Gas thermocouples are two different conductors connected together to form, when the measurement and reference points respectively in different temperature on the produce of the so-called thermoelectric magnetic force (EMF). Join point use measuring points is measured temperature of the gas in the thermocouple connection part. Reference points is kept at a known temperature, thermocouple connection or can automatically compensate the temperature change of the gas.
In industrial applications, the conventional gas thermocouple elements general termination on the connector; But very few reference points on the joint, but using appropriate extension thermocouple wire transfer to call temperature relatively stable was charged with environment. Connection type hull thermocouple physical connection points and probe wall (welding), it can achieve good heat transport - the wall would transmit the heat from the outside, through the probe to the thermocouple connection point. Suggest using hull thermocouple to measure static or corrosive gas flow and the temperature of the liquid, and some high voltage applications. In insulated thermocouple, thermocouple connection point is separated from probe wall and surrounded by a soft powder. Although the response speed of the insulated thermocouple slower than the response speed of the thermocouple by shell, but it can provide the electric insulation. It is recommended to use insulated thermocouple to measure the corrosive environment, can be ideally by shielding to the thermocouple sheath with the surrounding environment fully electric insulation. Dew thermocouple allowed to join the tip into the surrounding environment, this type can provide the best response time, but only in the corrosion, not dangerous and not use pressure applications. Response time to time constant, time constant is defined as a sensor in the accused environment between the initial value and final value to change the time required to 63.2%. Dew end thermocouple has fast response speed, and the smaller the probe sheath diameter, the response speed is faster, but the maximum allowable measuring temperature will be low. Line extension thermocouple line extension is a pair is connected with thermocouple temperature electromagnetic frequency characteristics of the same line. When connecting the right line extension will reference points from the gas on the other side of the thermocouple transfer to line, which is typically located at one end was accused of environment.
When choosing gas thermocouples choose thermocouple to consider the following factors:
1, the measured temperature range;
2, the required response time;
3, the types of connection point;
4, thermocouple or sheath material chemical corrosion resistance;
5, resistance to wear and tear or vibration resistance;
6, installation and limit requirements, etc.