How to build in watertight ultrasonic transducer in a watertight box..

Hi fellow engineers

We have designed a range sensor by using this ultrasonics transducer

MCUSD18A40B12RS - MULTICOMP - TRANSCEIVER, 40KHZ, 18MM, METAL | Farnell element14 Danmark

as both a receiver and transmitter

It works fine on the PCB alone. But when we put the PCb into a plastic box, with a hole matching the tip of the sensor, it no longer works

We can make it work by cutting the hole bigger, so that the entire sensor is exposed. But then the box is no longer water tight..

The idea was that it should all be molded into the box, but this will also not be possible since this will require that the hole is tight

So my question is does anybody know how such a transducer is supposed to be installed in a box and still work?

br.

Allan

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michaelkellett over 9 years ago +1

The problem with this kind of sensor is that the entire metal body is part of the resonant structure. They are widely used in car reversing systems so you can look at plenty of examples of how they are…

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michaelkellett over 9 years ago

The problem with this kind of sensor is that the entire metal body is part of the resonant structure. They are widely used in car reversing systems so you can look at plenty of examples of how they are mounted. The basic scheme is to use a soft rubber or silicone gasket or washer between the hard case and the sensor. The performance of the sensor is always affected so you need to make careful measurements and be sure that your production process is well controlled.
The entire conical part of the sensor needs to protrude beyond the soft mounting.

O rings are often too stiff and can give rise to a lot of short time-constant echoes which limit the shortest range you can measure.

MK
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alkrojen over 9 years ago in reply to michaelkellett

Hi Michael

Thanks for your quick reply. Do you know where I can find such a gasket for the sensor?
Have looked at Farnell but so far without success..

br.
Allan
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michaelkellett over 9 years ago in reply to alkrojen

I've never found ready made ones - the easiest way for small numbers is to cast them from silcone rubber. Make sure you get a nice soft kind.
For large numbers you will need to get them moulded specially.

MK
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alkrojen over 9 years ago in reply to michaelkellett

I found this: new design 20khz ultrasonic transducer with red rubber case,China ultrasonic transducer Supplier & Manufacturer - Donggu…
Is it such a rubber case you mean?
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michaelkellett over 9 years ago in reply to alkrojen

That's the sort of thing but a poor example since you would not be able to make it seal up to the main case very well.

Better ones are more like grommets to deal onto the box but for full waterproofness you will need glue as well.

MK
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michaelkellett over 9 years ago in reply to alkrojen

That's the sort of thing but a poor example since you would not be able to make it seal up to the main case very well.

Better ones are more like grommets to deal onto the box but for full waterproofness you will need glue as well.

MK
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