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Isolate AC Supply for voltage Measurement

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Troin

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I need to measure AC supply voltage from two different sources , the condition is that I can't mix the Neutrals of these sources

I Can't use an isolation transformer since they are bulky, I am thinking of an optoisolator based solution which can give me pulse width proportional to voltage , Is it possible ? Can someone share an idea ?

With regards
 

karesz

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Hi,
I think that you can use an optoisolator, but in analog version...
Means, drive it with an serial resistor (dissipate power!!) or even an identical impedance capacitor(be care pls.with 250V AC capability!!), or a mx of both.
The LED current proportional outut current you can calibrate in AC/Linevoltage...
In all cases. its an analog solution; all inividual coupplers are to calibrate_current transfer ration are nonuniform & th serial capacitances have maybe +/-5% (or even +/-10%) tolerances...
Connect a revers polarised diode parallel with the LED for the AC modus.
K.
 

    Troin

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Troin

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Thank you for the speedy reply,will the led current transfer constant for the device life or will it need frequent calibration?


I am trying to use LM331 V/F converter to get frequency proportional to voltage, but it is not working yet , any ideas please ?

Deepak
 

karesz

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Hi Troin,
If you havent place/volumen for a small isolating transformer, than you will have place for a supply transformer for an U/F converter? Im surpryced! :)

K.

Added after 4 minutes:

No, of course isnt "the led current transfer constant", thess is exactly the defoult specification for a LEDs usability time.
especially, how much working hours are possible for (I think) 30% less output power...

Added after 2 minutes:

I think; the only one good design will be; if you have a 4-20mA current output sensor that is far powered at same time...
 

Troin

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The device runs on 24VDC which is supplied externally to many instruments in the system.
Since my project is a module I have to put all of it in a box of maximum din size 144x144mm
 

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