Date: Sun, 13 Nov 2005 19:35:23 -0600

Author: Stan Dodds

Subject: computerized AC circuits


Has anyone tried to do an AC circuits lab exercise with student-grade
data acquisition hardware? I'm having some troubles with the Vernier
LabPro system that seem to be inherent in the design:

1. The maximum real sampling rate is 10,000/second for one probe or
5,000/second with two probes (voltage and current). This limits the
practical frequency range to a kilohertz at best. Automatic fitting of
a sine wave gets flaky even sooner, about 300 Hz, so you have to
eyeball the parameters.

2. The samples are not taken at the same time, presumably because there
is only one sample and hold and one A/D. Understandable in low-cost
equipment, but the channel delay corresponds to a 10 degree phase shift
at 200 Hz. Not good when trying to show the 90 deg shift in a

Is there a work-around you use, or do you explain the quirks to
students without causing utter confusion?

Any help much appreciated.

From Sun Nov 13 22:37:50 2005