Environmental susceptibility of ping sensor

Carl Hayes

I'm idly considering the Parallax ping sensor as a means of gauging the fresh-water tank in my motor home.· I'd cut a couple holes in the top of the tank, install the sensor, and use a Stamp to gauge how much water is in the tank.

I have no experience with that sensor, and have never seen one.· How robust would it be at the top of a polyethylene water tank?· Is it waterproof?· If not, can it work through, say, a thin membrane such as Glad Wrap?· I'd welcome anyone's experience.

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· -- Carl, nn5i@arrl.net

Post Edited (Carl Hayes) : 12/11/2008 6:30:43 PM GMT

Franklin

This has been discussed here before. There should be hits if you use the google search on the parallax home page. The answer to both your questions is not likely.

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- Stephen

Carl Hayes

Thanks, I think. I can keep it dry, and I wonder if anyone -- who actually knows -- can answer whether it will work through a membrane such as Glad Wrap, stretched taut. Would anyone who has a Ping be willing to stretch a piece of Glad Wrap across the front of the thing, and run an experiment to find out?· I need only about two feet of range.

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· -- Carl, nn5i@arrl.net

Franklin

www.google.com/search?hl=en&rls=com.microsoft%3A*&q=site%3Aparallax.com+waterproof+ping

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- Stephen

Carl Hayes

Thank you, Franklin, or Stephen -- not sure which name to use.· I read all those, but none address the question of whether a PING can work through a thin, taut membrane.· Instead they all contemplate placing the whole thing, or whole PING, underwater.· Of course I never contemplated doing that.

Also, of course, all the answers you point to·are guesses by folks who don't really know and haven't run any tests to find out.· If guesses are all I can get, I'll test my own guesses before cutting any holes in my fresh-water tank.

In consequence of your earlier suggestion I had definitely learned that the transducers are not protected from environmental hazards; and I concluded that a membrane would be necessary.· But the tank is inside the coach, and with a membrane between the sensor and the opening in the top of the fresh-water tank the sensor would stay perfectly dry.· So now (as I said before) I need to know whether the PING will work through a thin, taut membrane in air.

My best guess is that the device will work through a membrane.· Thin membranes of low stiffness and low mass tend generally to be reasonably transparent to pressure waves, though not to shear waves·(in fluids like air, sound waves are always·pressure waves).· That's why I hate it when·my neighbors·drive around the neighborhood with boom boxes playing unmusic; my windowpanes, considered as glass membranes,·are thin enough and flexible enough·and of low enough mass to pass the low-frequency noise.

Still, I had hoped someone might take a few seconds actually to try it on my behalf, before I spend money on something that I think, but do not know, will work.

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· -- Carl, nn5i@arrl.net

$WMc%

Mr.Hayes

I have done a few projects with the PING. The one that comes mind is the vehicle/cow detector on My gate opener.
I made an enclosure where only the transducer stuck out. I then covered them with clear shrink wrap and a large pvc hood to keep the sun light off the shrink wrap.This has been in service for 2 years now.

The shrink wrap is the food grade type."Like what You would use to wrap leftovers with"

I did lose a little long range detection, But it would still read to ~ 24"s



_____Hope this is of help_________________$WMc%___________Merry Xmas

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The Truth is out there

Carl Hayes

Cool, $WMc% -- I still wish I knew how to pronounce your name -- that's exactly the sort of response I was hoping for.· Very helpful!· Thanks -- and Merry Christmas to you, too.

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· -- Carl, nn5i@arrl.net

SRLM

I tried it to see what happens. I used a thicker plastic than saran wrap, it's about the thickness of a cheap sandwich bag (slightly thicker than a regular grocery bag) I stretched it tight, and nothing happened. No signals made it through, so it maxed out on the range. Moral of the story is that the plastic has to be really thin.

Tracy Allen

Hi Carl,

I was involved with development of an ultrasonic "locator", link here, for which we had to test the transmission of 40khz sound through materials and within the confines of rooms. The loss through single layers of 0.6 mil polyethylene (garbage bag) was about 6dB (1/2 the voltage). If there were to be a membrane on both the transmitter and receiver, as in the Ping, I'd guess there would be twice the attenuation. I'd think on that basis the PING has enough punch to work with a little less range, as $WMc% has shown with the gate opener. In doing tests on these materials, we quickly realized how sensitive the results are to wind currents and to other sources of experimental error.

Out of curiousity and for protection of the transducer, I also tested Gortex microphone membranes.. They are not speced up to 40khz, but they do in fact work very well there. The attenuation is less than 3dB.

There are special ultrasonic transducers that are environmentally sealed. Instead of an open screen on the top, through which you can view the cone, they have a solid metal membrane on the top. The ceramic resonator is attached directly to that membrane. They are a bit less powerful/sensitive. But if you are looking for something to sit on top of a water tank, I imagine you could find a suitable one to swap for the open ones on the PING. One manufacterer of these things is Prowave (Newark, Farnell)

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Tracy Allen
www.emesystems.com

$WMc%

Mr.Hayes

One thing I didn't mention was water droplets on the membranes.This will cause big errors with the ping,as My gate doesn't like to open or close in a hard rain. At first I taught the ping was picking up the rain but later I found the membranes were wet,I dried them off with a soft tissue and viola. I modified the hood I made and it helped a lot, But every now a then they'll get wet.

A stand pipe might work for Your app. to keep water from splashing on the transducers,if You have the room!


______________________$WMc%_________________Merry Xmas

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The Truth is out there

kelvin james

Here is another approach which lets you use the ping to its full potential.


I figure since you only need to do periodic checks on the tank, how about a actuated flap cover for the ping mounted in a tube. You could use a cheap solenoid to open and close it for readings, and would be basically water-tight using a rubber face on the flap. With the proper lever mechanism, all electrics would be outside the tank.

Maxbotics makes a so-called waterproof sonic ranger, but it costs $100.

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Oops. It should be Maxbotix, Sparkfun sells all their sensors.


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Post Edited (kelvin james) : 12/14/2008 4:53:22 PM GMT

P!-Ro

Try IR. I know the water is clear, but you could probably pick up the glare off of it.

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PG

Carl Hayes

Thanks much to all. I'm going to look into the Maxbotics device if it's $100, because after I have custom PC boards made, buy the Ping, and so forth I'll likely spend that much anyway. But the information y'all have provided is a great boon. Again, thanks!

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· -- Carl, nn5i@arrl.net