Pirani gauge sensors have a filament that forms one leg of a wheatstone bridge. The adjacent leg is a compensating resistor that is also part of the sensor. The mode of operation of the sensor is that the filament is maintained at a constant temperature by varying the power as pressure changes (higher pressure more power, lower pressure less power).
In the G-P Convectron the bridge circuit and its electronics are in the controller. Thus you have to replicate the circuitry. (If you really want, I could email you a tif of the schematic. The circuit calls out one OP-07, a 358, a transistor, 3 diodes, and a handful of common caps, resistors and pots.)
I am only familiar with one other convection enhanced Pirani, the one made by MKS/HPS. It has the bridge circuitry as part of the tube - you apply power and read out the voltage directy. Then all you need is a table with the pressure to voltage correspondence (it's very non-linear).
Also, remember Pirani gauges (and t/c and ion gauges) are gas-type sensitive. The standard nitrogen cal means nothing with deuterium or any other gas. However, the G-P manual does have cal curves for a variety of gases including deuterium.
Steve
Created on Monday, February 19, 2001 5:13 PM EDT by Steve Hansen