Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ihnp4!inuxc!iuvax!iucs!silver!commgrp
From: commgrp@silver.UUCP
Newsgroups: sci.electronics
Subject: Re: Ultrasonic Distance Measurement
Message-ID: <24300004@silver>
Date: Fri, 13-Mar-87 09:33:00 EST
Article-I.D.: silver.24300004
Posted: Fri Mar 13 09:33:00 1987
Date-Received: Sat, 14-Mar-87 09:40:13 EST
References: <8455@aero.ARPA>
Organization: Indiana University BACS, Bloomington
Lines: 46
Nf-ID: #R:aero.ARPA:-845500:silver:24300004:000:1831
Nf-From: silver.bacs.indiana.edu!commgrp    Mar 13 09:33:00 1987




The Polaroid Ultrasonic Ranging System is a sophisticated device; it
emits a successive burst of multiple ultrasonic frequencies (similar to
the swept-frequency chirps of bats) in order to eliminate flase readings
caused by resonances.  Receiver gain is increased in a series of timed
steps after each pulse is transmitted, to reduce false readings caused
by echoes from nearby objects not in the main beam (surprisingly narrow;
-3 dB width about 8 degrees).  The unit is supplied with excellent
documentation. (I'll Xerox schematic for SASE.)

I bought one several years ago, to use for measuring ceiling heights,
etc., in cave-mapping.  I installed it in an old Civil Defense
geiger counter case.  The shell of a military-type connector, with
screw-on cap, protects the transducer when not in use.  I mounted a
flashlight reflector/bulb assembly in the meter-hole of the case, and
connected it to a pair of D-cells; the light is essential for aiming the
narrow beam.  The rangefinder itself uses a 6-volt flat Polaroid "letter
bomb" battery.

The unit's digital readout indicates feet and tenths of a foot, to a
maximum range of 30.4 feet.  I have not tried to extend the range.

One problem with the rangefinder, probably not significant to most
people, is that it's incompatible with bats!  Its pulses seem to disturb
them severely, and when used in the presence of bats (I don't know the
species), it gives random readings.

There's an ad for the Polaroid ultrasonic rangefinder in SENSORS
magazine, March 1987, p. 27.  

Polaroid Corp
Ultrasonic Components Group
119 Windsor Street
Cambridge, MA 02139
ph:  (617) 577-4681

The Polaroid Ultrasonic Ranging System Designer's Kit cost $165 (too
much in my opinion, but they've got a captive audience).

Frank Reid
PO Box 5283
Bloomington IN 47402

reid@gold.bacs.indiana.edu