METHOD FOR DETERMINING THE CONDUCTIVITY OF A MEDIUM

Abstract

The present disclosure relates to a method for determining the conductivity of a medium by means of a conductive conductivity sensor, comprising the steps of determining measured values of the conductivity sensor, determining reference measured values of a reference circuit integrated into the conductivity sensor, deriving at least one adjustment value from the reference measured values of the reference circuit, and correcting the measured values of the conductivity sensor by means of the at least one adjustment value.

Claims

1. A method for determining the conductivity of a medium by means of a conductive conductivity sensor, comprising the steps: determining measured values of the conductivity sensor; determining reference measured values of a reference circuit integrated into the conductivity sensor; deriving at least one adjustment value from the reference measured values of the reference circuit; and correcting the measured values of the conductivity sensor by means of the at least one adjustment value.

2. The method according to claim 1, further comprising: alternating between determining the measured values of the conductivity sensor and determining the reference measured values of the reference circuit in a time-controlled manner.

3. The method according to claim 2, further comprising: determining two measured values of the conductivity sensor and subsequently determining one reference measured value of the reference circuit.

4. The method according to claim 1, wherein the conductivity sensor includes an electronic component with at least two measurement ranges including an active measuring range, and the method further comprises: during a measurement, adjusting the active measuring range more frequently than the other measurement ranges.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The described embodiments and other features, advantages and disclosures contained herein, and the manner of attaining them, will become apparent and the present disclosure will be better understood by reference to the following description of various exemplary embodiments of the present disclosure taken in conjunction with the accompanying drawings, wherein:

[0013] FIG. 1 shows a measuring circuit for measuring conductivity with an integrated reference circuit according to exemplary embodiments of the present disclosure.

[0014] FIG. 2 depicts a sequence of medium and adjustment measurements according to exemplary embodiments of the present disclosure.

[0015] FIG. 3 depicts a sequence of medium and adjustment measurements in various measurement ranges according to exemplary embodiments of the present disclosure.

[0016] Like reference numerals indicate the same or similar parts throughout the several figures. It should be appreciated that not all of the features of the components of the figures are necessarily described. Some of these non-discussed features, such as various fasteners, etc., as well as discussed features are inherent from the figures. Other non-discussed features may be inherent in component geometry or configuration.

DETAILED DESCRIPTION

[0017] FIG. 1 shows a measuring circuit 3 for measuring conductivity with an integrated reference circuit. The measuring circuit 3 is operated by means of a signal generator (not shown) that provides a signal S.sub.f with a frequency f. A generator amplifier VG amplifies the signal S.sub.f and generates an adjustment current I.sub.adj. The adjustment current I.sub.adj flows through a shunt resistor R.sub.shunt and generates a shunt voltage U.sub.shunt. If the shunt voltage U.sub.shunt and the shunt resistor R.sub.shunt are known, the adjustment current I.sub.adj can be determined:

[00001]$I_{\mathrm{adj}.}=\frac{U_{\mathrm{shunt}}}{R_{\mathrm{shunt}}}$

[0018] Through the shunt resistor R.sub.shunt, the adjustment current I.sub.adj flows to a multiplexer MUX that comprises two switches S.sub.1 and S.sub.2. Both switches S.sub.1, S.sub.2 comprise three positions and are synchronized, which means that if the top switch S.sub.1 is in the center position, the bottom switch S.sub.2 is also in the center position, etc. Connected to the MUX are voltage dividers, one voltage divider including the resistors R.sub.1 and R.sub.p1, the other voltage divider including the resistors R.sub.2 and R.sub.p2. If both switches S.sub.1, S.sub.2 are in the center position, the adjustment current I.sub.adj flows through voltage divider R.sub.1 and R.sub.p1 via a third closed switch S.sub.3 to ground and generates a voltage U.sub.Rpx along R.sub.p1:

U.sub.R.sub.px=R.sub.p1.Math.I.sub.adj.

