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LDC1101: LDC1101

Part Number: LDC1101
Other Parts Discussed in Thread: TIDA-00317

Hi,

My customer is looking for a way to measure the distance of a float in a tube to measure the liquid level.

The range is 5-7 cm and they need an accuracy of 0.1%

I was thinking of inductive or capacitive sensing using LDC of FDC devices.

SInce the electronics are inside float, battery powered it has to be low power.

There are 2 measurements per second.

Can you propose what would be usable solutions?

They are also very interested in the drift over time of LDC / FDC systems.

Do we have any papers on that topic?

  • Hello,

    Can you provide a picture of the setup? Typically the electronics go on the outside of the container and measure either the liquid directly or if the float has a metallic coating/surface to measure that. If the electronics are inside the float then for an inductive sensor you would need to have the wall of the tube containing a piece of metal with a gradient, similar to figure 1 of the following application note on linear position sensing: http://www.ti.com/lit/pdf/SNOA931

    One of the main challenges I see with this approach is that the float should not be able to rotate so that it can maintain a constant distance between the metal surface and the sensor. I suspect that this will be challenging however. Also, given the power consumption requirement you will need to put LDC1101 in sleep or shutdown mode for most of the time and wake it up with a lower power MCU to take the measurement. We can achieve low power this way especially with the LDC1101 which has a SPI interface and fast conversion interval which allows for very quick duty cycle. You can refer to the following application note on power reduction techniques for more information: http://www.ti.com/lit/pdf/SNOA949

    If it is possible to leave the electronics on the outside of the tube that would be preferable though. You could measure the float or the liquid directly with a capacitive sensor, similar to our liquid level sensing reference design: http://www.ti.com/tool/tida-00317

    For a list of our inductive and capacitive sensing application notes, see below:

    • http://www.ti.com/sensing-products/inductive-sensing/technical-documents.html#
    • http://www.ti.com/sensing-products/capacitive-sensing/capacitance-to-digital-converters/technical-documents.html#

    Hopefully this helps point you in the right direction.

    Regards,

    Luke