Re: ULTRASONIC MOTION DETECTORS

[brian whatcott <inet@intellisys.net>]

Motion or movement sensors may use either doppler or pulse delay methods.
Position sensors would use pulse delay.
It may be that a particular pulse transducer uses a narrower pulse when the
pulse repetition frequency is increased - and this narrower pulse might be
more susceptible to obtrusive multi reflections or other calibration error...

Brian
 
At 08:46 12/5/97 -0400, you wrote:
> 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.
brian whatcott <inet@intellisys.net>
Altus OK