Diablo 5000B, Getting Started Manual

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Troubleshooting
38 Diablo 5000B Real-Time Gas Analyzer Getting Started Manual
To confirm a leak in the RTGA interface, run an "Air and Water Check" as described in step
2 with the isolation valve *open* and the sample inlet plugged. At the bottom of the 597x Air
and Water Check report, the 28/69 Nitrogen% should be <10%. If the Nitrogen% is
significantly higher than 10% then you may have a leak in one of the fittings connected to
the RTGA interface.
4) To check for a plugged sample orifice, open one arm of the sample interface "Tee" to
ambient (room) air. If the interface pressure displayed on the PDR2000 is significantly below
80 mTorr (0.08 Torr), then your sample orifice may be plugged.
Addressing Signal Instability
The most common cause of signal instability for signals from the mass spectrometer is exposing the
detector continuously to very high levels of ion current. To monitor and address this we
recommend including the Total Ion Signal in your method.
This signal represents the total signal that the electron multiplier detector is generating across the
entire mass range (not just for the m/z values included in the method). For best detector stability
and lifetime, it is best to keep the total ion signal < 1,000,000 counts, with the best stability <
500,000 counts. By including this signal in the method you can monitor this important parameter in
real time.
If the Total Ion Signal generated by your method and sample is continuously greater than
approximately 1,000,000, you can take one of the following steps:
1) If large matrix/sample peaks like nitrogen in air are included in your scan range or as a SIM
ion, and you don’t need to monitor them, then you can sometimes change the scan range to
exclude those peaks. Alternatively, you can switch to SIM mode and exclude those m/z
values from the list of SIM ions.
2) Reduce the voltage applied to the electron multiplier until the total ion signal falls below
1,000,000. You make this adjustment in the “Advanced” window of the MSD instrument
settings:
Figure 26. The MSD Advanced Settings window showing a negative relative detector