Measure AC Voltage

[ICD2]

Help how i can measure ac voltage with PIC (220V,380V)
How connect op. amp. and devide voltage.
Maybe someone have links.

[Guest]

I saw an application note on microchips web site for measuring 110VAC. maybe it can be adapted for higher voltages. Don't remember the ap note number though. You'll have to search through microchips web site.

good luck

[jds-pic]

use a flying capacitor -- think circus trapeeze. instead of writing how it's implemented i drew you a picture. note, use caution and the correct components when attaching to mains voltages. if you don't know what the correct components are then seek assistance from someone who does so you don't injure or kill yourself.

http://losdos.dyndns.org:8080/public/pic-uC/flying-cap-small.jpg

[SherpaDoug]

The flying capacitor is a neat idea, but not cost effective in most applications. That relay costs money, space, and power. It may be good for a home project or an expensive piece of exacting measuring equipment.

Instead look at using a voltage divider to get the signal small enough for ICs to handle easily, then use an instrumentation amp or a differential amp to shift the signal to the ground reference of the A/D.

Beware of safety when working with 380VAC, that is almost 540V peak! Many resistors can not handle that voltage safely even if the power is OK. A lot of breadboard techniques also become dangerous at these voltages.

If it is a home project and you don't need too much accuracy you might get away with a divider driving a "wall wart" transformer with an unregulated output. The transformer output will be roughly proportional to the input.

Sorry, no links at this hour Monday morning.

Be Safe,
Sherpa Doug

[jds-pic]

sherpadoug,

i agree with some of your points. however, the flying capacitor provides air-gap isolation, whereas a divider/instrumentation amp does not -- without additional cost and complexity (such as using a 1:N step-down line transformer). hence, as you alluded to, component selection is even more critical without an air gap.

based on the original post, i surmised that the poster had limited knowledge of the subject and only had to build one unit. so recurring bill-of-materials cost would not be a problem. and, safety is markedly improved with the air gap.

jds-pic

[SherpaDoug]

Analog devices (www.analog.com) has a new ad for their AD7400 isolated ADC that may be exactly what you are looking for. The price is $4 in qty 1000, but you might get a sample for free. At least the datasheet and App notes might give you some ideas.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[SherpaDoug]

[jds-pic]

[mvaraujo]

ICD2,

I will not go through the other points that the guys already mentioned, those concerns are true for a product.

In my company, I have a product that monitors AC line for disturbance and i have to measure voltage. The best solution until now is the use of a small transformer, in our case is 264V/13.2V. After the transformer I use OP07 amplifier in a differential configuration that goes to a full wave precision rectifier (also using OP07). In my case this is necessary because we really calculate true rms value of the voltage.

If you need only voltage value and would like to ignore ac voltage distortion, all you need to do this get the differential amplifier to some circuitry to get only the peak voltage and route this to the A/D. You can also use the full wave rectifier, sample voltage in fixed time using the A/D and look for the peak voltage inside the software. Lots of processing that perhaps can be easily solved outside the micro by some electronics.

Good luck finding out the best approach for your design!

Marcus

[ICD2]

So can anybody give me the link for (multimeters, Voltmeter)

[jds-pic]

[Mc]

LOL