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FDC1004: problems with unstable measures and identical measures

MAZIERE Herve
Prodigy 40 points
Part Number: FDC1004

Hi everybody,

I'm making a capacitive water level application using FDC1004, with three sensors (Liquid level sensor, environmental ref sensor and liquid ref sensor)

I2c communication is running well, i can initialize and read registres. But i'm facing two problems :

1/ The measures i read are very instable

2/ the CSL and CRL measures are at the same value regardless the level of liquid in my container.

the fdc register configuration is single ended (measurement between CINn and GND).

Using the formula Cap=CINn_two complement/2e19, i have capacitances for all sensor around 24.

Is there something i've missed ?

Thanks a lot if you could help.

Best regards.

Hervé MAZIERE (from France)

  • 0
    TI__Genius 17440 points

    Hello Hervé,

    Can you clarify what the CSL and CRL sensors are? Is this the liquid level sensor and the liquid reference sensor?

    Are you using the CAPDAC? What are CHA and CHB for each measurement?

    Finally, are you using the out-of-phase method or the traditional liquid level sensing method?

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 40 points

    Hi Kristin,

    Thanks a lot for your quick reply !

    I'm using the same shematical as in doc fdc1004.pdf, (typical application, page 1 or 21)

    So yes, CSL is for liquid level sensor, CRL suits for liquid reference sensor.

    I tried severals configurations, but the last is :

    CONF_MEAS1 : CIN1 on CHA, no capdac (0x1C00)

    CONF_MEAS2 : CIN2 on CHA, no capdac (0x3C00)

    CONF_MEAS3 : CIN3 on CHA, no capdac (0x5C00) // not use

    CONF_MEAS4 : CIN4 on CHA, capdac use (0x70F0)

    FDC configuration : 0x8400

    All the three measures are evolving depending the water level, that's what i see. It's ok for the liquid level sensor, but not for environmental and liquid ref sensors.

    See below some CAD recorded at different levels.

    CSL CRL CRE
    liquid level at 0%
    3845975 3846833 3846361
    3835504 3834623 3835631
    3834167 3833985 3834196
    liquid level at 80%
    4218174 4218137 4219910
    4218555 4217803 4219688
    4218263 4219253 4217597
    liquid level at 50%
    4052444 4052893 4053326
    4054360 4054068 4053513
    4054911 4054281 4054973
    liquid level at 20%
    3915839 3915390 3915572
    3915216 3915216 3915071
    3915752 3914338 3915273
  • 0 in reply to MAZIERE Herve
    Prodigy 40 points

    Hi Kristin,

    I've made others measurement with one configuration change:

    CONF_MEAS4 : CIN4 on CHA, no capdac use (0x7C00), to have the same conf as the others CIN.

    I do the CAD sequentially of CIN1/ CIN2 / CIN4. I've tried CIN2 / CIN4 /CIN1 and have the same results even in run mode or step by step mode.

    I understand that normally, the CAD values of the reference sensors (CRL and CRE) do not change.

    If you need more informations, do not hesitate to contact me.

    Thanks a lot.

    Best regards.

    Hervé MAZIERE

  • 0 in reply to MAZIERE Herve
    Prodigy 40 points
    Dear all, it's ok for now, I've just resolved my problem.