Electricity: measuring and testing – Electrolyte properties – Using a conductivity determining device
Patent
1994-11-14
1996-05-21
Wieder, Kenneth A.
Electricity: measuring and testing
Electrolyte properties
Using a conductivity determining device
324449, 324690, 257532, G01N 2706, G01R 2722
Patent
active
055193234
DESCRIPTION:
BRIEF SUMMARY
RELATED PATENT APPLICATION
Major aspects of the subject matter of this application are related to the subject matter of U.S. Ser. No. 08/119,243 pending corresponding to PCT/DE92/00242.
DESCRIPTION
The present invention refers to an integrable conductivity measuring device for measuring the electric conductivity of liquids.
For the purpose of determining the electric conductivity of a liquid, it is generally known to impress a current upon said liquid and to measure the voltage drop within said liquid, said voltage drop being inversely proportional to the conductivity of the liquid.
In the simplest case, only two electrodes are used for this purpose. The current is impressed upon the liquid via these two electrodes and, simultaneously, the voltage drop is measured by means of the same electrodes. On this occasion, so-called polarization effects occur, which distort the actual measuring signal. These effects occur whenever a current flows over a boundary layer between an electrode and an electrolyte. In view of the act that a flow of current in an electrolyte entails ion migration, ions of one type of charge will accumulate at the boundary layer between the electrolyte and the electrode, said ion accumulations weakening the original field and reducing the measuring signal.
In order to avoid this disadvantage, conductivity measuring devices with a socalled four-electrode arrangement are used, wherein a current source with two current electrodes is provided for impressing a measuring current. Two further electrodes, which can be referred to as voltage electrodes, serve to measure the voltage dropping across the liquid. The voltage drop, which is tapped by the voltage electrodes, is amplified by a high-ohmic amplifier connected downstream of said voltage electrodes. On account of the high input impedance of the amplifiers, the current flowing via the voltage electrodes can be kept small so that the polarization effects will be reduced when this measuring method is used, and this will result in an improved measuring accuracy in comparison with conductivity measurements making use of only two electrodes. However, also in the four-electrode arrangement the measuring current flowing via the voltage electrodes will cause a polarization and, consequently, a distortion of the measuring signal.
U.S. Pat. No. 4,656,427 already discloses a conductivity measuring device of the type mentioned at the beginning, which works with a four-electrode arrangement. Two current electrodes are adapted to be acted upon by a square-wave current. Two voltage electrodes, which are followed by capacitors for separating dc potentials, serve to detect the dynamic change in potential caused by the square-wave alternating current impressed upon the liquid to be measured. This signal is amplified by a subsequent evaluation circuit, which is provided with an additional capacitor connected in series and used for separating offset currents, and, after an analog-to-digital conversion, it is displayed on a display unit.
In conductivity measuring devices of the type described hereinbefore, it is also known to produce the impressed current as a sinusoidal alternating current so as to prevent by means of this measure decomposition processes in the liquid, which would occur if the measurement were carried out with an impressed direct current.
In order to eliminate these problems of the known integrable conductivity measuring devices comprising two voltage electrodes and two current electrodes, the prior, not-prepublished PCT/DE92/00242 (WO 92/18856) corresponding to U.S. Ser. No. 08/119,243 suggests that the current source device should produce a square-wave current which is supplied to the two current electrodes, and that the measuring circuit should be implemented as a switch-capacitor circuit provided with a measuring capacitor which is adapted to be coupled to and separated from the voltage electrodes via a switch means in time-dependence on the behaviour of the substantially square-wave current.
The measuring errors occurring due to polarizat
REFERENCES:
patent: 3495165 (1970-02-01), Dauphinee
patent: 3757205 (1973-09-01), Dauphinee
patent: 4010715 (1977-03-01), Robar
patent: 4656427 (1987-04-01), Dauphinee
patent: 4833413 (1989-05-01), Head
patent: 4931897 (1990-06-01), Tsukamoto et al.
patent: 4988952 (1991-01-01), Sevastopoulos et al.
patent: 5142238 (1992-08-01), White
patent: 5349494 (1994-09-01), Ando
Kordas Norbert
Manoli Yiannos
Do Diep
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Wieder Kenneth A.
LandOfFree
Integrable conductivity measuring device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Integrable conductivity measuring device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Integrable conductivity measuring device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2040862