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Thickness of container?

Shawn Hinzey
Prodigy 20 points

I was wondering.  How thick can the container be for the electrodes to live on the exterior of the vessel (as opposed to in direct contact with the liquid)?  I assume there is a max thickness for standard PVC before the signal degrades to unusable?  Much depends on what drives the DAC I suppose.

I'm trying to eliminate spurious readings due to "muck" buildup on the sensors themselves (if in the liquid).  I figure the container itself likely will be less prone to this (I hope), so mounting them on the exterior may be the better solution.

  • 0
    TI__Expert 7400 points
    Hi Shawn:

    Can you elaborate on your setup and liquid being sensed? What do you mean by muck buildup on the sensors itself?

    Typically the sensors are on the exterior of the container. The sensitivity or resolution you obtain is a function of the sensor dimensions (mainly width), liquid being sensed, and also the thickness and material of the container. It's best to try and minimize the distance between the sensors and liquid. The reason being is that most of the electric fields will be in the middle of the sensors. As you move further away, sensitivity decreases exponentially. Unfortunately there is no exact equation or calculation for max thickness since it is dependent on other parameters unknown. Typically containers that I have seen for various applications have thickness of a few mms and less than 1cm.

    Thanks
    David Wang
    Capacitive Sensing Applications
  • 0 in reply to David Wang11
    Prodigy 20 points

    Thanks for the reply!

    We'd be measuring in a relatively hostile marine environment so realize most times the tank(container) and anything inside of it (sensors) will get fouled over time (algae, scaling, etc.), which will change the reading slightly I'm sure.  Since your design is out-of-phase compensated, however, it should be able to account for most of this I surmise.  In any case, it's not clear what effect that would have on the reading, if any.  May be minimal.  I have used marine-grade cap. sensors before (on large tanks) but not at high resolutions; they worked fine.


    Have you guys ran any tests in a fairly fouled environment?

  • 0 in reply to Shawn Hinzey
    TI__Expert 7400 points

    If using the OOP, then with the shields on the backside, it will help protect the sensors itself significantly, but there will still be some fringing effects that may be noticeable. As far as the type of material or muck you would see in a marine environment on how it would affect measurements, it will effect it, but we don't know how much because it's dependent on the composition of the material. It also depends on what your resolution or accuracy requirements are, if it's less than <1% then you will probably see some effect, but if it's like 5% or 10%, you may be fine....

    We have not tested in fouled environments, but we do know the effects of it in different conditions like temp, humidity, rain, etc...

    Thanks

    -David Wang

    Capacitive Sensing Applications