need help in acs712 hall effect current measurement

i am using acs 20a hall effect sensor it outputs 100mv / amp. i am using this to measure ac motor current, how to measure ac millivolt using 10bid adc my controller is pic18f4620. kindly tel me the measuring technique i am fed up i tried all the methods in google but i cannot get accurate results kindly help . complier used is ccs

your sensor gives Vcc/2 when I=0
and for +20A DC 100x20=> 2000 +Vcc/2
for -20A DC -(100x20)=> - 2000 +Vcc/2
if Vcc=+5V => output =2,5V +-2,0V at +-20Amps
With ADC 10 bits => delta max= 40 Amps for delta 4V
=> 1023*4/5= 819 points for 40 Amp peak to peak => 20 points / amp or resolution 1/20 Amps => +-50mA

We suppose , AC is sinusoidal ! (no distortion with hamonics)
if signal is clean,
you can take measures at 0.1 mS (or less) means 200 measure for one periode 50Hz,
to catch the maxima and minima value => peak to peak value
RMS is proportional .. and adjust your calibration coefficient to read Amps or xx.x amps

i did a similar measure but for voltage 230V AC.. use of a transfo 230V/9V and scale the signal around +2,5V DC.
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this methord works only for voltage and resistive loads in current. for inductive loads it is not working correctly because the output wave form is nor pure sine

Hi,

this methord works only for voltage and resistive loads in current. for inductive loads it is not working correctly because the output wave form is nor pure sine

Click to expand...

The method works for resistive, inductive, capacitive or any load inbetween...

But it does not work for "non linear" loads.
A not saturated inductor is linear --> it works (because the current is sinusoid)
A saturated inductor is not linear --> it doesn't work ( because the current is not sinusoid)

Klaus

I believe, the PIC processor is fast enough to perform true RMS calculation on the sampled current.

how cum the multi meter read correctly for all loads?

A multimeter is measuring either true rms or averaged rectified value.