Thermocouple is good when new, but the new factory of K type thermocouple should be how to judge of his? This for some not really familiar with thermocouple customers don't know how to judge, judge the thermocouple is mainly from the following two aspects to judge.
a, the appearance of the thermocouple thermal electrode judgment
1, the new thermocouple, thermal electrode diameter should be homogeneous, flat, surface crack, burr and interlayer; Precious metal thermocouples should not have hot electrode defects, fragile after cleaning should not have serious black spots or phenomenon.
2, thermocouple measuring the welding quality will affect the reliability of temperature measurement, measurement end welding is firm, with metallic luster, smooth surface, no contamination, slag inclusion and crack, etc. , solder joints as far as possible some more small size, the diameter of the solder joints was usually hot twice the diameter of the electrode.
3, all kinds of thermocouple electrode diameter and tolerance is about ( S, R, B: diameter 0. 5 mm, tolerance - 0. 02mm) ; ( 2 K type: diameter. 0mm- 0. 8 mm and a diameter of 2. 5/3 when. 2 - 0. 1mm) 。
thermocouple thermal electrode of appearance quality inspection we usually by visual inspection or with the help of a low-power magnifying glass to observe. Check the accidentally wire diameter, the precision is not lower than 0. 01 mm measuring tool, in the same cross section on the two vertical direction.

2, thermocouple protection tube appearance judgment
1, the thickness of the thermocouple protection tube: want to see the scene of the temperature requirements, minimum thickness of not less than 2 mm.
2, thermocouple protection tube in the production process has some strict requirements: first the head, head has two kinds: one, using the lathe from sealing method, under the high speed advantage is thermocouple protection pipe of equivalent material, the heat resistance and can proper use, the disadvantage is that some bad there will be a hole sealing leakage or leakage, if in the harmful gas or liquid using the consequence is unimaginable. Second, is to use plug seal, which is a plug stuck at the end of the thermocouple protection tube, reoccupy argon arc welded, benefit is under pressure to a few bigger, head thickness uniformity of appearance also is very beautiful; Defect is material does not necessarily equal, if the temperature is high may not satisfied life. Whether it is made of how should conduct stress tests, in case of one thousand has a hole.
3, thermocouple thread welding requirements: some thermocouple with threads, thread material usually choose 1 cr18ni9ti or 304, or with the same thread material protection tube material, now we use high chromium in some small workshops, some manufacturer is thread by way of casting production, and more formal approach is to use equivalent material materials. The car out. Thread of the two must have soldering station, convenient to use argon arc welding. Thread two required welding is firm.
4, the appearance of the thermocouple protection tube processing, in the past few manufacturer in particular, some old instrument, is to keep polishing, polishing is just the external surface behind a layer of protection tube, bright beautiful, but not practical. Now because of the increase in technology of stainless steel tube in the process of production can do finish processing, the production need to do some special treatment on the surface. When a layer of inferior smooth appearance looks very dignified, quality also is not lost.
5, protection tube, no residual dirt and metal scraps.
6, protecting tube should be no significant corrosion and dents and scratches.
7, junction box in the polarity mark correctly.
8, parts assembly should be correct, reliable connection, parts intact.
all in all, according to the above the time to check on the appearance of the thermocouple, we can more intuitive to judge the quality of a thermocouple.