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page 12 Model 2002
Maintainance and Repair 4-3
the power level of the tube and adjust the proper coefficient for pressure level of the adjustment.
The CAL MODE presupposes that the operator is applying a known pressure of the correct gas
composition (see GAS MODE). The factory calibration points are 800 Torr, 7 Torr, and <1e-6
Torr. The users calibration points are not required to be exactly those values, but should be
somewhat close, and must be within the ranges shown in the following figure. The HPM-2002
detects the voltage signal within the sensor tube, which is converted and displayed as a pressure
reading. The resulting pressure reading determines which of the three coefficients will be ad-
justed.
To adjust a calibration coefficient press the MODE switch until the CAL light is illuminated.
Then simultaneously press the UP and DOWN switch. The CAL light will now flash indicating
that the interlock has been bypassed and the calibration can be adjusted. Press and hold the UP
switch to increase the displayed value or the DOWN switch to decrease the displayed value. If
the switch is held down for an extended period of time the adjustment rate will start to increase.
Release the switch and then press and hold again to regain finer control of the displayed number.
An important point to be noted is the fact that after the adjustment, the new calibration coeffi-
cient is only in temporary memory. If the instrument were unplugged at this point, it would revert