Teledyne 200E, Instruction Manual, Page: 236 / 302

Model 200E Instruction Manual Troubleshooting & Repair
may be necessary to go back and forth between coarse and fine adjustments if the
proper value is at the threshold of the min/max coarse setting.
NOTE
Do not overload the PMT by accidentally setting both adjustment switches to their
maximum setting. Start at the lowest setting and increment slowly. Wait 10
seconds between adjustments.
• If the NORM PMT value set above is now between 790-810, skip this step.
Otherwise, adjust the NORM PMT value with the gain potentiometer down to
800±10 mV (in general: 2x the span gas concentration value in ppb). This is the
final very-fine adjustment.
• Note that during adjustments, the NORM PMT value may be fluctuating, as the
analyzer continues to switch between NO and NO
X
streams as well as between
measure and AutoZero modes. You may have to mentally average the values of NO
and NO
X
response for this adjustment.
• Perform a software span calibration (Section 7.2, 7.4, or7.5) to normalize the sensor
response to its new PMT sensitivity.
• Review the slope and offset values, the slopes should be 1.000±0.300 and the offset
values should be 0.0±20 mV (-20 to +150 mV is allowed).
11.6.6. Replacing the PMT, HVPS or TEC
The photo multiplier tube (PMT) should last for the lifetime of the analyzer. However, in
some cases, the high voltage power supply (HVPS) or the thermo-electric cooler (TEC) may
fail. In case of PMT, HVPS or TEC failure, the sensor assembly needs to be opened in order
to change one of these components. Refer to Figure 1 -7 for the structure of the 200E
sensor assembly and follow the steps below for replacement of one of its components. We
recommend to ensure that the PMT, HVPS or TEC modules are, indeed, faulty to prevent
unnecessary opening of the sensor.
1
• Power down the analyzer, disconnect the power cord, remove the cover and discon-
nect all pneumatic and electrical connections from the sensor assembly.
• Whereas it is possible for a skilled technician to change the PMT or HVPS through the
front panel with the sensor assembly mounted to the analyzer, we recommend to
remove the entire assembly and carry this procedure out on a clean, anti-static table
with the user wearing an anti-static wrist strap to prevent static discharge damage
to the assembly or its circuits.
• If the TEC is to be replaced, remove the reaction cell assembly at this point by
unscrewing two holding screws. This is necessary only if the PMT cold block is to be
removed. This step is not necessary if the HVPS or the PMT only are exchanged.
• Remove the two connectors on the PMT housing end plate facing towards the front
panel. Remove the end plate itself (4 screws with plastic washers). Remove the
dryer packages inside the PMT housing. Along with the plate, slide out the OPTIC
TEST LED and the thermistor that measures the PMT temperature. Both may be
coated with a white, thermal conducting paste. Do not contaminate the inside of the
housing with this grease, as it may contaminate the PMT glass tube on re-assembly.
044100102 Rev A 221