Hi,
I am trying to determine if the FDC1004 is suitable for a product we are designing (liquid level detection for plain tap water).
We are measuring the height of water in a reservoir, but when the reservoir is emptied quickly the measurement falls behind and takes a lot of time to get to the right level. Something like the topic starter in: e2e.ti.com/support/sensor/capacitive-sensing/f/987/t/477949 (adding https:// makes the form act weird).
When investigating this problem we found that a very thin water film forms on the surface of the reservoir which takes more time to "fall down" the side of the container. This effect gets worse after a few days of water going in and out of the reservoir. Applying a greasy substance to the surface solves the problem, but this is not a solution in our case unfortunately. We have tried a ton of different materials (mainly plastics) for the reservoir but all of them fail after a few days. We also tried coatings but they have to be food-safe and very durable, which is a tough combination.
Another solution would perhaps be to not measure using the fringe field principle, but with two plates opposite each other (like a "normal" capacitor). This way the thin film will not affect the measurement as much as it does now. The volume/parasitic capacitance of the film will be tiny compared to the total capacitance of the capacitor formed in this setup.
This is the topology I would like to use for the main electrode (not to scale ;) ) :
Shld2 Shld2 wall water(10mm) wall CIN1 Shld1
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And for the reference:
Shld2 Shld2 wall water(10mm) wall CIN2 Shld1
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Set CIN1 to differential with CIN4 (floating)
Set CIN2 to differential with CIN4 (floating)
Symmetry and placement of electrode will be very precise.
So the question is: "Can I use the OoP technique like this?"
Regards,
Tom
