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Measure 0-500V AC using a Microcontroller

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Gursahib Singh

Newbie level 5
Sep 11, 2015
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Hi guys,

I need to measure 0-500 V(RMS) AC using PIC Microcontroller. Is there any way out or any circuit so that i am able to use AD736 RMS to DC Converter?

Thanks in Advance

Safety first! I would recommend a step-down transformer. Almost any secondary voltage will do, as the final scaling ratio can be achieved with a resistive divider.

Use rectifier circuit and convert it to DC and then do measuring. This will be the safest and reliable method to proceed over.


Some important questions:
* are you experienced to work with dangerous high voltage?
* is it a hobby project or a professional for mass production?
* do you need isolation?

The dangerous, but simple and most precise solution is a resistive divider, adding offset, ADC. Choose a sampling frequency of integer multiple of mains frequency (at least 16), and do all the RMS math inside.

The safe way is with a transformer. If you need phase information to a current, then you will see, that especially low wattage transformers introduce voltage phase shift from input to output.

Isolation is required on based on the application right?

If for your application circuit isolation is not an issue ( what I doubt when it comes to 500Vac ! ) a cheap transformeless measurement by resistive divider could be made, but it is absolutelly not recommended for safety reasons, as mentioned above.

If you are measuring AC mains (440V?), then without isolation you have to measure L-E, while the plant gets L and N. If you use the mains N as your common, then unless everything around your electronics is insulated and isolated from earth, sooner or later someone will earth the common line and cause all sorts of problems, smoke from the earth conductor, blown RCDs. . .

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