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Searching for some precision mains power meter (0.1mA)

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Swainster:
I have a RS branded GWInstek bench power meter with 100nA resolution on the 5mA range. Some numbers just to get a feel for things:

With mains 115VAC/60Hz the current is about 0.06mA even with nothing plugged into the outlet. With a long IEC lead (still no load) then the current goes up by 0.012mA. With mains set to 240VAC/50Hz then this leakage current is about 0.1mA. Plugging in a few random bits of old test equipment (power supplies, electronic load) with hard on/off switches in the off position typically adds another 0.1mA (except for one which added 14mA... this I know has crispy RIFA caps inside so I guess it is trying to telling me something). A random cheap chinese phone charger uses about 2mA without any load, though to be fair this was dropping as the internal caps reformed.

I bought this power meter to measure standby/idle currents according to IEC62301, which is actually something typical power meters cannot do. One of the requirements is 1mW resolution - thats under 9uA at 115VAC. My suggestion is that if you are serious about this type of measurement then you will need a proper bench type instrument. If you are only interested in current then a DMM could be good enough, but if you actually want to know power/energy used then a power meter is the most practical solution (2 DMMs will not work without a lot of extra work to extract and sync the data, even assuming they have enough bandwidth).

TLDR What you want to do is non-trivial and probably the preserve of application specific bench instruments. Building a custom instrument to do it is always possible, but only practical for hobby/enthusiasts - In fact I think this kind of project would generate quite some interest on this forum. For commercial purposes it makes far more sense to just buy the proper tool for the job.

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