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The current sensing across R65 will not include the solenoid back EMF current when the MOSFET is off. You may need either high side current sensing or high side switch.. I'd go for simplicity of a P-MOSFET with a discrete driver for this current range and frequency.
Can you scribe this "12V signal" source ? If it is normally configured to drive the primary side of a ignition coil pack then you might be in for a surprise, as 1000V back EMF spike normally exists on this wire during the spark gap discharge. It may not be so simple to use this a your signal...
If your talking about AC line frequency then something like the MCP3905 has a negative power detection logic output pin. I'd assume many other energy measurement ICs come with similar functionality.
Ok I finally got it, the voltage measurement is relatively spectral pure with a very high S/N ratio. The power meter then effectively becomes a product detector or synchronous demodulator. Low filtering the 'mixer' output limits the current channel bandwidth, increasing S/N ratio and achieving...
The problem is to calculate real power the instantaneous voltage and current must be multiplied and then averaged or low pass filtered.
Any inherent noise in the V or I samples will show up in the average power calculation.
The only way I can see to band limiting is put V and I samples through...
I am trying to understand the specs for energy meter ICs. Microchip, Cirrus and Analog Devices for example have utility meter ICs
that claim 1000:1 dynamic range at 0.1% error.
This means 1000W @ +-0.1W or 1W @+-0.001W
So does that really mean the meter can actually detect between 0.001W to...
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