Measuring power and a few other bits in home Watch

jonh6
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Report Thread starter 10 years ago
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Hi

I'm looking into how power monitors work, both ones that appliances plug into and ones that clip onto live wire going into consumer unit. I have read a lot of stuff about this and am still a little unsure on best way of doing it. I am doing my 3rd year project on this so need to design my own system.

For measuring power at the consumer unit I was considering using a CT to detect current and just assume the voltage is at 230V ( i dont think this fluctuates for than 5%). Measuring only the current waveform would mean I couldnt get the power factor so my real power calculation would be inaccurate (the apparent power would be approximated too). I want to try to make it easy to install and I dont know of a way that I can measure voltage at this point without splicing into wiring which would require electricians to install. Anyone know of a way around this?

The other part i need to do is design some sort of individual appliance monitor. These exist as well but cant find any info on how they work. I guessing they measure the pd between the 2 live pins of the plug and use some sort of CT (much smaller though??) to measure current. With both these readings PF can be calculated etc. Anyone know if Im on the right track with this?

The final question is would feeding the signals measured in both situations into small digital ammeters/voltmeters (just IC packages) and have these connected to microproccessor be the best way to get actual values. These would be sampled at a particular rate (unsure of what reate would surfice). Could I take instantaneous measurements of both voltage and current waveform and produce an equivalent power waveform and integrate that to get average real power?
One other thing, as there is a high chance waveform want be sinusoidal will standard cos(phi) work for power factor?

If some/all of this doesnt make sense it may be i havent understood actually how ac supplys etc work.

Any advice would be much appreciated
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