Are Vacuum Thermocouple Tubes a Commodity?
You can buy vacuum thermocouple tubes from dozens of companies. Are they all the same? If you are concerned with measurement repeatability, the short answer is "no."
The heart of a vacuum thermocouple tube is two dissimilar noble metal wires that are formed into a junction. Power is applied, and as the vacuum level improves, the junction emits more electrons and a non-linear signal results.
Which would you rather see on the inside of your gauge tube, this:
or this?:
In addition to longer tube life, the major benefit of the second design is much better repeatability. If you lay the signals of several gauge tubes of the same nominal range over each other, the graph should look something like this:
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