Expression tags solving very slowly

We have a customer project where we are noticing extremely slow solving of expression tags (like simple evaluation of a few bits to create an integer value taking 10 seconds). For instance, we look at the status of a bit with an OPC tag looking at data in a PLC, and we have an expression tag that looks at the value of that boolean OPC tag and does an “if” statement to provide a resulting tag value for that expression tag that is a string with either “Y” or “N”. We have other instances where we are using expression tags to create a integer number for the value of the expression tag using a “binEnc” based on the evaluation of several OPC tags bit values.

Any ideas???

how many expression tags and what is the scan class? I would think having only 10 tags vs 200000 expression tags would make a big difference in the answer.

With a lot of tags on the same scan class, you will eventually start getting delays as the scan class goes through the tags sequentially. Assigning those tags to a less “busy” scan class with a different scan rate will help.


Thank You for the advice, turns out it was the whole scan class thing and how being in a single scan call over-filled the thread. Have since broken up scan classes and performance is greatly improved. Thank You all! :smiley: