Count Number of Changes in String Tag value

Forum / Questions & Answers

patch_hyland
updated 3 days ago
4replies

We are doing a thruput improvement project and trying to find a way to calculate how many serialized units move thru our workcells. The most robust signal we have to track this with currently is a string tag for the serialID of each unit, but I'm having trouble figuring out how to use the built-in Calculation functions to determine this accurately.

I'm hoping to figure out something that behaves like NumberOfTransitions does for a Bool tag, but for a string tag.

We want to build a dashboard once we can figure this out, to track each workcell's thruput by hour and a rollup for the area.

Thanks in advance for any ideas.

- smason
- 16 hrs ago
- Reported - view
Hi ,

Would the Count aggregate work in this case? It simply counts the good raw values in an interval.
- patch_hyland
  
  16 hrs ago
  
  Reported - view
  Hi , we had tried the Count aggregate for this, but it seemed like if the same value was written for a different unit, the count aggregate did not consider that in its aggregation. To be fair I haven't read the detailed OPC Foundation document about the details of how this aggregate works.
- smason
  
  15 hrs ago
  
  Reported - view
  Based on my testing, the Count aggregate counts every raw value, even if they repeat. I did this against a string tag I have that updates every second. There are only 8 unique string values that repeat, but the aggregate returns 3600.
- patch_hyland
  
  15 hrs ago
  
  Reported - view
  Thanks , oh, that may be the source of our problem. We're trying to get a count of unique strings over a period, so per your example/test, we would want an aggregate that tells us '8' not '3600'