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Input sample scale of HAE in CM40x

Question asked by Kelven.Mo Employee on Apr 10, 2014
Latest reply on Apr 11, 2014 by ColinJ

Hello, I read the hardware reference manual of CM40x, two questions comes up about the input sample scale of HAE.


Question 1: On Page1627: "Processing of two 24-bit signed input channels, consisting of one voltage and one current. The input full scale is limited to ~ +/-6,000,000"


The output of CM40x internal ADC is 16-bit unsigned integer, and the output of SINC filter is 16-bit signed integer. depends on the discription on page1637 in the hardware manual:


"A significantly lower full scale limits the dynamic range accuracy of the measurements. For example, a full scale, which is 50% lower than the  assumed 6,000,000 full scale, has the dynamic range reduced by 50%".


So either use ADC or SINC filter output as the input of HAE, which means the input scale is only 1% (65,535/6,000,000), right? why the CM40x reduces the dynamic range by itself?


Question 2: On page1640: The HAE harmonic calculations are specified for line frequencies between 45 Hz and 66 Hz. The voltage channel is used as time base and must have an amplitude greater than 20% of full scale.


Accroding to this discription, how should I use the output of the CM40x internal ADC as the input of HAE? the amplitude only has 1% of full scale (65535 vs. 6,000,000).


Thanks a lot.


Best Regards