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Ultrasonic Sensor Project - Water!
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Please be positive and constructive with your questions and comments.

Ultrasonic Sensor Project - Water!

by DirtyWilly on Thu Oct 06, 2011 4:01 am

Hello, I have a simple yet challenging question about ultrasonic sensors and how well they perform when wet.

How well would a sealed ultrasonic sensor perform if there was a single droplet of water on it?

The standard mesh ultrasonic transducers and receivers pretty much don't work at all when wet, but this is due to the water droplet forming a barrier in the mesh preventing the speaker from transmitting or receiving a pulse. A "canned' or sealed waterproof ultrasonic sensor is resistant to water and has no mesh, but can it still accurately transmit and detect pulses if so much as a drop of water is on it? Since the majority of them are advertised as waterproof, I would like to think that minimal water wouldn't significantly affect the sealed sensor, but the questions remains, will it still take an accurate measurement?

Here is an example of a sealed ultrasonic sensor.
http://www.dfrobot.com/wiki/images/5/52 ... _proof.jpg

Could use help on this!
DirtyWilly
 
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Re: Ultrasonic Sensor Project - Water!

by adafruit_support_bill on Thu Oct 06, 2011 6:13 am

but this is due to the water droplet forming a barrier in the mesh preventing the speaker from transmitting or receiving a pulse.

Even units without a covering mesh will fail. Any water that reaches the transducer diaphragm will change its resonant frequency. From experience, even a single drop of liquid on the diaphragm will result in wildly inaccurate reading, if not complete failure.

I would like to think that minimal water wouldn't significantly affect the sealed sensor, but the questions remains, will it still take an accurate measurement?

Water on the shroud might decrease the range a bit, but should not change the accuracy appreciably. What does the manufacturer have to say? I've had good luck with the weather-resistant Maxbotics units.

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Re: Ultrasonic Sensor Project - Water!

by DirtyWilly on Thu Oct 06, 2011 11:02 am

@adafruit support, first thank you so much for getting back to my posts so quickly.

I did contact the manufacturer and he said that the accuracy would not be effected, however the sensitivity would. He also mentioned that for distance measurement a droplet wouldn't effect the travel time of the sound pulse so as long as my application wasn't sensitive, distance measurement should be unaffected. I can't seem to wrap my head around the difference between the accuracy and sensitivity in this case for a reliable distance measurement, but like you have both hinted, I should have good luck with a sealed sensor.
DirtyWilly
 
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Re: Ultrasonic Sensor Project - Water!

by brucef on Thu Oct 06, 2011 3:11 pm

DirtyWilly wrote:I can't seem to wrap my head around the difference between the accuracy and sensitivity in this case for a reliable distance measurement, but like you have both hinted, I should have good luck with a sealed sensor.

Accuracy: The ultrasonic signal will take the same amount of time to bounce off the target and return, so the distance measured won't be affected.

Sensitivity: The signal may be reduced in strength due to the presence of water. Therefore if the signal is weak in dry conditions, the sensor may have trouble picking it up at all when wet.

That's my interpretation, although I haven't worked with these sensors myself.
- Bruce

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Re: Ultrasonic Sensor Project - Water!

by DirtyWilly on Thu Oct 06, 2011 4:45 pm

Hey BruceF! That was my assessment as well. It was one of those I was sitting at work dull tasks moments when it just popped in there that maybe sensitivity was in reference to something like distance or shape of the wave.

Hope were right! :P
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Re: Ultrasonic Sensor Project - Water!

by 123Splat on Wed Oct 12, 2011 1:35 pm

Willy,
Have you thought about trying something using Crystal Earphones, like you used to get with transistor radios. The work in fresh water environs between, about, 20 - 40 kHz. Use phase shift to detect returns and calc distance emperically. Curde, but gives results.
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Please be positive and constructive with your questions and comments.