There is request that I often have from my customers, which are working in plants that are batch based: they would like to have a trend showing many variables for a specific batch.
This really seems simple at first. However, the requirements are typically as follows:
- the trend must start at the batch start time and end at the batch end time (or * if the batch is running).
- The trend must use a different pen color for each variable.
- The trend must show time as "Time into batch".
If a regular Trend object is used, the trend start time and end time can be set (with VBA code) to the batch start and end time. Each variable can easily be shown in a different color. However, there is no way to have "time into batch" on the x-axis. In such a trend, "relative time" puts time 0 on the right hand side, whereas a real "time into batch" puts time 0 on the left hand side. That's a major difference. People typically want to see What happened 50 or 100 hours after the batch start, not 50 or 100 hours before the batch end...
If a Batch Trend is used, then having it start and end with the batch is standard. Showing time as "Time into batch" is also a standard feature. However, all the variables will be shown in the same color (the color is assigned to the whole batch, not to individual tags). Therefore, such a trend is almost impossible to use if there is more than 2 or 3 tags.
We have tried using an XY plot with a "time into batch" tag as the x-axis. This approach gave correct results on a proof of concept, but the performance dropped to an acceptable level when the trend was showing a large number of values. The low performance was due to the consant re-evaluation of the trend's statistics (such as correlation factor).
Has anyone used an Activex trend object other than the standard OSIsoft ones? Or developed a custom trend object? All ideas are welcome!