6-4 2000-OSM, F1b. The gases may be pure, but contaminated tubing or hardware components in the analyzer orcylinder regulator(s) contaminate the makeup gases as they pass through them. The FIDdetects theses contaminants, resulting in a noisy baseline.c. An FID is generally equipped with a catalytic air cleanup unit to remove hydrocarbonimpurities from the burner air. If the air cleanup unit fails, the impurities in the burner air canappear as detector noise.4. A continuous presence of sample at the detector due to sample valve leakage. Perform TestProcedure 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).NORMAL NOISEFigure 6-6. BASELINE RANDOM NOISECause: 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 faultyelectrical connections.a. Electrical noise from the FID amplifier could result from a noisy power supply or defectivecomponent 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 cableconnects the detector and the FID amplifier. Defective coaxial cables or poor electricalconnections are often sources of noise.2. Contamination can enter through the burner air, burner fuel, or carrier. Secondary sources arecontaminated air, fuel, carrier lines, or regulators.a. Hydrocarbon contaminates in carrier gas, hydrogen fuel or air can cause the FID to producean output signal as they are burned.b. The gases may be pure, but contaminated tubing or hardware components in the analyzer orcylinder regulator(s) contaminate the makeup gases as they pass through them. The FIDdetects theses contaminants, resulting in a noisy baseline.c. An FID is generally equipped with a catalytic air cleanup unit to remove hydrocarbonimpurities from the burner air. If the air cleanup unit fails, the impurities in the burner air canappear as detector noise.d. If water accumulates in the FID vent, the detector effluent flow can bubble through theaccumulated water. This in effect back-pressures the FID, causing the flame intensity tofluctuate. This can appear as a noisy baseline as well.
