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HPM-2002-OBEVacuum Gauge Page 14 of 39
OBE will continuously monitor the pressure, update the alarm conditions, and update both analog output
channels about ten times a second.
3.2.4. Cal Mode
Optimal performance of the HPM-2002-OBE is achieved by performing in situ adjustments to the
calibration coefficients in the Cal mode. There are three calibration coefficients. These are the zero coefficient,
the midrange coefficient, and the atmosphere coefficient. Once a tube has been fully calibrated the midrange
coefficient should never need further adjustment, but it may be helpful to adjust the zero coefficient or the
atmosphere coefficient under certain circumstances.
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 < 10
-6
Torr. The
user’s 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-OBE 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 adjusted
The operator action is the same for adjustment of all three of the coefficients, except that he must apply the
proper calibration pressures according to the calibration point he is about to adjust. To adjust a calibration
coefficient, place the HPM-2002-OBE in the Cal mode using the SELECT button. Then turn the ADJUST
rotary encoder. The Cal light will begin to flash during adjustment and will continue to flash until the Cal mode
is exited using the SELECT button.