> From:         Richard.Prosser@POWERWARE.COM[SMTP:Richard.Prosser@POWERWARE.COM]
> Sent:         Wednesday, April 07, 2004 5:21 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [EE]: DC current measurement (100 A) with a transformer

> Warning - depending on your application, this type of sensor is only useful
> if you can tolerate the AC signal being injected onto the DC line being
> sensed. I spent a bit of time looking into similar methods but they all
> seemed likely to increase the AC noise level outside our spec. limits.
> On the other hand, for measuring a DC current in a less demanding
> application, they may be just what you want.
> NASA developed a similar system using special magnetics with a very square
> hysterisis loop. During the AC transistion an output voltage proportional
> to the DC current could be sensed. But it also injected noise.....

> Richard P



>>    There have been posts to this list in the past asking about measuring
>> large
>> DC currents without using a shunt resistor. The latest issue of Nuts &
>> Volts
>> magazine (April 2004) has an article on page 38 describing the construction
>> of a transformer based DC current meter with full scale up to 100 amps (and
>> no, this is not an April Fool's joke).
>>   The sensor is a toroid wound with 200 turns which acts as one half of a
>> transformer. The other winding is a single wire passing through the center
>> of
>> the toroid, carrying the DC current to be measured. The main (first)
>> winding
>> is placed inside the feedback loop of an oscillator made from a voltage

That point was mentioned in the article. The turns ratio does magnify
the switching current by enough to make it comparable to the measured
current.

John Power

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