Measurement of generator voltage

[lurk]

I am trying to measure the output voltage of a 3 phase 1 KW asynchronous generator. The Data Acquisition card that I have to use only accepts a maximum of 10V and I was wondering if anybody knew of a good voltage transformer or circuit configuration to use. Specs on the max output we should be recieving are 120VAC max, 10A max. I was told to use a 12V plug in transformer but I'm not sure wether I'll be able to get a good signal out if the input voltage is less than desired such as only 60VAC any help or saftey precausions would be greatly appreciated.

 

[analogkid2digitalman]

Is the 120VAC stated an RMS or peak value? If RMS, the peak would be 1.414 x 120 = 170V. Thus may need more of a step down transformer so as not to exceed the 10V limit on the DAQ card. Is the DAQ card set up for 10 V bipolar (+/-10V) operation? This is needed for the negative portion of the sinewave. Will each phase need is own DAQ input? A transformer approach does provide isolation to the DAQ card from the generator, that is a good thing. There are also galvanic and optical isolation modules that provide attenuation available for even better isolation, do not know if any go that high in terms of input voltage.
If output is only 60V, you should still have a good acquisition, depending on the number of bits of resolution.

Hope this helps


Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[lurk]

Yes the 120V is stated at peak value and the Daq card is bipolar and I was thinking of giving each phase its own input. When you say if the output is only 60V I should get a good acquisition does that mean the transform will respond linearly to any amount of input up to its rated maximum

 

[analogkid2digitalman]

I believe it should respond linearly, the DAQ card input impedance is fairly high thus creating a very light load on the transformer, the core will not saturate. You can verify integrity of the signal with an oscilloscope if you like. Step down transformers are cheap and readily available, give it a try. Remember to set the DAQ sampling rate at least 10x of the frequency (ie if VAC is at 60Hz, sample at least 600Hz per channel) for optimimum sample integrity. (2x minumum to satisfy Nyquist).

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[busbar]

Suggest a Triad F13X or F1X transformer.

 

[Skogsgurra]

Done that - or at least tried to. It turned out that the common wall wart transformer introduces some distortion. Especially at higher voltages.

The reason is that the core iron gets saturated and since the primary winding is rather high impedance, you will get noticeable third, fifth etc harmonics. You will also get a down-bending Vin/Vout curve at higher voltages. It may or may not be important for your application. Consider using a transformer that is designed to work in the linear region. You can still get away quite cheaply, just select a transformer with a rated voltage about twice the maximum input voltage.

For best results (and highest cost) buy specially designed voltage transformers. They have the accuracy specified.

 

[tinfoil]

look at

http://www.flex-core.com/Specials/over-stock-voltage-transducer-specials.htm