DCC公司工程师对热电偶焊接误区的解释

Hi Mary,

Surely, thermocouple wires are used to measure the temperature while for which measuring precision is a most vital criterion. And another fact is carbon blocks play the role of electrodes. Then my questions are:

1、Can carbon blocks be easily worn down and should they be replaced regularly?

 The weld is accomplished so fast that there is little wear. Mechanical abuse or loss are the chief cause of replacement.

焊接在瞬间完成，所以磨损微乎其微。机械损伤才是更换的主要原因。

2、Can the welding joints of thermocouple wires possibly contain any impurities (carbon or others) from carbon blocks after being welded?

3、If so (see Q. No. 2), shall the impurities left on the carbon block affect the following welding performance and would other wires become impure also? And then what about the precision?

The welded joint contains compounds of carbon and oxygen and nitrogen and other elements. Since the welded joint is at a uniform temperature (isothermal), no thermoelectric voltages are generated by these impurities. Thermocouple voltages are produced by temperature changes (gradient) along the wires themselves and not at the junction, which is an electrical short circuit. The bead itself is a very unique alloy made up of unknown proportions of each wire in the pair, and produces no voltage. The oxygen in air is the chief concern with welding performance, particularly for T type couples. Argon is sometimes used with this wire type readings.

 焊接头（焊缝;焊点）含有碳、氧、氮及其他元素的化合物。焊接头温度均衡（等温）， （焊接头所含的）杂质不会由于温差而产生电压差。热电偶电压是由于热电偶线本身温度改变而产生，而不是焊接头（焊缝），焊接头部分处于短路。（焊接出来的）小球本身就是非常特别的由每根热电偶线产生的合金，但其各成分所占比例不详；小球不产生电压、 空气中的（Oxygen）氧是影响焊接效果的主要原因，尤其是在焊接T型热电偶线,所以有时候在焊接T-type 热电偶时会用到氩气（Argon）。

4、If not, (See Q. No.2 also), could you have us any well-found proof or something like related testing data?

For those knowledgeable about thermocouple effects, it is well known that without a temperature gradient, no thermoelectric voltage can be produced. The bead is not a p/n semiconductor junction or solar cell. It is a short circuit at the end of the wire pair. You can put anything into the alloy without effect. A review of the classic thermocouple theory by the customer could clear up these concerns.

对于热电偶效应方面的知识，众所周知，只要温度不变，就不会产生温差电压。小球既不是半导体，也不是太阳能电池，只是两根热电偶线接头所形成的短路。因此可以在合金（小球）里加入任何东西而不影响最终效果。从客户那里看一下关于热电偶的经典理论，这些问题便会迎刃而解。

5、Is there any substitute for carbon block? The fact is that we have a piece of similar home product which could work things out without a carbon block but ensuring high precision for being free from impurities. So do you happen to have such kind of welders in US? By the way, we are still studying its working principle and got nothing for the present.

6、If we have to use the carbon block, how can we improve the welding precision by means of, say, hand operation or whatever else? 

 Any conductor could be used for the carbon block. Carbon is used since it is inexpensive and will not melt like a metal conductor. Those welders, like inert gas welders (TIG) or spot welders, which use only the thermocouple wire during welding, also produce a very unique alloy in the joint area that does not appear on any thermocouple chart. Fortunately, as stated above, the weld of any kind make no contribution to the thermocouple voltage. The accuracy of the thermocouple sensor is determined by the accuracy of the wire used. If the produced junction is sound electrically and mechanically, the type of weld or impurities in the junctions itself have no effect on the accuracy and certainly no improvement in accuracy.

任何导体都可以用作碳砖。我们之所以使用碳砖，其一：价格低廉；其二：不会像金属导体熔化。那些焊接机，像惰性气体焊接机（TIG）或点焊接机，焊接的时候只使用热电偶线，并在焊接头部分产生一种独一无二的合金；合金不会在任何热电偶图表上。幸运的是，如上所说，任何一种焊接机都不会改变热电偶电压。所用的热电偶线的准确性决定热电偶传感器的准确度。如果所产生的焊点（接头）在电力和机械方面都比较可靠，接头的焊接类型或接头内部的杂质丝毫不会降低焊接精度，当然也不会提高焊接精度。