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Moisture sensing

Alvin P. Schmitt
Intellectual 940 points
Other Parts Discussed in Thread: FDC1004, FDC2212

I have a patented sensor that uses fringing fields to sense moisture on top of plastic sheet. Two runs interleaved on the top do the sensing at 13.56 MHz. From dry to totally wet involves 1 pf change. Must work from 29 F to 129 F. Would the FDC1004 work in this? I guess one connection (active) goes to one run; ground goes to the other run and shield goes to the bottom with fr4 in between. Fringing field is above flat sensor. I just need one sensor not 4.  Its normal dry capacitance is 62 pf. Please point me in the right direction documentation wise. Thank you

  • 0
    TI__Expert 8050 points
    Hello Alvin,

    Did you mean you already have an active signal driving the interleaved sensor at 13.56 MHz? What's your requirement on sampling rate and resolution?

    Regards,
    Yibo
  • 0 in reply to Yibo Yu
    Intellectual 940 points

    I currently use a phase lock loop. 13.56MHz is so the fcc does not get me if a signal leaked out. I guess the fdc1004 would energize the sensor but I know nothing about it.  The resolution is from 62pf totally dry to 63pf totally wet. will take any resolution down to 256. Sample once a second would be fine as it will evaporate the fastest at 2 minutes full sun. Most of the time 12 to 20 minute evaporation time from wet to dry and needing mist again.

  • 0 in reply to Alvin P. Schmitt
    TI__Expert 8050 points
    Hi Alvin,

    FDC1004 should work but it may be susceptible to noise from the 13.56MHz signal. A better solution is FDC2212, which has better noise immunity and higher resolution. The trade-off is that FDC2212 does not have an active shield driver, so you may only use the ground as the shield.

    Regards,
    Yibo