Date: Thu, 14 Oct 1999 06:27:37 -0500  Author:
trappe@physics.utexas.edu (Karl Trappe)  Subject: ultrasonic
update   This info from Norman Lohstreter should explain some of
the curious effects we have observed in using the ultrasonic
rangers. I had wondered what was causing the distance limit to
vary. Karl  >Date: Wed, 13 Oct 1999 22:08:12 -0500 >From: Norman
Lohstreter >Subject: ultrasonic update >Sender:
"phys-l@lists.nau.edu: Forum for Physics Educators" >To:
PHYS-L@lists.nau.edu >Reply-to: "phys-l@lists.nau.edu: Forum for
Physics Educators" >I just finished the O'scope analysis of the
Ultra sonic motion detector >this afternoon. >Here's what I
discovered; >The Ultrasonic frequency is 50kHz with a 50% duty
cycle. >Each query consists of 17 of these pulses (350 uSec)
followed by a >Depending on the number of queries demanded, 10
per sec, 25/sec, or >120/sec, the pulse will have from 100 mSec
(10 Hz) to 8.33 mSec to >receive the echo. >This means at 120
Hz, the maximum distance the pulse can travel and >get