How to judge the quality of a thermocouple from its appearance

Because thermocouples directly interact with the measured medium and are not affected by adjacent links, their measurement accuracy is high, making them one of the most commonly used temperature detection sensors in industry, public use, experimentation, and scientific research. Therefore, thermocouples are the most commonly used temperature instruments. Thermocouples not only have high measurement accuracy but also a wide measurement range. Thermocouples can continuously measure from negative 80 degrees to positive 2300 degrees, and some special thermocouples may have a wider range.

So, how can we determine the quality of thermocouples directly from the surface? Let's listen to the skilled staff of China Sensor Trading Network talk to you about the scales of determination.

1, Surface determination of thermocouple hot electrode

1. The new thermocouple should have an even and straight hot electrode diameter, with no cracks, burrs, or interlayers in name; Precious metal thermocouples should not have the disadvantage of weak thermoelectric electrodes, and there should be no severe color spots or blackening after cleaning.

2. Thermocouple measurement of welding quality can affect the reliability of temperature measurement. It is requested that the measuring end be welded firmly, with metallic light, nominal oil slip, no contamination, degradation, slag inclusion, cracks, etc. The size of the welding point should be small, and the diameter of the welding point should be twice the diameter of the thermoelectric electrode on a regular basis.

3. The electrode diameter and tolerance of various thermocouples are generally (S, R, B types: diameter 0.5mm, tolerance -0.02mm); (K-type: diameter 2.0mm-0.08mm, diameter 2.5/3.2-0.1mm).

The review of the surface quality of thermocouple hot electrodes is conducted by visual inspection or by using a low-power magnifying glass. When reviewing the diameter of a pair of wires, use a measuring tool with an accuracy of not less than 0.01mm to measure at two perpendicular deviations of the same cross-section.

2, Determination of thermocouple maintenance tube surface

1. The thickness of the thermocouple maintenance tube should depend on the temperature requirements on site, and the minimum thickness should not be less than 2mm.

2. There are some strict requirements for the maintenance of thermocouple tubes in the production process: first, the head. There are two types of heads: first, stop the self melting sealing method with a lathe at high speed. The benefit is that the thermocouple and the protective tube are made of the same material, and can withstand temperature and be applied appropriately. The problem is that some seals are not good enough, which can easily cause air holes or water leakage. If used in gas or harmless liquids, the results will be unimaginable. 2, It is sealed with a plug, that is, a plug is placed at the end of the thermocouple maintenance tube, and then welded firmly with argon arc welding. The benefit is that it can withstand more pressure, and the average thickness and surface of the head are also beautiful; The problem is that the materials are inconsistent and suitable, and if the temperature is high, the service life may not be sufficient to meet the requirements. Regardless of the manufacturing method used, pressure testing should be stopped in case of any air pockets.

3. Thread welding requirements for thermocouples: Some thermocouples require threads, and the material of the threads is usually 1Cr18Ni9Ti or 304, or thread materials similar to the maintenance pipe material. Initially, some small workshops used high chromium, while some manufacturers produced threads by casting. The more formal approach is to use materials that match the material. Car out. The two ends of the thread must have a welding station for easy argon arc welding. The two ends of the thread must be welded firmly.

4. The surface treatment of thermocouple maintenance tubes was not allowed to be polished in some previous manufacturers, especially some experienced instrument workers. Polishing only involves dropping the surface layer of the maintenance tube, which is bright and unsightly, but not suitable. Initially, due to technological advancements, stainless steel pipes were able to undergo brightness treatment during the production process. During production, a special treatment was applied under the guise, resulting in a matte finish on the surface that looked tasteful without compromising quality.

5. Maintain no residual dirt or metal debris inside the pipe.

6. There should be no obvious corrosion, dents, or scratches outside the maintenance pipe.

7. The polarity labeling in the junction box is accurate.

8. The disassembly of each component should be accurate, the connection should be secure, and the entire machine should be undamaged.

In short, by examining the surface of a thermocouple based on the above points, we can fairly determine the quality of a thermocouple.