MaxSonar EZ1 Sensor......Outdoors?

Hi all,
I've been using the MaxSonar EZ1 ultrasonic sensor for the past month or so and am very pleased with its performance. Up until this time,
I've been using it indoors. I now have a need to get similar results with it outdoors. I didn't think this would be a problem, but the datasheet says "designed for indoors" and this has made me a little worried. I'm guessing it's because surfaces indoors tend to be nice and flat as opposed to outdoor surfaces? Has anyone used this sensor outside before?
Thanks in advance, -weg
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On Feb 16, 9:41 am, snipped-for-privacy@drexel.edu wrote:

I would guess that means, don't get it wet. It is not conformally coated or in anyways hardened against the weather. I don't think the physics of anything changes outdoors. Of course temperature effects the time of flight, so your readings will be off if the temperature is different from room temp, but it's a minor correction. But I doubt you'll be flying your helicopter anywhere or anytime that isn't as bad for your brushless DC motor (assuming that's your power) as the sonar.
-- Randy M. Dumse www.newmicros.com Caution: Objects in mirror are more confused than they appear
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RMDumse wrote:

Wind does. The Polaroid sensors are pretty good outdoors, and in fact that's what they were designed for. But also they were designed for use when the subject was typically 6+ feet away. If you're trying to detect an object a couple inches or a couple feet away, the wind shouldn't affect the readings all that much.
-- Gordon
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wrote:

Hi Gordon, any comment or idea on why? I thought about mentioning wind, because I've heard it before, but decided I couldn't support an objection. Speed of sound in air is roughly 1100 ft per second. A 30 mph wind would be 44 ft per second. Error should be minor in the hundredths place. Humidity also bears on speed, as would altitude, but I don't know if any of these would be very noticable. Ideas?
-- Randy M. Dumse www.newmicros.com Caution: Objects in mirror are more confused than they appear
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RMDumse wrote:

Average air velocity is not a principal factor; turbulence (i.e. spatial heterogenity) is the main factor. Light speed is much more than sound speed, but turbulence is a main obstacle for optical observation/measurement too.
Nick
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RMDumse wrote:

I don't know precisely why, but there are ultrasonic sensors for measuring wind direction and velocity (quite accurate, too), so I assume the change in transit times across the T/R pairs is appreciable enough to make a difference, though whether it's enough to impact the measurement beyond the natural error of the device I don't know. However I do recall reading a white paper from Polaroid on how the frequency sweep system employed in their large transducer design mitigated the effects of wind. They were quite proud of it in fact.
I have also seen a couple of people note spikes in the output when using the Ping outdoors in windy and/or wet weather. Caught some of it on discussion boards related to measuring snow depth. Can't seem to find them now...
-- Gordon
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Gordon McComb wrote:

These work by measuring the transit time from A to B, and orthogonally from C to D, and adjusting for temperature. The sonar distance sensors OTOH measure a reflection A-B-A, where the effect of wind in the forward path is cancelled by the same wind on the reverse path.
Clifford Heath.
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Clifford Heath wrote:

That doesn't make sense. If you have a wind that is perpendicular to the direction of the sound wave, the return beam will not somehow find its way back along the same path. Its return will be sheared the same amount and in the same direction *away* from the original signal source.
-- Gordon
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Gordon McComb wrote:

Yes, but if you do the sums, comparing with the speed of sound at 342m/s, you have to get a *very* strong wind to get much inaccuracy. I guess if a few percent matters you might care, but for navigation, it's negligible.
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Clifford Heath wrote:

Just to put numbers to this, a 60 knot wind is about 30m/s. arctan(30/342) is a 5 degree slip angle, and 1-cos(5 degrees) is 0.0038 - less than half a percent of error. In that much wind you'd have trouble hearing your ping anyhow.
Clifford.
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Clifford Heath wrote:

I see your point now, but I don't think it's just time-of-flight that matters here. I brought up the ultrasonic wind sensors because clearly these devices are accurate enough to detect changes in wind direction/speed just by comparing differences across a pair of tranmitters/receivers. Beyond that though it's somethiong of comparing apples to oranges. I think one thing to concentrate on is the "mirage" effect and how air turbulence can distort the reading.
But probably more critical is that an ultrasonic receiver is effectively a microphone (though admittedly with somewhat different characteristics than a 20Hz-20kHz mic). Anyone who has used a microphone outdoors in the wind knows about the unpleasant "pops" of sound that occur when the air hits against the element. If a reading takes place right at the time of a pop it'll be an invalid measurement for sure.
-- Gordon
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Clifford Heath wrote:

and from B to A. after which these 2 measurements are subtracted ;-)
Stef
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The low cost 40khz piece-o-electric
have very high Q and ring forever
if you take them outside where those
frequencies are much higher .
Thats why Poloroid created
a higher voltage "electrostatic"
method ( opposed to Piezo) ,
which has not the Q
or "storage" of energy , thus they
can quickly stop , after sending
out a pulse . They stop so quick ,
one can measure very short distances .
The best use for P' is to chase away
mosquitos .
Im doin mcu's , just got lots of Ninetendo
DS lites and ARM7 mcus . Ill be cutting
down the size of s/w , handing out a free
Op System soon .
Ill test the Op Codes and other stuff ,
like USB , on the ARM7 mcus and
then write a new Op Sys for the NDS lites.
I will tunnel RS232 and even USB and
EtherNet and the ARM loader and CAPS
and Angel and IDE's and .....
A new Op Sys , without text input !
On Feb 16, 8:41 am, snipped-for-privacy@drexel.edu wrote:

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I have heard reports of the MaxSonar-EZ1 sensor working very well for use in flight both (blimp and helicopter) use. At least one small model helicopter company compared the outputs from the MaxSonar-EZ1 to other sensors, and then selected the MaxSonar-EZ1.
The MaxSonar-EZ1 Calibration Cycle is very useful here! One thing the helicopter folks did was wait to take the first reading until in flight, so the calibration cycle would adjust for conditions (even ambient wind noise). They reported that the readings were useable and stable, even during flight.
(PS. Unless you build a special housing, don't fly in the rain.)
Bob Gross CEO MaxBotix Inc. www.maxbotix.com
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