Re: pasco light probe oscillations

[Robert Morrison <morrison@pasco.com>]

Hi All,
This fluctuation can be the result of several different things. 
Some things to check are:

Improper Grounding:
Be sure that the computer and interface have a 
common ground, preferably earth ground

Beat frequencies
If you are experiencing beat frequencies you can
usually verify this by increasing the Sampling Rate 
to 2KHz and setting a stop condition of .5 sec.
At this rate, regular power related variations will be easily seen.

Unusually high noise
You may wish to look at a graph of the Input Voltage 
for the light sensor. Random noise of a few millivolts is 
common, but anything higher is unusual. Does the noise 
persist even if the light sensor aperture is completely covered?

Mark, if it is possible, please fax me a copy of your graph.
Thanks,
Robert  

At 02:30 PM 4/17/98 -0400, you wrote:
> Was the 12V bulb connected to a power supply of a battery?  If it was the
power
> supply, it could be the line frequency vs. sampling frequency thing (beats as
> said in posts by other members of the list).  Connect the bulb to a
battery and
> try again.  That should make it clear if the problem is your power source, or
> your interface box.
>
> Since you have a 700 series interface, you could also elect to power your
light
> source with the Pasco power amplifier.  If the problem is a mis-match of the
> time base of the Pasco 700 with the line source, then the observed effect
should
> disappear when both your source frequency and your sampling frequency are
coming
> from the same box.
>
> -- 
> Hans G. Ammitzboll		physics@mindless.com
> Drew University Physics Dept.
> Madison NJ 07940
> 		   "Grow up, not old.  Be childlike, not childish."
> 							-Me


Robert Morrison                 Technical Support
PASCO scientific              Phone: (800) 772-8700 Ext 237
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http://www.pasco.com        morrison@pasco.com