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Whether ultrasonic fluid level sensing can work with fluid in dual layer container having air/vaccum between both?

Perry Garg
Intellectual 340 points

In introductory videos, It is mentioned that ultrasonic fluid level sensing can work with Plastic, Metal and glass containers and single layer are used in videos, hence between water and transducer, only 1 single layer of container is there. My question is, If that metal container has 2 layers having air/vacuum between them, will same setup work? Thanks.

  • 0
    TI__Genius 16890 points
    Hi Perry,

    This could possibly work. The transducer would need to create a signal that is strong enough to go through the first layer, than the air, then the second layer, through the liquid being measured, reflected back and through all the layers on the way back. The signal will have to be strong, maybe even using a boosted drive like is used in the TDC1000-GASEVM eval board. The performance will heavily depend on how well the transducer is mounted. It is something you will need to try.

    Mike
  • 0 in reply to Michael Stout
    TI__Mastermind 21685 points
    It's better if there is a matching layer in-between to allow energy to move than vacuum or air (ultrasonic wave cannot travel in vacuum).

    www.nde-ed.org/.../hs_sound_index.php
  • 0 in reply to Michael Stout
    Intellectual 340 points

    Thanks, As you suggested using a strong signal, I guess there will be more than one echoes on RX on transducers because of multiple density changes in between due to layers. How we can filter all echos and find out which one is actual echo from water level, that we have to consider. Thanks. CC:

  • 0 in reply to Perry Garg
    TI__Genius 16890 points
    Hi Perry,

    I talked with someone who has tried this and he said the main problem is that all of the energy is lost in the double wall section of the container. There is very little energy that is actually available to create a reflection at the liquid/air interface. And then it needs to come back all the way back to the sensor. They can try it but the sensor will have to be driven very hard and it still most likely won't work.

    A way that has been used for double walled containers is to put the sensor inside the container mounted on the surface that contains the liquid.

    Mike
  • 0 in reply to Michael Stout
    Intellectual 340 points
    Hi , I am not sure that how the transducer will be placed in between 2 layers as both layers are sealed usually. Is there any other way around or seems like this tech. will not work for double wall containers? Thanks.
  • 0 in reply to Perry Garg
    TI__Genius 16890 points

    Hi Perry,

    The only way we have been able to make this work is by getting the sensor in between the two layers. 

    You can try putting the sensor on the outer surface and see if is works in your application.

    Would it be possible to put the sensor in the lid and measure from the lid down?


    Mike

  • 0 in reply to Michael Stout
    Intellectual 340 points

    , You suggesting to place the sensor on the upper lid of the container and then sense air distance instead of fluid level? Just to confirm.

  • 0 in reply to Perry Garg
    TI__Genius 16890 points
    Hi Perry,

    Yes, that is correct. A post explaining how to do this is here:

    e2e.ti.com/.../498792

    Mike
  • 0 in reply to Michael Stout
    Intellectual 340 points

    , I have read this post before. I have 2 concerns in this:This post says that from 17cm to 70cm distance can be sensed in this case.

    1. This post says that from 17cm to 70cm distance can be sensed in this case. But I have to sense distance from approx. 1cm to 20cm.

    2. This post says voltage required is 30v but we are planning to power it from approx. 3.3v max.

    Please let me know your views about these concerns. Thanks.

  • 0 in reply to Perry Garg
    TI__Genius 16890 points
    Hi Perry,

    Going through air has its own problems. Because the air is so absorptive it limits the distance. You are actually doing a shorter distance so you may be able to make it work.

    The BSTEVM board included with the GASEVM board has a boost converter to make the 30V.

    There are other problems, such as condensation on the sensor that can cause problems too.

    It is something you will have to try out, to see if it works for you.

    The best way is on the bottom of the container, but I don't see how you can do that unless you get the sensor in between the layers.

    Mike