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Re: [TCML] Measuring secondary current
On Sat, 1 Sep 2012, Antonio Carlos M. de Queiroz wrote:
A current transformer connected in this way produces an output mostly
porportional to the derivative of the current, not proportional to the
current, and with so many turns the transformer is probably full of parasitic
elements. Correct measurement can be obtained by using as load to the
transformer a series RC circuit, and measuring the voltage over the
capacitor, that adds an integration to compensate the derivative. The
connection has a band-pass characteristic that is flat over a large range of
frequencies, and can easily be calibrated as you did. Typical values are at
most tens of turns in the toroid, capacitor in the nF range, resistor in the
hundreds of ohms.
The values given seem strange. Too many turns in the toroid, too small
sensitivity, too high resonance frequency.
Thanks. I was actually going off a post to TCML ages ago which recommended
300 turns on the toroid, evidently for a different purpose!
Is there a reference for CT construction you can point me to? Certainly I
can follow your directions approximately (say, 25 turns on the toroid, a
100nF capacitor, 470 ohm resistor), but I would be doing so without
knowing how any of those values interact or affect the final measurement.
Antonio Carlos M. de Queiroz
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