IAP Technique-Counting / Accumulating Digitals

If you want to know how to count a number or digitals or accumulate a digital this is the page for you.

Summary

UCN and AM regulatory processing blocks are able to read the status of a digital signal and input it to their algorithm using a 1 for the ON state and a 0 for the OFF state. Effectively the digital signals are converted to analog values.

After this conversion any processing that you do with normal analog signals can be performed. Most would be nonsense but if the algorithm is a counter or accumulator it can be a valuable technique.

Why use this technique ?

This technique is typically used where there is a need to count the number of digital signals in a particular state or to accumulate how long a digital has been in a particular state.

Typical applications are:

Adaptive Gain Control

Counting the number of secondary controllers in a primary / multiple secondary cascade strategy. The count being used to set the gain of the primary.

Excursion Counter

Counting the number of occasions that an analyser is in an alarm state over a given period of time.

Implementation

Implementation is very simple. Just configure a regulatory PV entity to pull in the digital signals as a conventional input connection.

So if you needed to count the number of controllers in cascade mode you would configure a regulatory PV entity with a summer algorithm then enter something like:

PVEUHI	3 (because 3 inputs)
PVEULO	0
NOPINPTS	3
PISRC(1)	FC101A.CASMODFL
PISRC(2)	FC101B.CASMODFL
PISRC(3)	FC101C.CASMODFL

Then the PV of the regulatory PV will be the number of controllers in cascade.

Alternatives

The only real alternative is a CL sequence. However much more applications effort would be required and extra configuration would be needed to implement alarms, ranging, trending etc. which are inbuilt to this solution.