What are the usage errors of thermocouples?

The correct use of thermocouple can not only get accurate temperature values, ensure the conformity of products, and also can save the cost of thermocouple data, can save money and ensure the quality of products. If the device is incorrect, some errors will occur in the application, so what are these errors after all? The following thermal resistance manufacturers take us to understand the error of thermocouple use.

1, the introduction of thermal inertia error

Because the thermal inertia of the thermocouple can make the indicator value of the instrument lag behind some changes in the measured temperature, this effect is very outstanding when rapid measurement is carried out. Therefore, a thermocouple with thinner thermal electrodes and smaller maintenance tube diameters should be used whenever possible. A more effective approach is to minimize the size of the hot end. In the application, the maintenance casing with good thermal conductivity, thin pipe wall and small inner diameter is usually selected. In some of the more precise temperature measurement, the use of bare wire thermocouple without maintenance casing, but the thermocouple is simple damage, should be corrected and replaced in time.

2, thermal resistance error

At high temperature, if there is a layer of coal ash on the maintenance pipe, the thermal resistance will increase and hinder the conduction of heat. At this time, the temperature indicated value is definitely lower than the actual value of the measured temperature. Therefore, we should adhere to the external cleaning condition of thermocouple maintenance pipe to reduce errors.

3, insulation deterioration and the introduction of errors

If the thermocouple insulation, maintenance pipe and cable plate dirt or salt slag too much, will lead to poor insulation between the thermocouple pole and furnace wall, more serious at high temperature, this will not only cause the loss of thermoelectric potential and will introduce disturbance, therefore, the error caused sometimes can reach 100 degrees.

4. Improper introduction of devices

Such as thermocouple device position and penetration depth can not reflect the actual temperature of the furnace, in other words, thermocouple should not be installed too close to the door and heating place, penetration depth should be at least 8 ~ 10 times the diameter of the maintenance tube; The interval between the thermocouple maintenance tube and the wall is not filled with insulation material, resulting in heat overflow or cold air invasion, so the open space between the thermocouple maintenance tube and the furnace wall hole is blocked with refractory mud or asbestos rope and other insulation materials to avoid cold and hot air convection and affect the accuracy of temperature measurement; The cold end of thermocouple is too close to the furnace body so that the temperature exceeds 100℃; The thermocouple device should try to avoid strong magnetic field and strong electric field, so the thermocouple and power cable should not be installed in the same conduit to avoid introducing disturbance to form errors; The thermocouple can not be installed in the measured medium in the area of little movement, when the thermocouple to measure the temperature of the gas in the tube, the need to make the thermocouple device against the flow direction, and full contact with the gas.

Thermocouple common error basically has above 4 kinds, every kind of error should get attention, after all the measurement accuracy of thermocouple is very important.