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General => Technical support => Topic started by: pstiles on November 17, 2006, 05:13:56 PM

Title: Moving average of 3 or 5 samples as your final result.
Post by: pstiles on November 17, 2006, 05:13:56 PM

Can someone show me how I can sample a ADC input, and average the reading, then write to a DM location?


Thanks,

Paul Stiles

Title: Re:Moving average of 3 or 5 samples as your final result.
Post by: support on November 17, 2006, 08:37:47 PM

The following example is a custom function  reads from ADC(1) and stores a 3 point moving average.

To prevent large initial error, you must fill up the 3 DM during 1st scan by calling this custom function 3 times.

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 The last 3 ADC data are stored in DM[101],DM[102] and DM[103]
' K is the index to keep track of the current ADC data

DM[101+K] = ADC(1)    ' data are captured in the DM controlled by K
K = (K+1) mod 3       ' K will vary from 0,1,2

A = (DM[101]+DM[102]+DM[103])/3  ' A is the moving average of last 3
                                 ' reading.
A = (A+2)/4*4            '  This line is optional, to eliminate unreal precision
                                  '  in the intermediate value due to
                                  '  averaging.  After this expr the
                                  '  result will be in increment of 4 only.

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Title: Re:Moving average of 3 or 5 samples as your final result.
Post by: pstiles on December 03, 2006, 04:13:37 PM

In the example below you state that I must call this custome function three times duriong the first scan. By doing this it reads the intial values into the DM, but does not update the value.

I have tried calling this in the first DM, plus in a second custom function, but I still can not get a steady value. The value from the temp sensor is rock steady.

Below is the code I am using in the custom function.


DM[101+K] = (168*(ADC(8)-261)/1376+32)
K = (K+1) mod 5
B=(DM[101]+DM[102]+DM[103]+DM[104]+DM[105]+DM[106])/5
B=(B+2)/4*4
DM[1]=B

Title: Re:Moving average of 3 or 5 samples as your final result.
Post by: support on December 04, 2006, 04:54:19 PM

The ADC input is subject to white noise due to the presence of digital switching signal in the system and typically the reading fluctuates between +/-3 LSB or +/- 12 when using ADC to read the analog input (due to 4x normalization). Moving average will help to even out the fluctuation. You should remove the B=(B+2)/4*4 statement since the reading in DM is already scaled.