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5890 TCD Troubleshooting
When trouble shooting the TCD, as in any detector. You should begin with half-splitting the detector from
the column and the inlet. This will ensure that you are looking in the correct place for the problem.
The first things to look/listen for:
1.
Is there an audible ticking sound coming from the switching valve?
2. Check flows -- setting column flow rate depends on the column installed and inlet used)
Capillary--- Reference flow should be approximately 3 times that of the column +make-up
Packed --- Reference flow should be approximately 1.5 times that of the column flow.
3.
Measure the resistance of the filament it should be 10 ohms (cold) and 11-13 ohms (hot).
Low Sensitivity: Possible causes
A. High/Low Gain Switch in the wrong position
B. Carrier Gas: (If the gas cylinder has recently been Changed) try a new tank
If a new method is being developed it could be carrier gas selection. Choose a
More conductive gas.
C. Filament resistance: measure the resistance of the filament it should be 10 ohms (cold) and
11-13 ohms (hot). Even though the filament reads correct resistance, it could be oxidized.
This could be caused by a leak in the system.
D. Flows- Either too high or too low
E. Contamination: Causing the detector signal to be elevated. This can be corrected by thermal
bake out of detector.
F. Filaments are oxidized: The only thing that can be done is replacing the detector assy.
Large Noise Spikes: Possible causes
A. Switching valve connections: O-rings can dry out and leak.
B. Manifold Block Needle Valves: excess grease
C. Leaks: From column fittings, make-up gas adapter, gas line fittings
D. Data System: cable connections
E. Switching valve: valve is defective
Other causes that have been found
F. In some cases Walkie-Talkie radios have been found to cause spikes
G. Power problems: poorly grounded power receptacles or power panels
Large Noisy Baseline: Possible causes
A. Filament Delta prt sensor: this sensor if defective will cause the electronics
To not function properly.
B. Electronic Detector Board: faulty
C. He/N2 Switch: is in the wrong position
D. Filament leads have a poor connection to detector electronics board
E. Contaminated gases
Low offset: Possible causes
A. Also see Symptoms of Low Sensitivity
B. Filament Continuity
C. Switching Valve malfunction
D. Gas flows are incorrect
F. Leak on the detector column connections
Large Offset: Possible causes
A. Column Bleed
B. Contamination
C. Switching Valve malfunction
D. Gas flows are incorrect
.
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