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I am looking for guidance on how to successfully measure vacuum using a device similar to a pirani gauge, my device however is a tungsten filament which is heated electrically to about 90*C, and it's current draw is a measure of vacuum.The problem I am having is how to relate specifically the current draw to a particular pressure in the system. I know the current draw is inversely-proportional to the resistance, and the resistance varies with the filament temperature, and the temperature varies with gas pressure, warming as the pressure drops due to less thermal conduction and convection.
Running this in my hobby vacuum setup, it is amazingly sensitive. My particular filament running on 5v reads 46.7 milliamps at 28*C 100kPa, and ~38.1 milliamps as I approach 5pa. But I don't know this minimum pressure yet without an accurate gauge.
I really need a mathematical model than will tell me the temperature of a tungsten filament given the ambient temperature, power consumption, and pressure. Thanks for any help!Here is how the pressure and current relate at higher pressures:
This test was done with 3.3 volts, vs 5 volts above(corrected).
ma kPa
36.17 100
35.99 86.8
35.99 76.7
35.73 60.5
35.46 47.4
35.05 34.2
34.35 21.1
33.88 7.9
~32.2 nearly 0
Running this in my hobby vacuum setup, it is amazingly sensitive. My particular filament running on 5v reads 46.7 milliamps at 28*C 100kPa, and ~38.1 milliamps as I approach 5pa. But I don't know this minimum pressure yet without an accurate gauge.
I really need a mathematical model than will tell me the temperature of a tungsten filament given the ambient temperature, power consumption, and pressure. Thanks for any help!Here is how the pressure and current relate at higher pressures:
This test was done with 3.3 volts, vs 5 volts above(corrected).
ma kPa
36.17 100
35.99 86.8
35.99 76.7
35.73 60.5
35.46 47.4
35.05 34.2
34.35 21.1
33.88 7.9
~32.2 nearly 0
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