My name is Jenny, and I want to find out more about liquid analysis. For those like me, who do not have a background in technical studies, I use this section in each issue to explain in more detail a different “piece of the puzzle” of our huge area of expertise. In this issue: the four-electrode conductivity measurement.
If you need to measure conductivity across a wide measuring range using a single sensor, it’s safe to say that “four wins”. Only sensors with four electrodes deliver reliable measurement results spanning from low to high conductivity values. I’ll explain why this is the case in layman’s terms. As a start, sensors with four electrodes have two electrodes opposite one another. An alternating voltage is applied to these electrodes.
This ensures that positively and negatively charged ions are attracted to ions of the opposite charge, causing them to move toward each other. If the charge of the electrodes switches, the ions move back to where they started. A higher number of ions moving in a liquid results in higher conductivity. But if there are too many ions, they repel each other, thereby inhibiting movement to some extent. This distorts the conductivity measurement: the actual value would be higher than the measured value.
This is called the polarization effect. At this point in time, the four-electrode measurement gets interesting. In such measurements, the two additional electrodes act as observers. These two conductivity measurement watchmen keep a close eye on the polarization and report the deviation between the measured and actual values to the transmitter. Then, the corrected (and correct) measured value is output from the transmitter, and this compensates for the polarization effect.
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Jan Swart
Product Manager: Analytics
