Teledyne GFC-7001T - Trace CO Analyzer - Manual (Page 267)

Troubleshooting and ServiceTeledyne API – Model T300/T300M CO Analyzer
Teledyne Analytical Instruments 267
12.3.2. NON-REPEATABLE ZERO AND SPAN
As stated earlier, leaks both in the GFC7001T/GFC7001TM 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 11.3.2. Don’t
forget to consider pneumatic components in the gas delivery system outside the
GFC7001T/GFC7001TM 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 11.3.3)
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.
12.3.3. INABILITY TO SPAN – NO SPAN BUTTON (CALS)
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 11.3.2.
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.
12.3.4. INABILITY TO ZERO – NO ZERO BUTTON (CALZ)
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 11.3.2.
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.