De-Ionised Water Level Measurement challenges

Success or failure depends on how the measurement technology is able to accurately and reliably measure level, independent of conductivity variations. Water becomes "DI" (De-ionized) by having ions removed. This makes the water more pure, but it also removes the ions that give water its conductive nature.

All Radio Frequency (RF Admittance and RF Capacitance) level systems establish immunity to output signal changes with conductivity variations by driving the sensor to full "saturation". Saturation is the mathematical point where a sensor will have the ability to generate the entire signal that it is capable of generating, thus providing a stable, repeatable and linear output with level changes. As long as the sensor is in full "saturation" it will not be affected by variations in a liquids' conductivity.

* Saturation is achieved by a combination of probe capacitance and transmitter frequency.

* Low probe capacitance combined with low transmitter frequency provides the best combination for "saturation" on low conductivity liquids like DI water.

* DI Water conductivities can range from a low of about 1 - 2 microsiemens, up to about 10 - 15 microsiemens.
o To reliably measure liquids with conductivities in this range, an RF system must be able to "saturate" at this extremely low level of conductivity.

* Most RF level instrument manufacturers do not have systems with the ability to do this.

* The Drexelbrook RF Admittance and
Universal Lite systems have lower frequency options that permit reliable measurements with any liquid conductivity greater than 1 microsiemens.

If you have tried RF level systems on DI Water applications and liked the price, simple design and set-up, but have been left with a system that required frequent recalibration, or whose output signal would "drift" even when no DI Water was moved to or from the vessel, then try a Drexelbrook RF level system


June 2018


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