Ultrasonic sensor working underwater?

[arduino__]

I want to use an Arduino and a waterproof ultrasonic sensor to measure distances up to 20cm. Have used ultrasonic sensors in air before but want to know if it will work underwater and if so where could I buy an ultrasonic sensor from? needs to be cheap!!

 

[hevans1944]

I want to use an Arduino and a waterproof ultrasonic sensor to measure distances up to 20cm. Have used ultrasonic sensors in air before but want to know if it will work underwater and if so where could I buy an ultrasonic sensor from? needs to be cheap!!

Well, the United States Navy seems to have good luck with them working underwater. And commercial fish finders seem to work okay too. That is where I would look for an inexpensive waterproof sensor. Maybe try to find a small ultrasonic jewelry cleaner with an intact crystal too. Or wind your own magnetostrictive sensor on a nickel rod with a few (or a lot of) turns of insulated magnet wire. Might want to read up on acoustical coupling though, to get a good mechanical impedance match between the solid rod and liquid water.

Project sounds doable. Not necessarily cheap though if you purchase ready-made. Let us know what you find for ultrasonic transducers.

 

[(*steve*)]

well, it likely won't be cheap, and since sound travels faster in water than air, the time delays will be correspondingly shorter.

 

[Alec_t]

What sort of water depth do you want to work at? If very shallow, you may be able to adapt the usual air-type transducers.

 

[(*steve*)]

The problem with adapting a transducer designed for air is that there is a large mismatch at the air/water interface resulting in a poor transfer of energy.

 

[Alec_t]

Granted; but depending on the transducer spec there may still be enough transferred energy for the 20cm range the TS requires.

 

[arduino__]

Thank you for your replies would this work?
http://www.ebay.com/itm/Ultrasonic-...ducer-Sensor-Perfect-Waterproof-/321714364470

 

[Alec_t]

The link doesn't give enough info to judge. Looks like it's intended to operate just in air but be weather-resistant.

 

[mgrass]

I have used that waterproof transducer and it works ok, but it's blind from 0-25cm(check the specs on ebay). The one I used actually worked to about 20cm. Once your less than 20cm, the reading were erratic and in the range of about 90cm (if I remember correctly). Because sound travels faster in water, the blind range may be 0-30cm. SO, I don't think it will work for you. I have also used some of the HY-SRF05 (SRF05) and the SRF04. Some of the SRF04 were giving me some very erratic readings. My guess was that the mechanical part inside the transducer was loose. I removed the screen from the transducer and then spayed clear enamel on the inside of it till it was well soaked. Sprayed the outside of the board as well. I then let the sensor drain upside down at a 45 degree angle so the excess could run off and not leave a drop hanging from the center piece. Let it dry /baked in an oven at 230F for a couple hours, then cool. It fixed the erratic readings. Why am I telling you this? Well those transducer modules are cheap $2.00usd or less. Make you connections to the board...solder them. Then coat your module with epoxy or polyester resin (2 part). Don't use the quick set type. With the face of the sensor pointing down at a 45 degree angle, heat it with a heat gun/(hair blow dryer). When the resin heats up, it will become thin before it sets up. The excess resin will run off. Let it cure. You can bake it in the oven for an hour or so at about 200F. You now have a sensor module that should work for the range that you want. I'm just guessing it will work. It certainly SOUNDS (pun intended) like a cool experiment. Let us know what happens if you try it.

 

[arduino__]

What would my code look like with the adjust of water?

 

[Alec_t]

What code? If it's something relating to measuring distance in air then you would need to reduce timing values to acount for the higher speed of sound in water. Of course, you might also need to adjust those values as a function of temperature, salinity etc.

 

[Fish4Fun]

I ordered one of those linked ebay "waterproof" transducers.....hoping to use it underwater....but when it arrived it is as stated above....more "weather resistant" than "waterproof" and certainly not instilling a lot of confidence it will work "underwater"....that being said, I want to use mine to measure the water level in a cistern, and I think it might actually work for that if I simply epoxy it to a piece of FR-4 (obviously no copper on it) and then "float" the FR-4 so the sensor moves up and down with the water level (it would always be sensing the "bottom of the cistern", but the distance would decrease as the water level dropped...) I haven't had a chance to play with it yet, but will report back if I have success....

Fish

 

[hevans1944]

I want to use mine to measure the water level in a cistern

So why not just mount it above the water and measure the distance to the water surface? That distance will increase as the cistern is emptied.

 

[Fish4Fun]

Hey heavans1944!

That is on my list of things to "try", but I am worried that w/o being epoxy encapsulated that humidity might cause problems....I am also uncertain how the "echo" effect will play out....I actually have two cisterns that need such a device...one is ~10ft in diameter but only ~36in tall, the other is ~30in in diameter but nearly 7ft tall....both have a lot of "echo" when near empty....I have NO idea how that will affect these devices, but my thought was the effect would be dampened by being underwater....but that could prove 100% wrong, LoL....I am currently using float-switches on one....but the failure rate is higher than I would like....for the other I built a float with a guided rod and a "flag" that trips an upper and lower limit switch....it has been in service ~ 3 years and has been reliable to date....

Fish