Thread: DIY Data-Logger
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Old 07-22-09, 10:23 AM   #10
NiHaoMike
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The output must be integrated before rectification. I don't know exactly what circuit or algorithm to use since I have not used inductive current sensors for precise measurement. I prefer hall effect current sensors or shunts.

And yes, you need to integrate power as vectors (not to be confused with the integration used with inductive current sensors). Which basically means to measure the voltage and current at a sampling rate of at least a few kHz, multiply the pairs individually, then take the average of them. (Not exactly the mathematical definition of integral but close enough.)

One way to make a cheap wireless power sensor is to take a cheap stereo wireless audio transmitter and receiver (such as a pair of wireless headphones), then use a voltage divider and current shunt to supply input to the transmitter (use a small power supply to power the transmitter itself and possibly the instrumentation amplifier for the shunt). Then adjust the receiver volume for the optimum precision (should be just under the maximum signal range of your A/Ds in worst case), tape it in place to prevent accidental adjustment, and calibrate it.
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