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Autor
Maximum power measurement is mentioned in literature but what the lowest power which shelly 2 pm can measure?
I have noticed reading of 1.4w but does it measure even lower? 
What is the range of shelly 2pm power measurement?
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- SHELLY PLUS 2PM
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Raptor22 -
9. Juli 2025 um 18:41
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Because it can measure at least 10A * 230V = 2300W and I assume there is at best a 12bit ADC used the lowest possible ADC quantization is:
- 10A/2^12 * 230V = 0,56W if only positive values are possible
- 10A/2^(12-1) * 230V = 1,12W if positive+negative values are possible
The bigger "problem" is the ADC accuracy which can be as bad as several LSB's depending on gain/offset-correction, temperature drift, aging affects, ... -
Energy and power measurements in Shelly plus 2PM is executed by an ADE7953 energy meter chip. The analog/digital conversion in this integrated circuit is done with a 24 bit resolution. Thus, the measurement range is wider than above mentioned.
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24 but resolution
OK, they use a SigmaDelta modulator for converting the analogue values. So the "24 bit resolution" is achieved by a crazy high digital downsampling factor. So it is digitally possible to generate a "calculated" resolution of 24bit (but with systematic noise).
But for the external and internal analogue hardware it will probably not be possible to be accurate above 14/16bit without EXTRAORDINARY efforts.
So even if they claim a "resolution of 24bit" the accuracy would probably be more in the range of a 14bit ADC.
It would be interesting if Shelly would include this information in the datasheet.
I don't know if the Shelly EM Mini Gen4 uses the same modulator, but for this device the datasheet claims a "Voltmeter accuracy" and "Ammeter accuracy" of +-1%
