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ULTRASONIC MOTION DETECTORS -Reply



Could it be that you are getting reflections off of the ceiling and
floor when it is not dampened at floor level? You might try some
absorbant material near the ceiling just to verify this if you care to.
Gordon Shepherd
Guilford Tech. Comm. Coll.
Jamestown, NC 27282

LUDWIK KOWALSKI <KOWALSKIL@alpha.montclair.edu>
12/05/97 07:46am >>>
The air resistance data will be posted shortly.

We discovered a very strange behavior of motion detectors.
Facing our
linoleum floor, and collecting data at the rate of 10 samples per
second,
the distance to the floor (3 m) was correctly measured. But it was
not
correct at higher collection rates (for example 2 m instead of 3 at
20
samples per second). We called Vernier and they suggested that
we cover
the floor with a piece of carpet. This cured the situation. How can
this
strange effect be explained? The f of the ultrasonic waves is 40
KHz.

Ludwik Kowalski and Richard Hodson
P.S.
Previously posted air resistance data should be ignored; they were

collected without using the carpet.