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PHOTOMULTIPLIER TUBE (PMT) SENSOR MODULE
The PMT detects the light emitted by the reaction of NO with ozone. It has a gain of about
500,000 to 1,000,000. It is not possible to test the detector outside of the instrument in the
field. The basic method to diagnose a PMT fault is to eliminate the other components using
ETEST, OTEST and specific tests for other sub-assemblies.
O
T
PTIC
EST
The optic test function tests the response of the PMT sensor by turning on an LED located
in the cooling block of the PMT (see Figure 5-20). The analyzer uses the light emitted from
the LED to test its photo-electronic subsystem, including the PMT and the current to
voltage converter on the pre-amplifier board.
•
To ensure that the analyzer measures only the light coming from the LED, the
analyzer should be supplied with zero air.
•
The optic test should produce a PMT signal of about 2000±1000 mV.
To activate the optics test, go to the Utilities>Diagnostics>OE Test menu and press the
Run OTest button.
Note
E
LECTRICAL
The electrical test function creates a current, which is substituted for the PMT signal and
feeds it into the preamplifier board.
•
This signal is generated by circuitry on the pre-amplifier board itself and tests the
filtering and amplification functions of that assembly along with the A/D converter on
the motherboard.
•
It does not test the PMT itself.
•
The electrical test should produce a PMT signal of about 2000 ±1000 mV.
To activate the electrical test, go to the Utilities>Diagnostics>OETest menu and press the
Run ETest button.
PMT PREAMPLIFIER BOARD
To check the correct operation of the preamplifier board, perform an optics test
(Utilities>Diagnostics>OE
(Utilities>Diagnostics>OE Test>Run ETest) described in Section 5.7.9.11 above.
If the instrument passes the OTEST but fails the ETEST, the preamplifier board may
•
be faulty or need a hardware calibration.
083730200A DCN7962
(OT
)
EST
This is a coarse test for functionality and not an accurate
calibration tool. The resulting PMT signal can vary significantly
over time and also changes with low-level calibration.
T
(ET
)
EST
EST
Test>Run
Teledyne API T200 NO/NO
OTest)
and
an
/NO
Analyzer with NumaView™ Software
2
x
electrical
test
161
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Troubleshooting
