Method and device for measuring the conductivity of a liquid, with which the influence of polarisation is counteracted

Claim 2

Method for measuring the conductivity of a liquid, in which two electrodes (2,3) are put in contact with the liquid and a block pulse (a) of voltage or current of predetermined polarity is applied to the electrodes, the current flowing between the electrodes or the voltage between the electrodes being sampled at different time points (t₁,t₂,t₃) during said block pulse, the conductivity of the liquid body between the electrodes being determined, characterized in that from at least three sample values, the conductivity of the liquid body between the electrodes is calculated, using the relation that in the period of the block pulse the proportion between current and voltage is approximately an exponential function.

Claim 3

Method according to claim 1, characterized in that the block pulse (a) is the positive or negative half of a rectangular a.c. voltage or current.

Claim 4

Method according to claim 1 or 2, characterized in that from the exponential function also the imaginary part of the impedance of the liquid between the electrodes is determined.

Claim 5

Method according to claim 1, 2 or 3, characterized in that the frequency of the a.c. voltage or current is increased with a higher value of the imaginary part or a greater difference between sample values at predetermined time points.

Claim 6

Method according to one or more of the preceding claims, characterized in that the a.c. voltage or current is symmetrical.

Claim 7

Device for measuring the conductivity of a liquid, provided with a source (1) of a block voltage or current (a), which source is connected to a circuit connectable to electrodes (2,3) contacting a liquid, a meter (4) for measuring the current or the voltage between the electrodes,a sampling device (6,7,8,9,10) adapted to sample repeatedly the current or the voltage value in a period of the block voltage or current and a processor which is connected to the sampling device for receiving and processing the sample values, characterized in that the processor is adapted to derive an exponential function from at least three sample values and to determine the resistance and the imaginary part of the impedance between the electrodes.

Claim 8

Device for measuring the conductivity of a liquid, provided with a source (1) of a block voltage or current (a), which source is connected to a circuit connectable to electrodes (2,3) contacting a liquid, a meter (4) for measuring the current or the voltage between the electrodes,a sampling device (6,7,8,9,10) adapted to sample repeatedly the current or the voltage value in a period of the block voltage or current and a processor which is connected to the sampling device for receiving and processing the sample values, characterized in that the processor is adapted to derive an exponential function from at least three sample values and to determine the resistance and the imaginary part of the impedance between the electrodes.

Claim 9

Device according to claim 6, characterized in that the frequency of the said source is adjustable and in that the processor is adapted to adjust said source to a higher frequency with a higher value of the said imaginary part of the impendance.