Re: data search.. RL circuits examples

[Bob Muir <muirrob@hamlet.uncg.edu>]

On Thu, 25 Apr 1996, Paul Hutta wrote:

> I recommend using a DVM as a series resistor along with a 10 uF capacitor.
> This provides a time constant of about 100 seconds( assuming a meter
> resistance of 10 M Ohms).  The students can take the data with a stop watch.
> In fact if they plot a discharge curve, they can take the "ln" and estimate
> the actual resistance of the meter.
>
> This experiment works well with a wide range of students from engineering
> majors to technicians.  
>
>
> Paul Hutta  
> PENN STATE at Abington

DVM's are "sampling" devices.  The regularily "sample and hold" the 
voltage at the probe tips and then digitize the value.  This is why they 
do not immediately respond to changing voltages.  I recommend that people 
use an ANALOG voltmeter for such observations or an OSCILLOSCOPE.  These 
will work for time constants a few times greater than the observer's 
reaction times for starting and stopping a stop watch.  The oscilloscope 
will also show the whole voltage vs time curve!

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