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Measure Fluid Conductivity

Fred Zillinger
Prodigy 10 points

I need to measure the conductivity of water.

One way conductivity can be measured is with a toroidal coil placed in the water. The water forms a transformer winding around the toroid. I assume the LDC1000 could easily sense the conductivity of the water in this way.

My challenge is that the water I am measuring is at very high pressure.

The resolution of the LDC1000 attracts me. Is there a way to measure the conductivity of the water inside a small stainless tube? I can see using a ceramic tube but that has some safety issues.

  • 0
    TI__Genius 13650 points

    Hello Fred,

    Yes, the LDC can measure water conductivity if a toroid coil is placed inside a tube, provided that it doesn't cause any electrical shorts. It can also measure conductivity if the tube is made out of non-conductive material.

    Sensing through a tube of stainless steel is more difficult. Please refer to the question What are the general guidelines for sensing a target through metal? on our FAQ.

  • 0 in reply to Ben Kasemsadeh
    TI__Genius 13650 points

    Hello Fred,

    I need to correct my last statement; toroid coils are actually a bad coil choice for inductive sensing because they do not emit magnetic fields to the outside. A coil choice that emits a magnetic field is required.

    I should also point out that the skin depth of water is millions times higher than the skin depth of metals. The size of the coil should be in the order of twice the skin depth to achieve good resolution. Therefore, required coil size and water volume are very high.

    For example, to sense conductivity of sea water with inductive sensing, a coil with a minimum of 10cm diameter and 5MHz oscillation frequency is required. Even larger coils are required to achieve good resolution or to detect water with lower conductivity,