I have noted the following voltages on the Laser Filter Cavity (LFC) Ion Pump Controller and the pressure according to the Agilent FRG702 pressure gauge. The voltage corresponds to the current draw by the ion pump. These are only from "steady" times, not when there is a sudden change in the system, for example turning the ion pump on or closing the gate valve to the turbo pump. I graphed this data. The fit appears linear, but the lowest voltage (not steady state) I've seen is 2.1 V when first turning on the controller, so the fit seems good up to ~1.4E-6 Torr. Maybe this is when the current maxes out, assuming a constant current to voltage conversion.
| Pressure (Torr) | Voltage (V) |
| 4.7E-07 | 3.95 |
| 5.1E-07 | 3.93 |
| 4.4E-07 | 4.09 |
| 3.1E-07 | 4.29 |
| 3.0E-07 | 4.32 |
| 2.5E-07 | 4.44 |
| 2.2E-07 | 4.52 |
| 1.4E-07 | 4.67 |
| 2.4E-07 | 4.36 |
| 3.0E-07 | 4.22 |
Updated data. It looks like there are two linear regions. I would expect a linear low pressure region and some rolloff at higher pressures as the ion pump satruates, but I expected the rolloff to be above 1E-6 Torr because the ion pump works at and under 1E-6 Torr.
