermocouple to change to 50% of the step change is called the thermal response time, represented by T0.5.

3. Nominal pressure

Generally refers to the static external pressure that the protective tube can withstand at room temperature without breaking, and the test pressure gauge generally uses 1 In fact, the allowable working pressure is not only related to the material, diameter, and wall thickness of the protective tube, but also to its structural form, installation method, insertion depth, and the flow rate and type of the measured medium.

4. Thermocouple insulation resistance

The test voltage for room temperature insulation resistance is DC 500V ± 50V. The atmospheric conditions for measuring room temperature insulation resistance are temperature of 15-35 ℃, relative humidity of 45%, and atmospheric pressure of 86-106kPa.
For thermocouples with a length exceeding 1 meter, the product of their insulation resistance at room temperature and their length should not be less than 100M Ω. Namely: R r- L > 100M Ω L>l m
In the formula: R r - the insulation resistance value of the thermocouple at room temperature, M Ω;
L - length of thermocouple, m。
For thermocouples with a length of l meters or less, their insulation resistance at room temperature should not be less than 100M Ω.

5. Insulation resistance of armored thermocouple (insulated type)

When the ambient temperature is 20 ± 15 ℃ and the relative temperature is not greater than 80%, the insulation resistance between the thermoelectric electrode and the outer sleeve should be greater than or equal to 1000M Ω - M *, and the test voltage is 500V DC. The insulation resistance M Ω - M represents the product of the insulation resistance at room temperature and the length of the armored thermocouple.

6. Explosion proof type and level group

Explosion proof level group: d II BT4 or d II CT4
D II BT6 or d II CT6
Shell protection level: IP65

7. Explosion proof marking method for explosion-proof thermocouples

8. Description of categories, levels, and temperature groups of electrical equipment

Electrical equipment is divided into two categories: Category I - Electrical equipment used underground in coal mines
Class II - Factory Electrical Equipment

9. Explosion proof grade

The explosion-proof level of explosion-proof thermocouples is divided into three levels: A, B, and C, based on the maximum safe gap or minimum ignition current ratio applicable to explosive gas mixtures.

10. Temperature group

The temperature groups of explosion-proof thermocouples are divided into six groups, T1 to T6, according to the highest surface temperature of their exposed parts.

Characteristic features

Design according to the latest explosion-proof regulations GB3836 that comply with international IEC standards;
Adopting a two chamber explosion-proof structure, it is easy to replace temperature measuring elements and safe and reliable to use
Explosion proof mark d Ⅱ CT6, suitable for temperature measurement in environments with Class IIC or below, ignition temperature T6 or above, and containing explosive gases.
Attention: Please disconnect the power during maintenance and repair

Nominal pressure of thermocouple

Generally refers to the static external pressure that the protective tube can withstand at working temperature without breaking. In fact, the allowable working pressure is not only related to the material, diameter, and wall thickness of the protective tube, but also to its structural form, installation method, insertion depth, as well as the flow rate and type of the measured medium.

Minimum insertion depth of thermocouple

It should not be less than 8-10 times the outer diameter of its protective tube (except for special products).

Structure of Thermocouples

From the temperature measurement principle of thermocouples, it can be known that in addition to the two thermoelectric electrode materials, the most basic thermocouple must also be made into measuring and reference ends at both ends of the thermoelectric electrode according to requirements, commonly known as the "hot end" and "cold end", which are the so-called "two ends".
According to the different uses of thermocouples, there are four forms of the hot end: insulated, multi branch insulated, shell connected, and exposed. The cold end has two forms: sealed and unsealed.
Thermocouples are generally composed of five parts. Two thermoelectric electrodes (or wires) are the core part of the thermocouple (the first part is the temperature measuring element), and the other parts are spread around it. In order to ensure that the thermoelectric potential in the circuit is not lost and the measured temperature signal is accurately transmitted, insulation materials must be used to ensure reliable insulation between the two thermoelectric electrodes except for the two endpoints and between them and the outside world (the second part is insulation materials); In order to protect the insulation material and thermocouple wires and extend the service life of thermocouples, protective sleeves (Part III protective sleeves) are generally designed; In order to facilitate installation and wiring, and to adapt to various usage scenarios, a fourth part wiring device and a fifth part installation fixing device are generally designed. These are the so-called 'Five Parts'. According to different purposes, the most basic thermocouple (i.e. thermocouple core) that can measure temperature does not have protective tubes or fixed installation devices. Prefabricated thermocouples are mainly composed of a junction box, protective tube, insulating sleeve, terminal block, and thermoelectric electrode, and are equipped with various installation and fixing devices.

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Types and specifications of explosion-proof thermocouples

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