I have to agree with Andrew about the waveform which looks a lot like
transformer magnetizing current.
The thing is that you want the load on the secondary of the CT to be low as
it will reflect to the primary.
Ct's should , ideally be at the minimum load resistance for which you have
a reasonable voltage for your sensor. 1K seems high
Do you have any information with regard to the turns ratio?
What is the voltage across the 100W lamp with the CT and scope vs without
the CT and scope?
In other words, does the addition of the CT with its load have any
appreciable effect on the lamp load/
Don Kelly
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Beware that a current transformer must never be allowed to have an
open circuit secondary - that can result in some nasty unsafe voltages.
I can't see any load resistor on the current transformer secondary
in your setup. If you are really measuring the *voltage* output of
a *current* transformer into a high impedance scope, it isn't
giving you a useful representation of the actual current waveform,
and indeed the current waveform for the 100W lamp looks wrong.
You need to have a relatively low load resistance across the CT
secondary, and then measure the current through it by measuring the
voltage across it. The value of the resistor depends on the CT turns
ratio, CT power rating, and the max current on the primary side.
My bad, I didn't talk about the resistor. The packaged unit I came up
(device picture) with has a 1k resistor potted in there. That will
screw into a 3/4" knockout in a regular US electric box. That was big
enough to provide a load without actually crushing the output. It
dropped about half with 100 ohms.
If you are sensing with an OP amp it really would not matter that much
since they are pretty easy to drive into saturation.
I am using LM324s
