What are the usage errors of thermocouples?

The correct use of thermocouple can not only get accurate temperature values, ensure the conformity of products, but also save the material consumption of thermocouple, which can save money and ensure the quality of products. If, the device is incorrect, can produce some errors in using, so, what are these errors after all? The following thermal resistance manufacturers take you to understand the error of thermocouple use.

1, the introduction of thermal inertia error

Because the thermal inertia of the thermocouple can cause the indicator value of the meter to lag behind some changes in the temperature being measured, this effect is prominent when rapid measurements are made. Therefore, a thermocouple with thinner thermal electrodes and smaller maintenance tube diameters should be used whenever possible. A more effective method 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 delicate temperature measurements, bare-wire thermocouples without maintenance bushing are used. However, thermocouples are easily damaged and should be checked 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, the external cleanliness of the thermocouple maintenance pipe should be maintained to reduce errors.

3, insulation deterioration and the introduction of errors

If the thermocouple insulation, maintenance pipe and wire 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 interference, therefore, the error caused sometimes can reach 100 degrees.

4. Improper introduction of devices

Such as the position of the thermocouple device and insertion depth can not reflect the actual temperature of the furnace, in other words, the thermocouple should not be installed in too close to the door and heating place, insertion depth should be at least 8 ~ 10 times the diameter of the maintenance tube; The distance between the thermocouple maintenance sleeve and the wall is not filled with insulation material, resulting in heat overflow or cold air invasion, so the gap between the thermocouple maintenance tube and the furnace wall hole is blocked with refractory mud or asbestos rope insulation material 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 interference caused by errors; The thermocouple should not be installed in the area where the measured medium rarely flows. When the thermocouple is used to measure the temperature of the gas in the tube, the thermocouple should be installed against the direction of the flow rate and fully in contact with the gas.

Thermocouple common errors mainly have above 4 kinds, each error should be paid attention to, after all, the thermocouple measurement accuracy is very important.