Applies To:
  • CitectSCADA x.x

I have setup my trend files to keep six files with one months data in each file. Sometimes it seems that there is not quite six months history kept, what is the reason for this?

In the scenario above the maximum history will be six months and the minimum will be five months. Following is a simple explanation of how the trend history system works. Again using the scenario above, six data files plus one index file (.HST) will be created for each of the trend pens. As soon as a trend buffer fills up its data will be flushed to the corresponding .000 file. After one month the .000 file should be full with new data so the system will move on to the .001 file and so on until it has filled the .005 file. At this stage it will start back on the .000 file again, there will still be old data in the file but it will not be accessible. The only data accessible will be between the current time pointer and the beginning of the file. There is no provision to access the old data in the file, that is why the exact amount of history kept will change. The trend history system has been written to be as fast and efficient as possible.