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Electrich • Dec 14, 2016

[Safeguard] Best way for product to only work when in water?

Hi guys,

I'm developing a product that will be submerged only 1-2 feet under water while 1/3 feet of the upper body will be above the surface. The tech is not intended to be used when not in water as it generates some heat and may gradually destroy it's main components if used dry over time.

What I'm looking for is a good and cheap method to safeguard this for our customers. Considering the product is waterproofed, how to correctly sensor water location by a few inches? The product can only be started by app through BT or WiFi. So the goal is to not be able to turn it on in the app if the product's sensors detects no water around or on its body. Also it's preferred, but not necessary, that it auto stops the process if pulled out of the water.

Will those cheap ultrasonic sensors work if connected to the programmable chip? Or are there any better, more safe methods that you would recommend me looking into?

Thanks in advance for any help!
- Ed
[Prototype] • Dec 14, 2016
I am not sure how you'll use ultrasonic sensor for detecting presence of water.
If you don't have a strict requirement for a solid state sensor then I think you can do something with a simple float. You can implement it in multiple ways. You can use it to directly cut the power or get some digital output and invoke a software routine.
We use low pressure mem sensors in medical instrumentation for detecting pressures up to 30 inches water. These consume very little power. The sensor can be mounted on any electronics being used. A silicone or other tube can lead from the sensor to the lowest point (Bottom of the submerged enclosure?). The out put from the sensor is linear with the depth of immersion and can be used to control, generate alarm and such.
There are many brands. Here is one:
Electrich • Dec 14, 2016
By ultrasonic sensors/receiver in a waterbed of steel (similar to that of those industrial cleaners, varying in size) I thought about, if possible, to compare the difference between the waves that goes through water and those that go through air. The waves will travel slower and diminish faster in water compared to air, thus giving poorer results on the way back, as a trigger that it's ok to keep the product turned on. If the receiver picks up too strong signals (=air), it will stand by. Not sure if it's something that would work or if it's any good at all compared to other appliances and alternatives.

The challenge is that the product is enclosed and will need to have a high standard, ip67 or above. So it needs to be something that can measure what's outside the box without being attached to the outside.

Ramani, thanks, those seemed very interesting! And maybe even for more purposes than just this one. Will read up and see if there's something we can use, but it definitely looks promising!
Many IP 67 compliant diaphragm swiches and sensors are available. This one is a factry settable switch:
Pressure Switches | baccara
There is a much simpler option, if the water is plain water and not distilled water.
If the minimum level required is known and fixed, all that is needed is to stick two foils of copper (Copper is not susceptible to algal growth) about 2 square centimeters area at that level out side the tank. If the container is metallic these have to be insulated from the metal. When the electrodes are immersed in water the resistance between them is much less than when they are in air. This can be used to control other actions like switching off power if these are exposed.
Incidentally, I have personally used this concept in a medical device, where it has been performing consistently to the stringent requirement of applicable standards.

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