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HMI: Measurements/Gas
Note: when there are not enough data points recorded to date to calculate the short or
long-term trend, then the corresponding "stack not enough" alarm flag is set. The value is
not displayed in the HMI and is replaced by a "-" instead.
The time horizons need to be defined first:
• The "short-term" time horizon can be set from 20 min to 1,200 minutes (20 hours)
720 minutes (12 hours) is a good default choice
• The "long-term" time horizon can be set from 20 days to 200 days
30 days is a good default choice
These horizons will set the warning time that you will get before the relevant gas pressure
threshold level is reached. The longer the horizon and the more accurate forecasted value
but also, remember, the longer it will take to fill the stacks!
HMI: Settings/Gas monitoring
For "long-term" gas pressure trend calculations, the equivalent gas pressure at 20°C is
recorded every night at 2 AM. This allows for consistent conditions and the removal of
external influences such as variations in line load or solar radiation.
For the "short-term" trend, the recordings are taken much more frequently and will show
greater sensitivity to external influences. It is therefore much more difficult to calculate an
accurate leakage rate by using a standard calculation.
When 3 independent gas volumes are monitored, by assuming that the leak will appear on
only one volume first, a reliable detection of relatively rapid leaks is carried out by
comparing the measured extrapolated pressures of the three volumes taken two by two.
Two alarms can be set on the extrapolated gas pressure values calculated. They rely on the
time horizon set:
• The "long-term" alarm is raised if the long-term extrapolated gas pressure at 20
calculated to drop below the gas threshold 1 (nearly too low) that has been set
➢ This means that the gas pressure/level will be below threshold 1 within the
long-term horizon that has been set
MA-037 - CB Watch 3 Operating Manual
Figure 74 – Forecasted gas pressure values
Figure 75 – Time horizons setup
v7.0 - May 2020
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