Teledyne 2120 - Trace Nitrogen in Argon Analyzer - Manual (Page 57)

Trace Nitrogen in Argon Analyzer Maintenance
To replace the PMT:
1. Remove the AC power cord from the unit.
2. When removing the PMT cover, the optical filter dislodges from
its position. Remove the PMT cover, carefully catching the
optical filter with gloved hands to avoid getting any fingerprints
on the filter.
3. Remove the PMT.
4. Install the new PMT.
5. Clean the glass surface of the PMT, removing any fingerprints
or dust.
6. Replace the optical filter into the window opening with the
mirror-side out. Hold it in place.
7. Replace the cover on the PMT. Take care to keep the filter and
window lined up with the vertical grid visible within the tube.
5.4.7 High Voltage Plate Adjustment
If the plate voltage to the PMT is too high, a non-linearity problem
will arise where gases in the midrange of the analyzer read higher
than normal. If the plate voltage to the PMT is too low, the analyzer
will run out of span adjustment on the front panel control. For this
reason, the plate voltage to the PMT is critical.
Each new analyzer is tested with a range of gases to determine the
optimum high plate voltage for the PMT. This voltage is adjustable
through the potentiometer, labeled 1 P28 Plate Adjust on the rear panel
of the analyzer. See Figure 1-2.
Adjust this voltage very carefully to eliminate non-linearity
problems. It is normally only adjusted if you run out of span or zero
adjustment on the front panel controls.
5.4.8 High Voltage Transformer
One of the most common failures of the analyzer is an open
secondary winding in the high-voltage transformer. This transformer,
powered by the 255 Hz power supply, supplies ionization voltage to the
analytical cell. The value of high voltage coming from the transformer is
difficult to measure, but an accurate reading is not necessary. To check
the transformer:
Teledyne Analytical Instruments
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