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Liquid Level Sensing with the Immersive Straw Approach with FDC

ttd
Mastermind 8660 points
Other Parts Discussed in Thread: FDC1004, FDC2214

Dear Technical Support Team,

 

I have some questions about Liquid Level Sensing with the Immersive Straw Approach with FDC.

 

1.)

How is the distance between INNER TUBE and OUTER TUBE?

 

http://www.tij.co.jp/jp/lit/an/snoa934/snoa934.pdf

 


2.)

Shielded cable length is different between REFERENCE and SENSOR.

REFERENCE shielded cable lenght is longer than SENSOR. 

Dose it affect little error of liquid level sensing?

 

3.)

Which do recommend FDC1004 or FDC2214 for Liquid Level Sensing with the Immersive Straw Approach?

Could you tell me difference between them for this Liquid Level Sensing?

 

Best Regards,

y.i

  • 0
    TI__Expert 6480 points
    Hi y.i,

    1.) Unfortunately, I'm not sure what the distance is between the inner and outer tube for this particular design.
    2.) This should have little affect on the measurements.
    3.) If active shielding is needed, the FDC1004 is a better choice. Otherwise, the FDC2214 will have better performance.

    Thanks,
    Rachel
  • 0 in reply to Rachel Liao
    Mastermind 8660 points
    Hi Rachel,

    Thank you for your reply.
    I insert following my commnet.

    >2.) This should have little affect on the measurements.
    ⇒It's better to adjust the shielded cable length between sensor and reference.
    So I will try it.

    Best Regards,
    y.i
  • 0 in reply to ttd
    Intellectual 980 points

    The distance between the outer and inner tube should be maximized as possible. What happens is that if the outer tube is right up against the sensors with no shielding, the dielectric material of the tube will enhance the sensitivity of the sensors. If there is some kind of disturbance in the capacitance on the backside of the sensors, then it could possibly pick up that disturbance. With the outer tube at a certain distance away, the air insulation will minimize the sensitivity of the backside of the sensors (if there is no shielding). The distance away will have to be determined by trial and error based on how large your sensors are, but there is a point at which increasing the distance more will not have a noticeable effect.

    also, the outer tube material can be anything. You just need to make sure the sensors are isolated from the liquid since direct contact will short the connections and be ineffective at measuring any capacitance. The best thing that we had at the moment was acrylic tubes, but potting or epoxy compound can be used as a permanent solution and should work.