Hi folks,
I have bought a few ultrasonic sensor modules HC-SR04's

Now I know that they are not high quality devices and my expectations are suitably tempered, essentially I am just playing and may look at better units or modifications to these if my experiments look promising.

I want to try measuring the distance to the surface of water, only a meter or so, if it doesn't work then I will need to look at options, a float perhaps.

Two questions...
Am I likely to have problems if the sensor is inside a tube, 100mm or so, along with the surface I am trying to sense?

I will want to pot the board which should be fine, but I would also like to damp proof the transducers, can I cover them with a membrane of any sort without attenuating the signal too much?

Any and all comments welcome, thanks
Al

 

Some problems encountered in using Ultrasonics were restrictions of tube ID and material vs. sensing distance. You don't want to attenuate the signal with metal (take metal away). You should be able to read right thru an epoxy coating.

Cheers, DPW [Everything has limitations...and I hate limitations].

 

Have you thought about using an ultrasonic transducer as used as a part of a small boat's fishfinder?

 

I used to work for an ultrasonic company, but much of what we knew was not firmly based in theory as the guy who developed the basic transducers had long left the company. But what is true is the signals are waves, analyze just like any other wave phenomena (ie, Snell's Law applies for reflections).

When hitting a boundary (such as air to water) there is some reflection and transmission, the fractions depend in the acoustic impedances of the materials on each side of the boundary. While your sensor works in air our sensors worked thru the medium as we shot them up thru the walls of the chamber and then thru the water, and back.

I've never really worked much with these "air" sensors though I have some in my parts box. We made our sensors from sheets of crystal material scribed and snapped to size, then epoxied to the sensor face, which was applied to the chamber. We'd use hard plastic for soft materials, and soft plastic for hard materials. So it may work if you fill the sensors with epoxy (no air bubbles!) and make then solid, so you can measure "bottom-up" thru the tank you have.

It would make an interesting experiment I don't have the time to try. <grin>

You can find some good reading here: http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/cc_ut_index.htm

 

Thanks folks ... That link has some deep stuff, much reading later I think.

I had thought of different sensors, ones designed for car reversing sprang to mind as being available weather proof and comparatively cheep.

I bought the little board, only a couple of quid, to play with, essentially just to prove, or debunk, the concept, ultrasonics in a tube I mean.

 

An ultrasonic fogger has a piezo transducer that is designed to work when immersed in water. Get one.