Baseline Signal Random Noise (Fid) - ABB PGC2000 Operation And Service Manual

b. The gases may be pure, but contaminated tubing or hardware components in the analyzer or
cylinder regulator(s) contaminate the makeup gases as they pass through them. The FID
detects theses contaminants, resulting in a noisy baseline.
c. An FID is generally equipped with a catalytic air cleanup unit to remove hydrocarbon
impurities from the burner air. If the air cleanup unit fails, the impurities in the burner air can
appear as detector noise.
4. A continuous presence of sample at the detector due to sample valve leakage. Perform Test
Procedure 3 (Sample Valve Leaking/Column Flooding).
5. Electronics circuit failure. Replace FID Amplifier Assembly.

Baseline Signal Random Noise (FID)

Symptom: Baseline characterized by random noise and/or spikes (see Figure 6-6).
Cause: FID noise is generally the result of electrical noise or contamination.
1. Electrical noise is usually isolated to a defective FID amplifier, defective coaxial cable or faulty
electrical connections.
a. Electrical noise from the FID amplifier could result from a noisy power supply or defective
component of the PCB.
b. Loose electrical connections can cause electrical signals to be sporadic.
c. Since the FID amplifier input impedances are extremely high, low noise coaxial cable
connects the detector and the FID amplifier. Defective coaxial cables or poor electrical
connections are often sources of noise.
2. 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.
b. The gases may be pure, but contaminated tubing or hardware components in the analyzer or
cylinder regulator(s) contaminate the makeup gases as they pass through them. The FID
detects theses contaminants, resulting in a noisy baseline.
c. An FID is generally equipped with a catalytic air cleanup unit to remove hydrocarbon
impurities from the burner air. If the air cleanup unit fails, the impurities in the burner air can
appear as detector noise.
d. If water accumulates in the FID vent, the detector effluent flow can bubble through the
accumulated water. This in effect back-pressures the FID, causing the flame intensity to
fluctuate. This can appear as a noisy baseline as well.
6-4
NORMAL
Figure 6-6. BASELINE RANDOM NOISE
NOISE
2000-OSM, F1