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CONTENTS
15.3
Alarms
Every measured value can trigger 'alarms' when it is in a certain value interval; those alarms can be made periodic.
Alarms carry a 'level', which is an administratively assigned number; the range of these numbers is entirely up to
the user; it may be used in
conditions (e.g. 'value_alarm_level
>
2'); it's intended that alarm levels for
different values correspond to the associated severity/risk value so that the notification rules can be made generic
(and independent of concrete values).
Configuration of meter value alarms is done not on the notification page, but on the energy monitor page. You can
configure a meter value's alarms by clicking the
icon next to it. This will open the interval alert configuration
page for it.
Every measured value is a just a number, or 'none' for some meters on some devices which are detachable, so it
makes sense to say there's no value.
The real line of the possible values can be partitioned into intervals using threshold points: e.g. voltage can be
below 100V, between 100V and 140V or above 140V, so there are two points, 100V and 140V, splitting the real line
into 3 intervals. The idea is similar to
configuring sectors of a meter's visual appearance
100
140
Naive interval configuration
Each of the intervals can be assigned an alarm level, which can then be analyzed by notification server conditions
(you can also 'none' if you explicitly wish to send no events for that interval).
It is often desirable to keep some level of hysteresis between two adjacent intervals, so that there is some threshold
the value needs to cross before we consider that it has left one interval and entered a different one, to avoid needless
notifications. This is accomplished by further splitting the threshold points into the top and bottom values. If a value
increases and crosses the interval boundary, we only consider that it has switched intervals after it's above the
top value. Likewise, if a value decreases and crosses the interval boundary, we only consider that it has switched
intervals after it's below the bottom value. E.g. you could use 95V and 105V for the bottom and top values of the
100V threshold point in the previous examples for a 10V hysteresis.
95
105
135
145
Interval configuration with hysteresis
Each interval is characterized by its lower threshold point (with its bottom and top values), its alarm level and period.
The exception is the lowest interval which has no threshold point (but still has a level and a period). The "none"
value is considered so distinct from all regular values that no hysteresis is possible, so it is also characterized by a
level and a period only.
The above sample configuration might look like this:
DLI LPC9 User’s Guide: 1.7.24.0
Summary of Contents for LPC9
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