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FDC1004: Fringing capacitance for electrodes pasted inside container

Riya Gupta
Prodigy 110 points
Part Number: FDC1004

When electrodes are kept inside the beaker the capacitance value at liquid level is completely different from the capacitance value when electrodes are kept outside the beaker.Why is this happening?

Electrodes Outside beaker 100ml =7pf

Electrodes inside beaker 100ml = 30pf

  • 0
    TI__Genius 17440 points

    Hello Riya,

    Thanks for your patience while we were out for the Thanksgiving holiday.

    We call the two setups you've described "direct sensing" and "remote sensing." You can read more about those in this application note. I'm not sure how you've constructed your sensors, but if you've used electrodes like the ones in this TI Design, then the capacitance between them is primarily fringe capacitance. In direct sensing (where the electrodes are directly touching the measured liquid), more of the dielectric between the sensors is liquid, which has a higher dielectric constant than the beaker material. This increases the capacitance between the two electrodes. In remote sensing, more of the dielectric is the beaker material, which decreases the capacitance.

    Best Regards,