Verification With External Challenges - Ametek 5920 UHP User Manual

Verification with External Challenges

Unlike previous AMETEK UHP moisture analyzers, the 5920 does not contain an
internal moisture standard. In AMETEK's line of QCM-based moisture analyzers,
the primary purpose of the internal moisture standard is to monitor the sen-
sor's response characteristics and to enable on-line compensation for sensitiv-
ity changes that occur over time. Compensating for changes in sensor perfor-
mance is an important feature in a process analyzer as the sensor can foul over
time from exposure to "dirty" process streams.
However, in UHP applications, the analyzers are only exposed to extremely
high purity gas streams. These will not foul or degrade the active surfaces of
the sensor. As such, the performance of the QCM sensor in UHP service should
remain relatively constant over time. Our experience with the 5900 has shown
these analyzers to be very stable, with sensors exhibiting only minor shifts in
response over time.
Figure 1-4 shows data recorded for recalibration of 5900 Series Analyzers. (Only
a small fraction of the 5900 analyzer population has been returned for factory
recalibration/maintenance; the data in Figure 1-4 correspond to these analyz-
ers.)
In Figure 1-4, the observed change in sensitivity, corresponding to a 20 PPBV
challenge, is plotted against time since the previous calibration. These data
contain a high degree of analyzer-to-analyzer scatter and only a minor correla-
tion with time.
Shift in Response of 5900 Analyzers at 20 PPBV
8
6
4
2
0
-2
-4
0 10
Figure 1-4.
5900-Series recalibration
data.
1-8 | 5920 UHP Moisture Analyzer
20 30
Time (Months)
40 50
PN 592047901 Rev YC
60