Integrable conductivity measuring device

Electricity: measuring and testing – Electrolyte properties – Using a conductivity determining device

Patent

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Details

Other Related Categories

324439, 324446, 324715, G01N 2706

Type

Patent

Status

active

Patent number

055437176

Description

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to an integrable conductivity measuring device for measuring the electric conductivity of liquids with a current source device which is connected to two current electrodes, over which a current with a rectangular waveform can be fed to the liquid, and with a measuring circuit is connected to two voltage electrodes for determining the voltage drop between the two voltage electrodes, which is dependent on the electric conductivity of the investigated liquid.
For determining the electric conductivity of a liquid, it is general knowledge to impress a current into a liquid and to measure the voltage drop therein which is inversely proportional to the conductivity of the liquid.
In the simplest version only two electrodes are used. The current is impressed in the liquid via these two electrodes and simultaneously the voltage drop is measured by these two electrodes. On this occasion so-called polarization effects occur which distort the actual measuring signal. These effects always occur when current flows over a boundary layer between an electrode and an electrolyte. Since a flow of current in an electrolyte is connected with ion migration, ions of one charge-type accumulate at the boundary layer between the electrolyte and the electrode weakening the original field and reducing the measuring signal.
In order to eliminate this disadvantage, conductivity measuring devices with a so-called four-electrode-arrangement are used, wherein a current source with two current electrodes is provided for impressing the measuring current. Two further electrodes, which can be considered as voltage electrodes, serve for measuring the voltage drop via the liquid. The voltage drop measured by the voltage electrodes is amplified by a downstream high-resistance amplifier. On account of the high input impedance of the amplifiers, the current flowing via the voltage electrodes can be kept small, so that in this measuring method the polarization effects can be reduced, on account whereof an improved measuring accuracy is achieved as compared to the conductivity measurement by way of only two electrodes. However, also in the four-electrode-arrangement the measuring current flowing via the voltage electrodes leads to a polarization and consequently to a distortion of the measuring signal.
From U.S. Pat. No. 4,656,427 a conductivity measuring device of the afore-mentioned kind is already known, working with a four-electrode-arrangement. Two current electrodes can be charged with a current having a rectangular waveform. Two voltage electrodes provided with downstream capacitors for separating dc potentials serve to detect the dynamic change in potential on account of the rectangular alternating current impressed in the liquid to be measured. This signal is amplified by a subsequent evaluation circuit, provided with an additional capacitor connected in series, for separating offset-currents, and is displayed after analog-to-digital conversion on a display unit.
It is furthermore known in conductivity measuring devices of the afore-described type to produce the impressed current as sinusoidal alternating current in order to prevent decomposition processes in the liquid by this measure, which would occur in the case of a measurement with impressed direct current.
Proceeding from the above-mentioned prior art the present invention is based on the object of further developing a conductivity measuring device of the afore-mentioned kind so that an improved measuring accuracy is obtained.
According to the invention this object is achieved by an integrable conductivity measuring device for measuring the electric conductivity of liquids, comprising a current source device connectable to two current electrodes via which a current with a rectangular waveform can be fed into the liquid, and a measuring circuit connected to two voltage electrodes for determining the voltage drop between the voltage electrodes which is dependent on the electric conductivity of the investigated liquid, wherein the measuring circuit is a swi

REFERENCES:
patent: 3495164 (1970-02-01), Dauphinee
patent: 3757205 (1973-09-01), Dauphinee
patent: 4656427 (1987-04-01), Dauphinee
patent: 4833413 (1989-05-01), Head
patent: 4988952 (1991-01-01), Seuastopoulus
patent: 5142238 (1992-08-01), White

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