• Resolved

FDC1004: FDC1004 FDC2214

Part Number: FDC1004

Hi.

I followed datasheets and guides for liquid level sensing applications using FDC1004, and have several questions about it.

1) There is note in SNOA925 which says the following: "Liquids that cannot be used for liquid-level sensing include oil-based liquids, soap, or a liquid with a sticky or slick residue." Oil-based liquids cannot be used becuse they are sticky, or is there any other reason? I understand that slick residue must reduce precision. But what if I use 3-channels setup and measure empty-space (environment) capacity, and environment sensor is covered with slick residue, too?

2) If I cant exclude liquid sticky or slick residue factor, is it possible to use capacitive approach to measure relative changes in liquid level with precision of at least 1 cm for 3m tank height?

3) If condensate may appear on tank walls (and sensor, too), then capacitive approach won't work at all, I guess?

4) My client needs to measure liquid level in a plastic tank with height from 1 to 3 meters with worst-case precision of 1 cm (goal is 1-2mm). I read another discussion ("Longer sensor length"), and expert said that FDC1004 will most likely saturate and recommended FDC2214. Can you give a recommendation what would be better - reducing track width (that would be around 1-2mm, depending on liquid dielectric constant and actual tank height) and using FDC1004, or using FDC2214 with wider tracks?

5) There is approach called immersive straw in SNOA934. Will it provide performance improvement, compared to single flat PCB covered with thin layer of plastic and placed in the center of tank directly into the liquid? In this case there won't be air gap between rear part of sensor and liquid.

6) Distance from the center to the edge of plastic tank is 30cm or more. According to SNOA934, level error for hand placed at 5 cm from sensor is 1.83%. Which means in my case FDC2214 would be better despite of OoP functionality of FDC1004 if placed in the center of tank. Please correct me if I'm wrong.

Thank you.

  • Hi Artyom,

    For oil-based liquid, the dielectric constant can be much lower than water, so the sensitivity will be reduced.

    3m height is very tall. We have not tested any sensor of this scale. FDC2214 should be the better option.

    You can do a quick test by connecting some copper foil to the EVM, then check the noise floor and dynamic range of the signal. This way you can tell if the setup is feasible.

    Regards,

    Yibo