> Hi all,
> this is probably something silly i'm overlooking btu I have a custom built
> optical sensor. When I measure across it with an oscilloscope, I get a
> range
> from 0 to 5V.  If I then hook it up to a Ni DAQ card, the computer always
> reads it as high... measuring in parallel the range is now only 2 V to 5
> V... any idea why it's unable to drive to ground now? thanks a lot
> Ben

I wonder what the input of the DAQ card looks like. It may have a negative
bias current that causes a positive input voltage when driven by a high
resistance. Does the DAQ read zero if the input is open circuited?
Depending on what you're driving this with, you may be able to add a
pull-down resistor to fix the problem.

Harold


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