Re: Phase in AC Circuits

[Leigh Palmer <palmer@sfu.ca>]

> I hope some of you can help me.  I read somewhere, but immediately
> buried it in my "important" reprints pile, about how to put the voltage
> of both the inductor and capacitor on the same dual-trace oscilloscope
> in such a way as to show their phase difference.  If any of you can
> describe how to do this or perhaps refer me to a site that explains how
> to do this I would be grateful.

One would like to display the individual voltages in a series LCR
circuit individually, for example. A problem arises because most
oscilloscopes are single-ended - they display voltages with respect
to a common ground. I used to get around this problem by using a
four-trace plugin in an old Tektronix scope. Two of the signals can
be displayed by using a common ground for them and inverting one
output with respect to its input. The third signal used two preamps
(one inverted) on the two ends of the component, with the sum
signal displayed. The latter constituted a differential amplifier.

If you have a dual trace oscilloscope you can only display two
signals. Just hook them up with a common ground between the two
components and invert one output. Make sure that your ac driving
source (oscillator) is not using the same ground as your
oscilloscope. It is usually possible to float the output of an
oscillator if it is not already double ended. Use a transformer
if necessary.

Leigh