Table 6-4: Evolution of the Gas Daily Trend
Note the following points:
• If the Hydran M2-X undergoes a power failure that lasts less than 1/6 of
the trend period, the corresponding trend reading remains unchanged
when the Hydran M2-X is powered up again.
• If the power failure lasts more than 1/6 of the trend period, the
corresponding trend reading is reset to 0.0 ppm/period.
• If the user changes the hourly or daily trend period, the corresponding
trend reading is reset to 0.0 ppm/period.
6.2.5.3 Guidelines for the Periods of Gas Trends
Here are a few guidelines on how to set the hourly and daily trend periods:
• The hourly trend period should be long enough to filter out reading
fluctuations caused by short-term changes in ambient conditions and
transformer operation. The factory default of 24 hours is a good starting
value.
• The longer the trend period, the higher the trend value in ppm will be for a
given steady increase in gas level reading. For example, a constant gas
level increase of 10 ppm/24 hours will result in a 10 ppm/period reading if
the period is set to 24 hours, but in a 20 ppm/period reading if the period
is set to 48 hours.
• The longer the period, the smoother the trend readings will be. However,
it will take longer for the trend to stabilize (“taper off ”) to its final value. In
the preceding example, it would take two days to obtain the final value of
10 ppm/24 hours; in the second case, it would take four days to reach the
final value of 20 ppm/48 hours.
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