Re: [foxboro] Running Hours Counter and OSI-PI

Here's a snippet from the OSI-PI Server applications manual:

PI Totalizer Subsystem
The Totalizer Subsystem performs common calculations such as totals,
averages, minimum
and maximum values, and standard deviations. The output of a calculation
is stored in a PI
point.
The main difference between a Performance Equations point and a
Totalizer point is that
Performance Equations are based on Archive events, while Totalizer
results are based on
Snapshot events.
PI Totals are the most accurate way to represent production summary
data. Totalizers can be
started and reset based on time and event, and ensure the highest
accuracy in the calculation
of flow volumes and other critical variables used to monitor product
transfers or production
performance. Totalizer is especially practical for totaling measurements
or other process
variables at the end of specific time periods, such as the end-of-day
yields.=20

--------------------------------------------
Creation of a Totalizer Point
Totalization involves several steps, as follows:
1. Sample the value (RateSampleMode) from the input point called the
rate point
(SourceTag).
2. Possibly exclude the value based on a filter (Filter Expression).
3. Accumulate the observed values as needed for the specified summary
function
(Function and CalcMode).
4. Determine when the Totalizing period is complete and the accumulators
need to be
reset (TotalCloseMode).
5. Report the result (ReportMode).
---------------------------------------

Totalizer Input Values
Each Totalizer point has a single input called the source or rate point.
This is the point whose
values are summed, counted, or otherwise accumulated to produce the
required summary
value. The arrival of a new rate point value triggers the accumulation
and reporting functions
of each Totalizer point. Most often this process will be "naturally"
scheduled, that is every
new value reported to the system will be processed into the ongoing
accumulation.
Filtering
Each point may have one filter expression. This expression is evaluated
each time that a new
update value is received for each tag referenced in the expression. The
results are stored in
time order until the next rate point value is received.
Accumulation
The accumulation step takes the previous and current rate point values
into account when
adding to the accumulators. If a filter is specified, the stored filter
expression results are also
considered. The details of the accumulation depend on the specified
functions. The available
functions are: total, average, minimum, maximum, range, standard
deviation, count (of
digital states), and timer.
Accumulation Interval
The accumulation interval is the interval of time for which a
postprocessing calculation
occurs. Totals are often generated for intervals specified by a period
and an initial start time.
Alternatively, the interval may be defined by external events using a
trigger expression in PE
form.
Output
The output of the results is usually reported at the end of the
accumulation interval. The
output can also be estimated before the completion of the accumulation
interval. A running
result is also available.



Ken Moore
Celanese
Enoree Site
 
 
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