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From: phd@speech1.cs.cmu.edu.UUCP
Newsgroups: sci.electronics
Subject: Higher accuracy Ultrasonic Rangefinding
Message-ID: <1001@speech1.cs.cmu.edu>
Date: Sun, 15-Mar-87 04:43:00 EST
Article-I.D.: speech1.1001
Posted: Sun Mar 15 04:43:00 1987
Date-Received: Sun, 15-Mar-87 19:36:32 EST
Distribution: na
Organization: Carnegie-Mellon University, CS/RI
Lines: 30
Keywords: Ultrasonic, Rangefinders

Does anybody out there know what the fundamental accuracy limitations
are for Ultrasonic rangefinders? I would guess that air temperature
and pressure changes would severly limit performance.

A previous post mentioned the severe ringing of most ultrasonic
transducers. For single transducer systems, this is especially
troublesome, since one must wait for much of the ringing to die
out before looking for an echo. Does anyone try to actively damp
this ringing?

Most of the detection circuits I've seen (i.e. National's LM1812)
just use some sharp filter to look for the echo. Since the signal is rather
slow, wouldn't it be better to perform some sort of cross-correlation
between the transmit and receive signals. This way, a somewhat more
random looking signal could be used in noisy environments. (Is this
what the Polaroid system does?) Intuitively, I would expect the
cross-correlation to give more accurate results, if one could get
a transducer to do more than just oscillate sinusoidally at its
resonant frequency.

Has anyone tried any of these things?

--- Paul Dietz
Dept. of Electrical and Computer Engineering 
Carnegie-Mellon University
Pittsburgh (America's MOST livable city!), PA

phd@speech1.cs.cmu.edu.ARPA

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