Applies To:
  • CitectSCADA 5.31, 5.40, 5.41, 5.42, 5.50, 6.0, 6.1, 7.0
  • CitectHMI 5.31, 5.40, 5.41, 5.42, 5.50, 6.0, 6.1, 7.0
  • CitectFacilities 5.31, 5.40, 5.41, 5.42, 5.50, 6.0, 6.1, 7.0
  • CitectSCADA Batch 5.31, 5.40, 5.41, 5.42, 5.50, 6.0, 6.1, 7.0
  • CitectSCADA Pocket 5.31, 5.40, 5.41, 5.42, 5.50, 6.0, 6.1, 7.0
Summary:

When using the process analyst, the user sets the time span to 5 mins for a particular time. In the Object View, we select maximum to display this at the bottom of the screen. When selecting a longer time span, with the same maximum, the value shown is not accurate. The reason is that for larger time spans, the data gets compacted: a set of points will be shown on the graph as one point. From the help: Maximum - causes the maximum value from cache to be returned. Note that this value might not be a real logged sample if the sample found is a multiple calculated sample. Also: Data compaction is the visual grouping of multiple data points into a single data point when the data in the archive is too dense to be displayed as individual data points for the selected time span.

 

Solution:

You can fix this problem using the Request Mode. This can be used to show one of the maximum, minimum or average for each calculated point. The normal mode is to average the raw points. If the customer wants to see the accurate maximum;
- click the Show Properties button.
- select the desired pen then
- select the Connection tab, under Request Mode , select Maximum
Then the value will be the maximum value out of all the individual samples within the multiple sample.
You can repeat the steps above and select Minimum.
For more see: Process Analyst for Operators > Understanding Process Analyst Pens > Pens: An Overview > Data Compaction

So that the customer can be sure of what he is looking at, in the process analyst, select the Show Points button to see which points are being compacted. Single data points will come up as ellipses, a point consisting of multiple samples are shown as squares, and interpolated points are shown as triangles.

There is a workaround: The old style trend pages / funtions like TrendGetTable() etc give you full control of the interpolation methods used. If you want to obtain a max or min value then you could also run a report to calculate it.

Also if you wanted this information in a column of the process analyst legend (it could be quite inefficient and complicated to acheive) you could make a custom column and use cicode to do a trendgettable on the period and find the maximum that way. See process analyst help file: Process Analyst for Users\Cicode Programming Reference\Implementing a custom column.

 
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