How to grab a peak value.. but not an outlier?

I have an analog flow signal that fluctuates with many peaks and valleys. Occasionally due to valve changes a peak value (or several) will be way outside the mean value and I need to ignore those. How do I capture a peak value that is not too far outside the average value?

Actual average value is not what I need, I need the peak within ~ 10% of the average over last 24 hours as its more reflective of real process conditions.

How can I do that filtering in a Logix PLC?

Does this peak detection need to occur in a rolling 24 hour period or is there a full rest as midnight, for example? That doesn't change the base logic. the rolling 24 hour thing just adds some additional checking and record keeping.

I assume that you already have an average that you are happy with. Since you define your window relative to the average you will need that.

You have already pretty well defined your requirements. A peak, by definition, is the highest detected value. So:

GRT(Input, Peak) MOV(Input, Peak)

However, you also don't want to consider values some percentage above the average. This would be:

CMP(Input < (Average*(1+(WindowPerc/100)))

Combine them to get:

GRT(Input, Peak) CMP(Input < (Average*(1+(WindowPerc/100))) MOV(Input, Peak)

Keith

Well now, that looks right, and quite simple. Reset the peak first thing in the morning and that should do it. I'll run that today and see how it behaves. Thanks.