“Electrons boil from the hot filament (30Vdc) and are accelerated towards the anode grid (180Vdc). As the current (0.1-10 mA typical) of highly energetic (150eV) electrons traverse the inner volume of the grid cage, they ionize some of the gas molecules they encounter in their path. Electrons that do not encounter any obstacles in their path exit the grid and are immediately directed back into its inner volume by the electrostatic field, resulting in a multiple pass ionization path that ultimately ends by collision with a grid wire. The ions formed inside the anode grid are efficiently collected by the grounded (0Vdc) collector wire that is located along the axis of the cylindrical grid and connected to the controller's electrometer” If the electron emission current and the temperature of the gas are constant, then the ion current is proportional to the number density and the pressure of the gas.“ [Appendix A]


Has a separate power supply and digital side. RS-232 interface option.

Just from reading the manual sounds a little quirky…has some notes like that LED display is closely tied to the RS-232 output even when it doesn't always make sense.


I purchased this unit because they are widely available on the surplus market and are a relatively inexpensive unit with computer interface option.

“307 VGC Cable Connections” [307 manual 1-9 (Figure 1-7). copyright Granville-Phillips]:

The DA-15 male-male connector between the two units is straight through. Shields are connected on both D-sub connector sides but are not connected to any pins.

“Degas can not be activated unless the IG pressure is below 5 x 10-5 in torr/mbar units, or 6.6 x 10-3 in pascal units.” The IG will also turn off after a few seconds if too high of pressure is detected (above 10-4 torr or maybe it as 10-5 torr). Warning: if the collector cable is disconnected it will read something like 10-9 torr.

Power supply

WARNING: there are jumpers on the PCB that must be set correctly for given line voltage…the PS is NOT auto-ranging

1 and 2 port versions available. Each port can control one ion gauge. The collector (vacuum level signal) is connected separately to the controller instead of through the tube power connector.

“Standard Tube Base Configurations” [307 manual 1-8 (Figure 1-6). copyright Granville-Phillips]:

My gauge (CES (ETI?) 8136F):

From left to right:

Pin Signal Notes
1 Anode grid
2 Filament
3 (raised) N/C Structural: supports top of anode grid. Electrically disconnected at STP
4 Filament
5 Anode grid


Convectron tubes

Looks like its designed for GP-275 tubes although the manual just says “Convectron” tubes. Note that there is a module and a bare tube variant. I believe that the module contains a bare tube except that it doesn't have the blue sheath. More than likely you could steal one from another if need be

Seems that Duniway Stockroom Corp. CVT-275-101 is a third party alternative.


equipment/vacuum/gp/igc.txt · Last modified: 2013/10/20 14:59 by
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