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ad7755 energy meter ic doubts

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raman00084

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while looking at the data sheet i am not clear that what ct should i must connect, are how much Milli volt / amp must be given to current sensing adc pin.


regards
kalyan
 

schmitt trigger

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The information is outlined in the pin function description:

Pin 5, 6 V1P, V1N Analog Inputs for Channel 1 (Current Channel). These inputs are fully differential voltage inputs with
a maximum differential signal level of ±470 mV for specified operation. Channel 1 also has a PGA and
the gain selections are outlined in Table I.


Thus, once that you select a current transformer, then you would calculate a burden resistor that would provide that voltage at its maximum secondary current output.

Please bear in mind that ±470 mV is peak to peak, not RMS values. For a sinewave, that would mean 470/1.414 = 330mV RMS.
However, to properly measure distorted waveforms, I would calculate with a crest factor between 2 or 3. Which means that the RMS value should be 235 or perhaps 157 mV RMS.
Of course, if you employ the internal PGA with a gain different from 1, then the voltage must be scaled accordingly.


Also...do you realize that this chip is obsolete?
 

raman00084

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thanks for the reply. for 1 amp current how much millivolt rms must be given to v1p.
 

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