Re: Current Transformers

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "James T by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jamest2000-at-att-dot-net>

Hi Terry, Gavin, Gary, all,
 Thanks fot the help. The link to Simpson just confirmed what I am doing.
 I guess I was just dreaming but I thought that there were meters with
rectifiers and stuff in
them to use with  shunts on AC. Oh well.


> A current transformer (CT) will be quite linear if the load impedance is
> below some specified value.

 Do you mean above? It is my understanding that most CT's want from 100 to
1000 ohms load across
the outputs to get a voltage output. I used a 2K rheostat to attempt to
scale to volts out
somewhat.
 I also tried to use a nice Triplet 5 amp panel meter directly across to
output. Did the same
using a digital meter. Also put the rheostat in series with both amp meters
to improve the
linearity. 0.5 ohms is a near dead short, isn't this basically what the amp
meter is, in this
case?
 Either way the output was not linear.
 I would like to avoid the op amp to keep things simple and not worry about
weird TC caused
problems.
 BTW all testing is being done with 1000 watt lamps for a nice clean load.
 I'll keep working, thanks guys.
 Regards,
 James T


> The output current will be exactly 5/60 of the
> input current if the load impedance is zero, but will be acceptable if the
> load impedance is below some value like 0.5 ohm.  Therefore, if you try to
> draw more than 2.5 V from the 5 A winding, you will start to see
> nonlinearity, even if the currents are within rating.