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Model 360E Instruction Manual TROUBLESHOOTING & REPAIR PROCEDURES
11.3.2. Non-Repeatable Zero and Span
As stated earlier, leaks both in the M360E and in the external system are a common source of unstable and non-
repeatable readings.
5. Check for leaks in the pneumatic systems as described in Section 9.3.3. Don’t forget to consider
pneumatic components in the gas delivery system outside the M360E. 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.
6. Once the instrument passes a leak check, do a flow check (See Section 9.3.4) to make sure adequate
sample is being delivered to the sensor assembly.
7. A failing IR photo-detector may be at fault. Check the CO2 MEAS and CO2 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.
8. Confirm the sample pressure, wheel temperature, bench temperature, and sample flow readings are
correct and have steady readings.
9. 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
2
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.
10. If pressurized span gas is being used with a zero/span valve option, make sure that the venting is
adequate (See Section 3.1.2 and 5.4)
11. If it is the zero point that is non-repeatable, and if that non-repeatability seems to only occur at a certain
time of day, such as when worker occupancy is highest or lowest, make sure the flow of purge gas to
the GFC wheel housing has not stopped (See Sections 10.2.2 and 11.1.7 for more information).
11.3.3. Inability to Span – No SPAN Key
1. Confirm that the carbon dioxide span gas source is accurate; this can be done by switching between two
span-gas tanks. If the CO
2
concentration is different, there is a problem with one of the tanks.
2. Check for leaks in the pneumatic systems as described in Section 9.3.3.
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 RNG Menu (See Section 6.7).
4. Check to make sure that there is no ambient air or zero air leaking into span gas line.
11.3.4. 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
2
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 Section 9.3.3.
3. If the analyzer has had zero/span valve options 52 or 53, the CO
2
scrubber may need maintenance.
4. Check to make sure that there is no ambient air leaking into zero air line.
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