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Calculate Steady RMS value with AD7607 and Blackfin 504F


In my application i am trying to measure three phase current and voltage along with Neutral thus we are using 8 channel simultaneous sampling ADC... Currently i am collecting 128 samples over 2 periods of the input i.e. 40msec and then passing it through a bandpass filter and then doing a radix 4 fft , then i am calculating the mean of the output of  FFT  along with multiplication factor and displaying the result... I am not sure if this is the best way to achieve a stable reading of 2 cycle of input as more than 2 cycle cannot be afforded for measurement in my application


... I am not using a zero crossing detection i am just sampling at a fixed period of 40 msec using ACM and DMA for data collection and making sure of the sampling time.

Can anyone guide a better method as i am still seeing fluctuations of around 30mV .. as my experience in metering is zero...

In Anticipation


Sijeo Philip