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Teledyne API - T100 UV Fluorescence SO2 Analyzer Troubleshooting & Service
245
finger over the inlet and see if it gets sucked in by the vacuum or, more properly, use a
flow meter to measure the actual flow. If a proper flow of approximately 650 cm³/min
exists, contact Technical Support. If there is no flow or low flow, continue with the next
step.
Check that the sample pressure is at or around 28 (or about1 in-Hg-A below ambient
atmospheric pressure).
12.3.2. HIGH FLOW
Flows that are significantly higher than the allowed operating range (typically ±10-11%
of the nominal flow) should not occur in the M unless a pressurized sample, zero or span
gas is supplied to the inlet ports. Be sure to vent excess pressure and flow just before the
analyzer inlet ports.
When supplying sample, zero or span gas at ambient pressure, a high flow would
indicate that one or more of the critical flow orifices are physically broken (very
unlikely case), allowing more than nominal flow, or were replaced with an orifice of
wrong specifications. If the flows are more than 15% higher than normal, we
recommend that the technician find and correct the cause of the flow problem,
12.4. CALIBRATION PROBLEMS
This section provides information regarding possible causes of various calibration
problems.
12.4.1. NEGATIVE CONCENTRATIONS
Negative concentration values may be caused due to the following:
A slight, negative signal is normal when the analyzer is operating under zero gas and
the signal is drifting around the zero calibration point. This is caused by the
analyzer’s zero noise and may cause reported concentrations to be negative for a few
seconds at a time down to -5 ppb, but should alternate with similarly high, positive
values.
Mis-calibration is the most likely explanation for negative concentration values. If
the zero air contained some SO
2
gas (contaminated zero air or a worn-out zero air
scrubber) and the analyzer was calibrated to that concentration as “zero”, the
analyzer may report negative values when measuring air that contains little or no
SO
2
. The same problem occurs, if the analyzer was zero-calibrated using ambient air
or span gas.
If the response offset test function for SO
2
(OFFSET) are greater than 150 mV, a
failed PMT or high voltage supply, or sample chamber contamination, could be the
cause.
12.4.2. NO RESPONSE
If the instrument shows no response (display value is near zero) even though sample gas
is supplied properly and the instrument seems to perform correctly,
Confirm response by supplying SO
2
span gas of about 80% of the range value to the
analyzer.
Check the sample flow rate for proper value.
06807C DCN6650