Re: Looking for ways to measure AC line voltage with a uP.


Donald wrote:
Tim Wescott wrote:

Donald wrote:

Looking for ways to measure AC line voltage with a uP.

The uP would connect to a PC serial port.

Also measuring AC line current would be useful.

thank you

donald


There has to be a bazzilion. How accurate do you need to be? Low cost?
Size? Weight?

One basic method would be to get a reduced-size version of the waveform,
then either rectify it and sample it with an ADC, run it through a true
RMS chip and sample it with an ADC, or sample it fast enough with an ADC
that you can calculate RMS (or whatever) in the microprocessor.

Another would be to rectify the high-level voltage, then drop the
resulting DC voltage down and measure it.

You'll need to be isolated, so you either need to have the
microprocessor running on the "hot" side and isolate it's communications
from the PC, or you need to isolate the AC while getting an accurate
copy. The former technique would call for opto- or other isolators
between the microprocessor and the PC, it would make it easy to get an
accurate measurement, but it would make it harder to work on the
circuit. The latter technique would keep working on the circuit easy,
but would make accuracy expensive.


Thanks Tim,

I would like to measure the AC line on a remote heater and water pump.

I can run a RS-485 to the site, but measuring the AC side is where I am
having to be creative.

My idea is to isolate the line measuring side from the uP.

LEM make modules useful for that. Hookup measured voltage on one side
get an isolated signal out the other. They do need +/-15V.

http://www.lemusa.com/category/13.html

They are known primarily for their current sensors though.

Robert

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Relevant Pages

  • Re: Looking for ways to measure AC line voltage with a uP.
    ... Donald wrote: ... Also measuring AC line current would be useful. ... One basic method would be to get a reduced-size version of the waveform, then either rectify it and sample it with an ADC, run it through a true RMS chip and sample it with an ADC, or sample it fast enough with an ADC that you can calculate RMS in the microprocessor. ... You'll need to be isolated, so you either need to have the microprocessor running on the "hot" side and isolate it's communications from the PC, or you need to isolate the AC while getting an accurate copy. ...
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