MM-IM User Guide
12
Historic Data
The MM-IM will store (trend) points in its memory, providing a history of the site which
can be read out remotely by Master Control.
Any real or derived analogue input or pulse counter point may be trended. For analogue
values, the firmware supports trending of:
■ Current values: the point value at the time the data is written to memory.
■ Average values: the average value calculated over the last trend interval.
■ Maximum values: the maximum value measured over the last trend interval.
■ Minimum values: the minimum value measured over the last trend interval.
For a pulse counter point, only current value trending is supported. The data recorded is
the instantaneous value at the end of the trending period.
The average, minimum and maximum statistical trend types are derived from a sample of
all of the valid readings taken within the trend interval. Thus if the inputs were being
scanned and updated once per second the statistical data (average, minimum or
maximum) for a 1 minute trend would be derived from the 60 samples taken within each
minute. The statistics would then be reset and recalculated for the next minute etc.
Points can be trended at any interval supported by Master Control in the range 1 to
65,535 minutes. A given point may be trended in any of the above types.
Configuration of trending is normally from Master Control and is automatic when the MM-
IM powers-up on contact with Master Control. Trending may also be configured from a PC
running MicroMC.
Trend streams on the MM-IM are identified by a unique combination of point derivation,
type, number, statistic and interval. When a trend stream is created, the message
configures the trend period along with alignment time and day. The alignment is used to
ensure that recording starts at a particular time.
The number of trend streams that an outstation can maintain is governed by the amount
of memory available for storing trend data, and the length of time that the data is retained
there. The trend memory is gradually filled up as time progresses. When the data is read
by Master Control the read data is deleted. The user can also view the data and/or delete
it using a PC running MicroMC. The MM-IM has 512 MB solid-state memory for local
storage of trend and alert data, equivalent to in excess of 10 million samples (for
example, approx. 1 year’s storage at a sampling rate of 30 analogue values per minute).
When the memory is 87.5% full or above, an alarm is raised to notify the operators.
A secure two-way protocol ensures that memory is released only when the trend and alert
data has been properly read out of the RTU. This helps to ensure that important alarm or
trend data will not be lost.
Alarms and Events
In addition to plant monitoring, the MM-IM can also be configured to raise or clear an
alarm or event should certain pre-defined conditions occur, either within the firmware (i.e.
configuration change) or within the monitored plant.
Alarms and events (collectively called alerts), are actually very similar to one another, and
differ only in the way the alert is handled once it has been detected. Events are time-
stamped and recorded by the MM-IM for later retrieval by Master Control at some point in
the future. Alarms are handled in exactly the same way as events but with one important
difference - the presence of one or more alarm records in the alert queue can be used to
initiate a call to the Data Gatherer using one or more pre-configured dial-back addresses
(IP addresses and/or telephone numbers) held in the configuration.
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