Baseline Continuous Noise; Baseline Or Signal Offset (Fid) - ABB PGC2000 Operation And Service Manual

Perform Test Procedure 3 (Sample Valve Leaking/Column Flooding); or Test Procedure 30
(Checking Temperature Table Values), steps 1 to 3, 8, and 9.
Another possible cause could be detector filament deterioration.

Baseline Continuous Noise

Symptom: Baseline (detector signal) with no sample injection appears as noise similar in appearance
to "grass" on a two dimensional drawing on the graphics display or strip chart recorder (if used), as
shown in Figure 6-4. If it is present only on the strip chart recorder, verify the recorder is functioning
properly and that the recorder connecting wires are properly shielded. Ensure recorder wire shield is
connected to ground at only one end.
Cause: Baseline or detector noise can result from contaminated carrier, makeup gas, tubing or
regulators. This type of contamination is much less pronounced with a TCD than for an FID. Other
causes include defective filaments (TCD), detector wiring, or electrical noise in the detector
electronics or power supplies.
Perform Test Procedure 11 (Common Usage of Gases); Test Procedure 12 (Utility Gas
Contamination Procedure); Test Procedure 13 (Burner Air Catalytic Cleanup Unit), and Test
Procedure 14 (Coaxial Cable), as applicable.

Baseline or Signal Offset (FID)

Symptom: Baseline (detector signal) is continually offset to the positive or the negative with no short
term drift up or down scale (see Figure 6-5). This is indicated on the output recorder.
Cause: Baseline offset problems in an FID 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. Contamination can enter through the burner air, burner fuel, or carrier. Secondary sources are
contaminated air, fuel, carrier lines, or regulators.
a. Hydrocarbon contaminates in carrier gas, hydrogen fuel or air can cause the FID to produce
an output signal as they are burned.
2000-OSM, F1
NORMAL
Figure 6-4. BASELINE NOISE
BASELINE
TIME
NORMAL
Figure 6-5. BASELINE OFFSET
NOISE
AMOUNT OF
OFFSET
BASELINE
TIME
OFFSET
6-3