Measuring AC Power Line

[sougata]

Hi there,

My problem is I need to make a circuit that senses the AC RMS voltage and takes certain decisions. Now Interfacing to the power line my way are:

1. Use a 20:1 transformer , make a potential divider, on the dc side to account for the diode loss, and do the adc. Tried - results non-linear ,unsatisfactory for the input range.

2. Use an IL300 or similar circuit to make a linear optoisolator - Increases overall price.

3. I am wondering can I use a PIC12F675 to sense the input AC and PWM an I/O to an opto-coupler or shift- out the values

Can you shed some light on the third option.

By the way my circuit would be used on a three phase line-to-line sensing scheme.

Regards

Sougata

[Luciano]

Hi!

Voltage-to-voltage signal conditioner:
http://www.ayainstruments.com/products3.html


Other solution:

The link below is the schematic of an uninterrupted power supply.
See the signal IN-RECT on the schematic page 1 (Top left corner).
See the same signal IN-RECT on the schematic page 2. (Top left corner).

http://www.eserviceinfo.com/download...400i_600i.html

Be careful with AC Mains voltage!

If you try it, let us know how it works.

Luciano

[sougata]

Hi Luciano,

Thanks for the post. I live in Kolkata India and would not be able to source the Aya products. Other design constraint are space and cost. Please let me know if you have any ideas. Whatever it is if I get through the problem rest assured that I will post the schematic and code.

Regards

Sougata

[sougata]

Hi everybody,

I am working on a routine with 12F675. Since the frequency of the ac line is quite predictable I am sensing the zero cross then starting the sample at almost the peak of the AC waveform. As you know that the average dc voltage is 0.707 times the ac RMS, so it is quite easy to sense it as long as it is sine wave. I am then shifting it out via an opto-coupler. By the way I am using a transformer less power supply (read non-isolated) for the 8 pin PIC.
Microchip has got an appnote on the same (PS).

Regards

Sougata

[jmgelba]

Are you trying to measure just one phase, or all phases, or the difference between one phase and another? Are you measuring power, volts, amps?
If you give me size and power constraints, I can probably come up with something since I used to design switch mode power supplies :-)

[sougata]

Hi jmgelba,

Thank you for your post. My application is basically a voltage monitor (via RS232) and trip circuit with presettable hysterisis and auto recovery. I would be measuring between R-Y and Y-B. It is the output of a DG and a three phase three wire system. Any idea or suggestions would be greatly appreciated. Thanks in advance.

Best Regards
Sougata