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Original question:

FDC1004EVM: FDC1004: fdc1004qevm

FDC1004EVM: Inquiry Regarding FDC1004QEVM – Detection Sensitivity for Water Droplets

Takashi Matsumura
Intellectual 880 points
Part Number: FDC1004EVM
Other Parts Discussed in Thread: FDC1004QEVM, FDC1004

Tool/software:

Dear TI Team,

The one of our customers is considering an application that involves non-contact detection of water droplets as small as 1 mm in size. For this purpose, he is evaluating the use of the FDC1004QEVM .

In this application, the sensor would be positioned above the target surface. When water droplets appear on that surface, the goal is to accurately detect changes in capacitance caused by their presence.

The customer has asked the following technical questions:

  1. Is sufficient detection sensitivity achievable with the FDC1004 series for this kind of application?
  2. Can it detect capacitance changes caused by water droplets as small as 1 mm in size (in the picofarad range)?
  3. What is the typical detection sensitivity or resolution of the FDC1004?

We would greatly appreciate any insights, reference data, or application notes you could share to help assess the feasibility of this application.

Best regards,

Takashi

T4827447　

  • 0
    TI__Mastermind 40295 points

    Takashi-san,

    We can estimate some potential behaviors of a system based on the FDC1004 if we make some assumptions.
    If they are willing to use the fastest sampling speed (400S/sec) they will get about 17bits of effective resolution.
    With a ±15pF of measurement range, this will give a noise floor of about 30pF/(217) = 0.229fF.
    If we further assume they will need to have a signal +6dB above the noise floor, they they looking for a capacitance change (no droplets → droplets) of about 0.5fF.

    Some very approximate calculations say they could detect the formation of a single droplet 1mm in diameter if the sensor and target are separated by 1.5mm, just a little larger than the dimensions of the droplet itself. This may or may not be a practical requirement, based on their mechanical requirements.

    If they want to detect 10 or more droplets, the distance between the sensor and target can expand to about 5.5mm.
    Thirty or more droplets would allow the sensor/target separation to go to 10mm or less, and 100 droplets would support 18mm separation.

    We might be able to provide additional feedback if they are willing to share additional details of the requirements.

    Regards,
    John