Mark,
I tried out both Pasco and Vernier's interfaces a few years ago. The
cables are the same, but Pasco's interface box included some built in
amplification, if you wanted to use it. In addition they put a resistor
between the input and ground that vernier didn't have. It was large (1 meg
or 10 meg) and
didn't effect most experiments, but we developed an RC lab where the probes
are set across the capacitor and the internal resistor greatly effects the
result. I now have my students, using the Vernier interface, measure
its input impedance. It makes a good exercise as there is a great deal of
digital noise in the data but it all averages out and they all get about the
same input impedance of 3 gigaohms.
My wife and daughter just returned last night from the southern part
of your country. They had a wonderful time.
Gary
Gary Karshner
St. Mary's University
San Antonio, Texas
KARSHNER@STMARYTX.EDU