Maintenance and Troubleshooting | 6-35
PMT Level and PMT Balance
PMT Level and PMT Balance are adjusted only during the Auto-
Setup sequence. The typical range of operation for both parameters is
0–10000 mV. After a successful Auto-Setup, the PMT Level should be
7200–7400 mV while the PMT Balance should be 2000–8000 mV. The
analyzer will function with values outside this range, but it is a sign that a
change has likely occurred in the transmission of light within the Optical
Bench (for example: dirty windows, weak lamps, weak PMTs, faulty PMT
Buffer board) – see “Troubleshooting and Diagnostics” in this chapter for
alarm conditions and corrective action.
At the end of every Auto-Setup, always check the PMT Level and PMT
Balance. Take note of severe changes in PMT Level and PMT Balance
because they are as important as the absolute value.
The PMT Level signal adjusts the gain of both PMTs simultaneously in
the same direction. PMT Balance adjusts the gain of the two PMTs in
opposite directions by controlling a virtual ground circuit on the Optical
Bench board.
If the PMT signals are outside their normal range of operation after the
Auto-Setup is complete, check for the following:
• Adjust the Lamp Max setting slightly (typical range is 4500–7800 mV)
and start another Auto-Setup.
• Was the Auto-Setup done with Zero gas flowing through the sample
system?
• Are the Measuring Cell Windows clean?
• Are the PMT signals weak?
• Are the PMTs in their original Lamp Sockets (is the higher gain PMT in
the Measure path)?
• Is the PMT Buffer board faulty?
• Do the source lamps need replacement (weak lamps)? If not, are the
source lamps aligned?
• If the lamps were replaced, is the correct Lamp Socket connected to
the correct lamp? Lamp 1 is the closest to the Optical Bench board.
• Have there been any leaks from the Measuring Cell? If so, check the
condition of the Optical Filters, Beam Splitter, Mirrors, Windows,
Lenses, and o-rings in the Optical Bench and in the Measuring Cell
(including Reflector Block). Contact AMETEK for procedures not dis-
cussed in this manual.
See “Troubleshooting and Diagnostics” in this chapter for alarm con-
ditions and corrective action.

NOTE
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