6-38 | Model 933S UV Analyzer
Manipulating the PMT Level and PMT Balance
In certain situations (for example: degradation of PMTs or lamps, or the
optics are contaminated), it may be necessary to change the P300 and
P301 jumper settings on the Optical Bench board. Changing the jumper
positions provides coarse gain adjustment of the Reference PMT and there-
fore changes the PMT Level and PMT Balance.
There are six jumper positions (four in P300 and two in P301) – at least
one jumper must be in one of the six positions at all times. The jumper
combinations control the coarse supply voltage ranges of the two PMTs,
Reference-path and Measure-path. The Optical Bench Auto-Setup proce-
dure performs fine adjustment to the PMT supply voltages at one jumper
combination. The jumper combinations affect the Auto-Setup in terms of
increasing or decreasing the resulting PMT Balance and, to a lesser de-
gree, the PMT Level.
Figure 6-11 describes the effect on the PMT Balance and PMT Gain in rela-
tion to different jumper positions.
To achieve an acceptable PMT Balance and PMT Level:
1. If jumpers have been reconfigured, perform an Auto-Setup.
If the PMT signals are outside their normal range of operation after
the Auto-Setup is complete (typical range is 4500–7800 mVDC),
adjust the Lamp Max setting slightly and start another Auto-Setup.
2. After an acceptable PMT Balance and PMT Level has been achieved,
change the Flow Control to ‘3’ (zero) and initiate a Manual Zero then
click OK. Do not save the changes to EEPROM. Allow the Zero gas to
flow for 2–3 minutes.
From the Status tab observe the Calibration/Solenoid Status field to
view the progress of the Zero calibration.
3. After the Zero is complete, change the Flow Control back to ‘0’ (auto).
Click OK then Apply. Save the changes to EEPROM.
4. From the Status tab, click Conc. Alarm Soft Enable On/Off to Enable
the Concentration Alarms then click OK.
NOTE
Setup (tab)Optical
Setup (tab)Gas
Calibration<<Lamp Max>>
Setup (tab)
Gas Calibration<<Flow
Control>>
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