Servicing
PMT Voltage Adjustment
7-18 Model 42i Low Source Instruction Manual Thermo Electron Corporation
5. Remove the four screws securing the power supply to the bracket and
remove the power supply.
6. To install the power supply, follow the previous steps in reverse.
7. Recalibrate the instrument. Refer to the calibration procedures in the
“Calibration” chapter.
PMT Voltage
Adjustment
Use the following procedure to adjust the PMT voltage after switching from
standard to extended ranges or vice versa.
1. Select the NO, NO
2
, and NO
x
ranges. Refer to “Range Menu” in the
“Calibration” chapter.
2. Set the NO BKG and NO
x
BKG calibration factors to 0.0. Refer to
“Calibration Factors Menu” in the “Calibration” chapter.
3. Set the NO COEF, NO
x
COEF, and NO
2
COEF to 1.000.
4. Set the Averaging Time to 10 seconds. Refer to “Averaging Time” in the
“Calibration” chapter.
5. Connect the calibration gas and allow the instrument to sample
calibration gas until the reading stabilizes.
6. From the Main Menu, press to scroll to Service > press >
to scroll to PMT Voltage Adjustment > and press .
The Set PMT Voltage screen appears.
If the Service Mode is not displayed on the Main Menu, use the
following procedure to display it.
WARNING The service procedures in this manual are restricted to qualified
service representatives.
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