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ACM 150
Figure 65. View valve cycles
ZPD trends
The ZPD Trends indicate changes in the FTIR detector signal, which is the relative
intensity of the infrared radiation on the detector (refer to
a complete explanation).
Background ZPD trend
The graph in
Figure 66
trend for the 'Background', which occurs every 2 hours. Because the background
gas (nitrogen) is consistent, the graph should be relatively flat.
Between service intervals, the trend is usually in the direction of a decreasing ZPD. A
decreasing ZPD is an upward trend on the graph, because ZPD is a negative number.
Following a service, where the magnitude of the ZPD increases, or following an upset
condition, where the ZPD is reduced, you can expect a 'step-change' in the trend.
Sample point ZPD trends
You can also trend the average daily value of the ZPD for any active sample point.
Below the ZPD Trends graph (not shown in
one of these points if you want to graph its ZPD Trend.
is a daily average of the ZPD over a 15 day period. It is a
Figure
110
ZPD Value and Location
66) are sample points 1-40. Select
for
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