2000-OSM, F1 6-5
Perform Test Procedure 11 (Common Usage of Gases), Test Procedure 13 (Burner Air Catalytic
Cleanup Unit), or Test Procedure 14 (Coaxial Cable), as applicable. Replace or clean the FID (see
"FID REPAIR" in Section 8).
Signal Offset (FPD)
NOTE
Because of the sulfur addition in the FPD detector, the FPD will always have a
background level. The auto zero circuitry compensates for this. The background
will usually use 15% to 80% of the available auto zero range. If the background
uses less than 10% of the auto zero range, the flame detection electronics will
assume the flame is out and the Flame Out LED will illuminate. Eluting peaks add
to this background.
Symptom
: Detector signal is continually offset by a significantly different amount than when the
detector was operating properly.
Cause
: Baseline offset problems in an FPD can be caused by the following:
1. Incorrect temperatures. Perform Test Procedure 30 (Checking Temperature Table Values),
steps 1 to 3, 8, and 9. Inspect temperature settings and adjust if necessary.
2. Column flooded with liquid sample. Perform Test Procedure 3 (Sample Valve Leaking/Column
Flooding).
3. A continuous presence of sample at the detector due to sample valve leakage. Perform Test
Procedure 3 (Sample Valve Leaking/Column Flooding).
4. Electronics circuit failure. Replace FPD Amplifier Assembly.
5. Empty or leaking permeation device.
Signal Random Baseline Noise (FPD)
NOTE
Because of the sulfur addition in the FPD detector, the FPD will always have a
background level. The auto zero circuitry compensates for this. The background
will usually use 15% to 80% of the available auto zero range. If the background
uses less than 10% of the auto zero range, the flame detection electronics will
assume the flame is out and the Flame Out LED will illuminate. Eluting peaks add
to this background.
Symptom
: Baseline characterized by random noise and/or spikes (see Figure 6-7).
NORMAL NOISE
Figure 6-7. BASELINE RANDOM NOISE
Cause
: FPD noise is generally the result of electrical noise or contamination.
1. Electrical noise is usually isolated to a defective FPD amplifier, defective coaxial cable or faulty
electrical connections.
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