For this type of alarm to be valid, the parameter of interest must pass
through both thresholds within the specified time period. If the parameter
is between the thresholds when the alarm is set, or above the higher
threshold for an upward trend alarm or below the lower threshold for a
downward trend alarm, the alarm will not become active. Please note
that frequent communication with the data logger will cause the timing
function of this alarm type to run long.
For guidance on how to use this alarm, it may be best to consult
historical weather data from WeatherLink plot data (or other sources) to
determine what kind of behavior a parameter exhibits before
approaching a value of concern. Make note of how quickly the value
changes over time before it reaches that value. These changes will
govern your threshold values and time period. Your second threshold
probably should not match this value, but rather be lower than this value
for a upward trend alarm and higher than this value for a downward trend
alarm.
•
= (
Equal) This can be used to check whether any value is exactly equal
to the set threshold value.
•
Minus
or “Difference” alarm allows you to compare the difference
between two like variables. For this check type, the two variables must
be measured in the same units of measure in order to be compared. If
this check type is selected, the software will use the parameter pick list
on the row below for the second of the two like variables to indicate.
Enter a positive difference you want to compare in the available edit box
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