SI Traceable Primary Calibration of In-Line Conductivity Sensors
By Steffen Seitz, Ph.D., Petra Spitzer, Pascal Rajagopalan, and Daniel Darbouret, Ph.D.
Currently, conductivity measurement devices for application in pure and high-purity water are usually calibrated with respect to standard solutions having conductivities orders in magnitude larger than the actual application�s range of the sensors. Without independent reference standards in the range of application, it is not possible to determine the measurement error of the indicated conductivity value. In this article, we present a new calibration method that resolves this shortcoming. In a closed (high-purity) water circuit, in which the conductivity value can be adjusted, conductivity is measured with a primary method traceable to the Syst�me International d'Unit�s (SI). We present calibration data of a conductivity measurement cell over a measurement range from the high-purity water level up to 15 microsiemens per centimeter-1 (�S cm1). We demonstrate that a measurement error of up to 25% could occur, if the resistance measurement of the meter is not adapted to the characteristics of the cell.
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