A simple resistance capacitor circuit

[gar]

161031-1426 EDT

junkhound:

With the following actual circuit the experimental results are shown in the actual oscilloscope plot.

The circuit:
Tektronix CFG250 function generator.
Rigol DS2072A scope.
Mid 1970s Tektronix scope probe, 10X.

Series combination from common to voltage source (sig gen output) ---
-- 82 ohm carbon comp for current measurement.
-- 1.0 ufd Sprague 730P capacitor.
-- 10 k ohm carbon comp for current limiting for charging capacitor.
-- The nominal time constant is 0.010082 * 1.0 seconds.

The plotted capacitor voltage includes the 82 ohm voltage drop (1% error in voltage, but not waveform).

The voltage source rise time is around less than 50 nS. Scope waveform of the signal generator includes the signal generator, scope probe, and scope combination. No apparent oscillation with or without the series circuit being tested. Source impedance is speced at 50 ohms.

Plot:
Blue is voltage across both capacitor and 82 ohm resistance. Essentially the capacitor voltage drop.
Red is the 82 ohm voltage (capacitor current).

Note that 63% of 6 division is 3.78 divisions, and the plot is close to that at 10 milliseconds. When the scope time base is expanded it appears that 63% is at about 9.6 to 9.8 milliseconds.
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[Ingenieur]

161031-1121 EDT
Ingenieur:

Both mfd and ufd have been used for microfarad for a longtime. But I will admit that 1M for 1k would be confusing today for a 1000 ohm resistor, and I can see why you would be confused my mfd.

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that simplifies things

first case:
Vc = (1) (1 - e^-t)
I = (10^-6) (e^-t)
63% at 1 sec

second case:
Vc = (1/3) (1 - e^-3t)
I = (1/3 x 10^-6) (e^-3t)
63% at 1/3 sec

 

[junkhound]

161031-1426 EDT
junkhound:
With the following actual circuit the experimental results are shown in the actual oscilloscope plot
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So as not to confuse folks, absolutely no argument with your plot.
To avoid confusion, refer to the circuit diagram accompanying the plot in my previous post - there is NO 10k ohm, which does totally damp the oscillations.


The insert below is the circuit with gar's values (and tried to match the scales) which shows everything is the same, WHEN the circuit is the same .


Sorry if I confused anyone who is trying to learn, simply wanted to throw in a comment that everything is not as simple as the textbook examples.

edit: Whoops, after posting, see I did get the scale for the blue curve slightly different, same values though as gar's test.