----- Original Message -----
From: meredith lamb 
To: 
Sent: Sunday, May 27, 2001 4:21 PM
Subject: Re: Simple photoelectrics


> Is there really....any technical advantage to using two side by
> side photocells (misc variety in a differential bridge), as opposed
> to using just one alone?  I'd think one cell would be simplier
> mechanically but I'am not sure if it would react the same
> circuit wise or as well (?) as two cells.

To check the noise level, I turned up the gain on a feedback unit until
local noise was clearly visible on the oscilloscope.  Then I clamped the arm
and looked at the noise again.  Clamped, it was much lower, so I am
convinced that the noise level of the sensors is much lower than the
background.
I suggest the same check be made with any sensor system.

The drift should be less with a differential system also.  As has been
suggested by others,  the balanced system reduces drift from temperature,
power supply, light source aging, etc.  Checking
a group of small solar cells, I have found that they have nearly identical
characteristics.

George Harris

George Harris

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