Applies To:
  • CitectSCADA

The trend page intermittently does a screen regeneration at approximately 2 second intervals (i.e. blank 2 second, redraw 2 second - blank). This is cleared by paging to another page and back again a number of times. Sometimes it takes 1 or 2 times, other times it will take 10 or more times to get rid of it. 

The trend page may regenerate itself under high loading conditions. This usually occurs on a computer with slow graphic display or if the trending rate is high with a large number of samples.

Citect tries to optimise the display of the trend. It is sometimes faster to redraw the entire trend than scroll it a few samples. Citect will do this when the display of the trend is 3 samples behind the acquisition of data. For example, while drawing a trend, 3 new samples arrive. It is normally quicker to delete the entire trend and redraw it than scroll it 3 times. However, it is possible that even redrawing the trend will take the same time as 3 new samples. If this happens then Citect may continuously re-draw the trend.

To solve the problem you should try to speed up the display of the trend, increase the sample period or increase the parameter [Trend] MaxScroll. You can speed up the display of the trend by reducing the number of samples displayed on the screen, reducing the size of the trend, using a faster computer or graphics card, or by adding more memory to the computer (if memory is low). Increase the sample period by changing the configuration (eg from 1 to 2 seconds). Increase the parameter [Trend] MaxScroll, this parameter tells Citect how may new samples arrive before it will refresh the entire trend page, the default is 3 - try increasing to 5.