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Troubleshooting & Repair Model GFC7001E Carbon Dioxide Analyzer
Teledyne Analytical Instruments 284
13.3.2. NON-REPEATABLE ZERO AND SPAN
As stated earlier, leaks both in the GFC 7001E/EM and in the external system are a common source of unstable
and non-repeatable readings.
1. Check for leaks in the pneumatic systems as described in Section 12.3.3. Don’t forget to consider
pneumatic components in the gas delivery system outside the GFC 7001E/EM such as:
A change in zero air source such as ambient air leaking into zero air line, or;
A change in the span gas concentration due to zero air or ambient air leaking into the span gas line.
2. Once the instrument passes a leak check, perform a flow check (see Section 12.3.4) to make sure
adequate sample is being delivered to the sensor assembly.
3. A failing IR photo-detector may be at fault. Check the CO MEAS and CO REF test functions via the
front panel display to make sure the signal levels are in the normal range (See Appendix A) and are
quiet.
4. Confirm the sample pressure, wheel temperature, bench temperature, and sample flow readings are
correct and have steady readings.
5. Disconnect the exhaust line from the optical bench near the rear of the instrument and plug this line into
the SAMPLE inlet creating a pneumatic loop. The CO concentration (either zero or span) now must be
constant. If readings become quiet, the problem is in the external pneumatics supplies for sample gas,
span gas or zero air.
6. If pressurized span gas is being used with a zero/span valve option, make sure that the venting is
adequate.
13.3.3. INABILITY TO SPAN – NO SPAN KEY
1. Confirm that the carbon monoxide span gas source is accurate; this can be done by switching between
two span-gas tanks. If the CO concentration is different, there is a problem with one of the tanks.
2. Check for leaks in the pneumatic systems as described in Section 12.3.3.
3. Make sure that the expected span gas concentration entered into the instrument during calibration is
the correct span gas concentration and not too different from expected span value. This can be viewed
via the CONC submenu of the Sample Displays.
4. Check to make sure that there is no ambient air or zero air leaking into span gas line.
13.3.4. INABILITY TO ZERO – NO ZERO KEY
1. Confirm that there is a good source of zero air. Dilute a tank of span gas with the same amount of zero
air from two different sources. If the CO Concentration of the two measurements is different, there is a
problem with one of the sources of zero air.
2. Check for leaks in the pneumatic systems as described in 12.3.3.
3. If the analyzer has had zero/span valve options, the CO scrubber may need maintenance.
4. Check to make sure that there is no ambient air leaking into zero air line.