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Shorted top turn
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From: Gary Johnson [SMTP:gjohnson-at-ksu.edu]
Sent: Sunday, February 22, 1998 10:32 AM
To: Tesla List
Subject: Re: Shorted top turn
At 11:54 PM 2/20/98 -0600, you wrote:
>
>----------
>From: Richard Wayne Wall [SMTP:rwall-at-ix-dot-netcom-dot-com]
>Sent: Friday, February 20, 1998 1:45 AM
>To: Tesla List
>Subject: Re: Shorted top turn
>
>You wrote:
>
>snip
>
>>The measured inductance is 17.0 mH. I am driving the coil
>>with a function generator at about 30 volts. At resonance, current is
>>in phase with the voltage, so by simply measuring the voltage and
>>current, one can calculate the input impedance.
>
>Are you sure current and voltage are in phase? How do you calculate
>input impedance here?
>
>snip
>
>>Thanks,
>>Gary Johnson
>
>Very nice and well thought out experiment.
>
>RWW
I measure voltage and current at the output of the function generator (input
to the large coil) with a 50 MHz scope. Current is measured with a
high-frequency clamp-on current probe. Voltage at the toroid is measured
with a fiber optic sensor. That is also seen as a waveform at the scope.
Until this particular test the capacitive divider was between the top of the
toroid and a ground wire strung from the ground plane vertically several
feet away from the coil and then horizontally several feet above the toroid.
(That way, I would not 'see' the lower turns of the coil.) Maximum top
voltage is reached when the input current is in phase with the input
voltage. The input impedance is then simply the ratio of input voltage to
input current. In steady state, this ratio is in the range of 50 to 100 ohms.
GLJ