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On-line Conductivity Monitoring and Analysis
Mettler Toledo conductivity probes are available in a variety of types to suit every process need.
Two electrode sensors
The two electrode sensor design provides for the classical measurement of conductivity. An AC voltage is applied across the two electrodes and the resistance between them is measured.
Two electrode sensors are ideal for measuring samples with very low conductivity including water conditioning and purification, Ultra Pure Water for power generation and Water for Injection for pharmaceutical applications. The high solution resistance and the ability to determine the cell constant to four decimal places allow for very high accuracy and precise measurements.
Four electrode sensors
The four electrode sensor design is an extension of the two electrode system. As with the two electrode sensor, an AC voltage is applied across the two outer electrodes. The voltage drop across the two inner electrodes is measured, eliminating polarization errors at high conductivity values and also maintaining accuracy despite minor fouling caused by coating of the electrode surface.
Inductive sensors
The inductive conductivity sensor consists of two toroidal coils that are encapsulated in a plastic body (normally PVDF or PEEK for chemical resistance). Since the electrodes are encapsulated they are not in contact with the process sample and as such the inductive sensors are highly resistant to fouling.
The measurement principle involves passing an AC voltage at 10kHz through one of the coils. This induces a magnetic field through the centre of the sensor which generates a current loop when placed in a conductive medium that is proportional to the conductivity of the medium. This induced current is then sensed by the second toroid.
This measurement principle allows for the measurement of very high conductivity samples. The encapsulation of the sensors not only allows for measurements in fouling and corrosive samples, and there are no polarization effects.
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