The choice of the thermocouple method

Thermocouple are two different conductors connected together to form,

thermocouple ( Figure 13)

when measurement and reference points respectively in different temperature on the produce the so-called thermoelectric magnetic ( EMF) 。 Join point use measuring points is measured temperature in the portion of the thermocouple connection point. Reference points is kept at a known temperature, or can automatically compensate the temperature change of the thermocouple connection part.

in normal industrial applications, the 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. The join 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 * better response time, but * * Yu Zaifei corrosion, not dangerous and not use pressure applications. Response time to time constant, time constant is defined as a sensor in the accused of environment change 63 between initial value and final value. The time needed for 2%. Dew end thermocouple with * fast response speed, and the smaller the probe sheath diameter, the response speed is faster, but its big * allows 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 connect right, extension lines will reference points from the other end of the thermocouple transfer to line, which is typically located at one end was accused of environment.

select thermocouple choosing thermocouple to consider the following factors:

1, the measured temperature range.

2, the required response time;

3, the join type;

4, thermocouple or sheath material chemical corrosion resistance;

5, resistance to wear and tear or the ability to resist vibration;

6, installation and limit requirements, etc.