s7-300 analog 'rate of change'

Hi
I have a need to measure a scaled analog inputs 'rate of change' against time.
I was considering using a timed interupt block and using a 'holding register' to keep the value of the previous check, then simply subtracting the difference of the actual value and the holding register and dividing it by the interupts time interval.

Does anyone think it may be better to average these over say 5 interupts to get a more accurate figure?

I am measuring the 'flow' of a powder onto a belt sat on a 4-20mA loadcell and need to approximate Kg/Minute

cjd1965 said:

I was considering using a timed interupt block and using a 'holding register' to keep the value of the previous check, then simply subtracting the difference of the actual value and the holding register and dividing it by the interupts time interval.

Does anyone think it may be better to average these over say 5 interupts to get a more accurate figure?

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Hi there,
What you have said is way to go.Accuracy at a given time will increase if the sampling interval is small. So averaging out 5 interrupts wont give you the more accurate figure.