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FDC2214: liquid-level sensing

K.Hamamoto
Guru 12155 points
Part Number: FDC2214
Other Parts Discussed in Thread: FDC1004

Hi

Our customer are considering FDCxxxx device and refers the following application note which is SNOA935A.

http://www.tij.co.jp/jp/lit/an/snoa935a/snoa935a.pdf

In this case there are two sensors which is level sensor and reference sensor. Which does the configuration use at this case? (single-end? or differential?)

On the datasheet, there is mentioned an advantages of single and differential.

Which do you recommend, the single-end or differential at this application?


On the other hand, how should we shield the reference sensor at differential configuration if we use the refernce sensor?

(I think the common-mode noise might be ok but the different noise at the each sensor are affected.)

Regards,

Koji Hamamoto 

  • 0
    TI__Genius 13335 points
    Hello,
    If using the FDC221x for liquid level as SNOA935A shows then a differential setup is recommended. Figure 2 of SNOA935A shows the level sensor connected to IN0A and IN0B while the reference sensor is connected to IN1A and IN1B for a total of 4 electrodes and 2 differential measurements.
    If using the FDC221x there is no inherent shield driver like the FDC1004. If you add a shield to the system it should be a ground plane on top of the sensors facing the external environment. However, this will significantly reduce the sensitivity especially if there is not much distance between the sensors and ground plane. You may also used a hatched pattern for the ground pour instead of a solid pour which will reduce the amount of capacitance formed between the sensor and ground to improve sensitivity.
    Regards,
    Luke
  • 0 in reply to Luke LaPointe
    Guru 12155 points

    Hi Luke,

    Thank you for your support.

    >If using the FDC221x for liquid level as SNOA935A shows then a differential setup is recommended. Figure 2 of SNOA935A shows the level sensor connected to IN0A and IN0B while the reference sensor is connected to IN1A and IN1B for a total of 4 electrodes and 2 differential measurements.

     At Figure 2 of SNOA935A , it looks 4 electrodes and 2 single end measurements such as the following configuration.

    4 electrodes means that 2 electrodes are positive and other 2 electrodes are ground. So that, there are two sensors. Is that correct?


    On the other hand, which do you recommend at the following application such as Proximity Sensing? (single-end? or differential?)

    (Which does it applied either of single-end or differential at the following design?) 

    http://www.tij.co.jp/product/jp/FDC2214/support#videoheader

    Regards,

    Koji Hamamoto

  • 0 in reply to K.Hamamoto
    TI__Genius 13335 points

    Hello,

    I have annotated figure 2 to be more clear:

    For a proximity sensing application, typically single ended is better because you can get a larger sensor area. You can refer to the following application note about proximity sensing using the FDC221x: www.ti.com/.../SNOA940

    Regards,

    Luke

  • 0 in reply to Luke LaPointe
    Guru 12155 points
    Hi Luke,

    Thank you!

    Regards,
    Koji Hamamoto