I currently create daily filtered averages for many process parameters by having an AF attribute which creates a filtered version of the parameter (using an AF formula, and everything outside of limits =0), followed by a daily analysis which creates a daily average of this filtered value when it is >0. I would also like to create a daily standard deviation using the same filtered value, however, because the attribute used in the standard deviation formula has to be an AF attribute, I cannot figure out a way to remove these zero value from the analysis. on days where the parameters are outside of these limits, I end up with a large standard deviation as the filtered values contains several 0 values.

Is there anyway to filter properly for data going into a standard deviation analysis?

Hi Vasanth,

The method you described above did not work for this case, but, I did figure out a way around it. With the filtered expressions, instead of setting a filtered value to zero, I set the value to 'BAD', which seems to be similar to the 'nooutput()' expression in analyses. Then in the analysis, I can simply do StDev('Attribute1','*','*-1d').

The formula is something along these lines

A=Power;B=|Power|Min;C=|Power|Max;D=SAG Mill Feed Rate Filter;[if (A>B and A<C and D>100) then A else BAD]