Date: Thu, 14 Oct 1999 06:27:37 -0500

Author: (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: " Forum for Physics Educators"
>Reply-to: " 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 back before the next pulse is 1.4 m.
>Of course, the pulse may arrive during the second listen time and that
>throws the whole thing off. How is it determined that the detected echo
>is from the most recent ping and not some past pulse? Sounds like
>another lab day to me.....
>Pete Lohstreter "Reality is merely an
>The Hockaday School albeit a very persistent
>Dallas, TX 75229 A.

Dr. Karl I. Trappe Desk Phone: (512) 471-4152
Physics Dept, Mail Stop C-1600 Demo Office: (512) 471-5411
The University of Texas at Austin Home Phone: (512) 264-1616
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