K4SAV wrote:
> The thing that surprised me when looking at the designs others have done
> was that many people used the clamp-on ferrites that are intended for
> RFI suppression. These add a large series impedance into what you are
> trying to measure and will mess up the current you are trying to
> measure. What was needed was a small iron powder ferrite in a clip-on
> which will give low loss, but no one makes these in a clip-on (there is
> no application for these). I ended up splitting a toroid and
> fabricating a spring mechanism to make it function like a clip-on.
> Worked pretty good. I have two calibrated ranges on the meter and can
Tektronix sells various current probes, some AC coupled, some DC
coupled, some clip on and some where you have to pass a wire through
them. I own various models of these. They do not add any significance
impedance to the circuit. For example, the Tek CT-2 adds .04 ohms
to the circuit. You can easily make your own CT-2 or clip on version
by simply winding 25 turns on the core and terminating it with a 50
ohm resistor. Now it is true that if you don't use enough turns
or don't use a low enough termination resistance, then you will
introduce impedance into the circuit. In that case, using powdered
iron reduces the problem, but is not the real fix.
Rick N6RK
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