Electronics > Metrology

Millimeter range water level sensor

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Hello Guys, I wonder if I should post this in the "Projects" or here.

I'm brainstorming ideas for a millimetre range water level sensor. The water is in a plastic tube of 3mm ID (I can re-engineer it to a different shape, but the water column cross-section area needs to stay fixed). The level fluctuations are within 5mm. My target resolution is 0.2mm and the target data rate is 50Hz.

Any clues on the technology I could focus on? Resistance of two submerged electrodes? Parasitic capacitance difference of a submerged inductor?

I want to obtain the data using a microcontroller later on.

Thanks a lot in advance.

I'm going to imagine that surface tension, capillary action and wetting of surfaces could be complicating factors here. Maybe an ultrasonic depth gauge, or resonant frequency of the tube (either the air cavity or tube as a whole)?

Is the tube permanently fixed, infrequently swapped or (for example) a disposable sample tube?

What came to my mind is capacitive sensing with sense electrodes on the outside of the tube. What’s the material and wall thickness expected to be?

Oh yes… if sample tube is transparent then maybe an optical method is possible…

Using the conductivity with an electrode only works if the conductivity of the water is well defined - this is tricky with pure water as tiny changes in the PH can have a large effect.
Not so clean water may lead to a biofilm, that could effect electric and also capacitive measurements.

The surface tension can be a real issue. Because of the extra surface I would avoid an extra electrode.

Ultrasonic looks promissing. Simple optic from the outside should also work, but could be effected even more by the surface tension / surface shape.

Have a look at these.


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