How can a thermocouple be used to detect pressure under vacuum?

Question

I work with vacuum tools which use a thermocouple via a Tc board and a software interface to read pressure in millitorr. Just curious exactly how the software does this.

I am talking about 20 year old Applied Materials dep/etch manufacturing tools. A serious question. I would guess that the tool calculates this using it's knowledge of the type and volume of gas flowing through the vacuum chamber?

I have ordered the part and installed it, the box says "Thermocouple Vacuum Gage" and it is calibrated by adjusting voltage on the "TC" board which is plugged into the mainframe and software. It is not a strain gage or a manometer, it is small and it connects with only 4 wires.

Answer 1

hmmm, you're one confused puppy...go back to bed and stop smoking that stuff.

Answer 2

I'm not familiar with this device. However, I can see how a thermocouple might be used to measure pressure. The rate of convective heat transfer through a gaseous medium is related to the pressure. Having more molecules per unit volume allows better transfer than fewer molecules. If a thermocouple were placed a short distance from a heat source, the temperature it would register would relate to the pressure.

Answer 3

I would think the sensing device is a strain gage, rather than a thermocouple. A strain gage could change an attribute like resistance, and the computer could interpret changes in a fashion displayed as pressure.