[0019] The voltage U.sub.Rpx is amplified by means of an amplifier V, wherein the amplification factor v is determined as follows:

[00002]$v=\frac{U_{\mathrm{adj}.}}{U_{R_{\mathrm{px}}}}$

[0020] If the resistors R.sub.shunt and R.sub.p1 are dimensioned as follows:

R.sub.shunt=100 R.sub.p1=390 ,

and if, for example, the following values are measured for the shunt voltage U.sub.shunt and the adjustment voltage U.sub.adj:

U.sub.shunt=100 MV U.sub.adj=2 V,

then the result for I.sub.adj, U.sub.Rpx, and v is:

[00003]$I_{\mathrm{adj}.}=\frac{U_{\mathrm{shunt}}}{R_{\mathrm{shunt}}}=\frac{100.Math..Math.\mathrm{mV}}{100.Math..Math.}=1.Math..Math.\mathrm{mA}$$U_{R_{\mathrm{px}}}=R_{p.Math..Math.1}.Math.I_{\mathrm{adj}.}=390.Math..Math..Math.1.Math..Math.\mathrm{mA}=390.Math..Math.\mathrm{mV}$$v=\frac{2.Math..Math.V}{0.39.Math..Math.V}=\underset{\_}{5.128}$

[0021] If both switches of the multiplexer MUX are in the top position, the adjustment current I.sub.adj flows via two current electrodes I+, I through the medium, and a measured value of the conductivity sensor is determined. The current electrodes I+ and I, together with the two voltage electrodes U+, U, constitute the four poles of the four-terminal measurement of the conductivity sensor. During the measurement of the medium, the switch S.sub.3 is open and connected to a separate ground, so that the voltage electrode U is not short-circuited with the current electrode I.

[0022] If the medium between the voltage electrodes U+ and U is represented by a medium resistance R.sub.m, the voltage U.sub.m between the voltage electrodes U+ and U decreases. The current I.sub.m (not shown in the drawing) is regulated until the current I.sub.m through the medium is equal to the adjustment current I.sub.adj (see above). In this example, the following values were measured for the shunt voltage U.sub.shunt and the adjustment voltage U.sub.adj, after the switches were changed from the center to the top position:

U.sub.shunt=80 mV U.sub.adj=1 V

[0023] Thus, the medium resistance R.sub.m can be determined as follows, by means of the amplification factor v=5.128:

[00004]$I_m=\frac{U_{\mathrm{shunt}}}{R_{\mathrm{shunt}}}=\frac{80.Math..Math.\mathrm{mV}}{100.Math..Math.}=0.8.Math..Math.\mathrm{mA}$$U_m=\frac{U_{\mathrm{adj}.}}{v}=\frac{1.Math..Math.V}{5.128}=195.Math..Math.\mathrm{mV}$$R_m=\frac{U_m}{I_m}=\frac{0.195.Math..Math.V}{0.8.Math..Math.\mathrm{mA}}=\underset{\_}{243.76.Math..Math.}$

[0024] With an on-board adjustment, the conditions are, therefore, adjusted exactly in the same way as they are adjusted in a medium measurement (amplitude, frequency, shunt resistor, amplification). The goal of the adjustment is the calculation of the amplification factor v of the amplifier V. With the adjustment current I.sub.adj, the ideal voltage drop U.sub.Rpx through the resistor R.sub.p1 can be calculated. With the measured adjustment voltage U.sub.adj, the amplification factor v can be calculated. The amplification factor v compensates for all errors of the measuring circuit 3. If the current flow is subsequently directed through the medium again, the same conditions prevail as during the adjustment of the measurement range. However, the current flow is corrected or adjusted by means of the determined amplification factor v.

[0025] FIG. 2 shows a sequence of medium and adjustment measurements. The medium and adjustment measurements each last for half a second and occur once per second each. One adjustment measurement follows two medium measurements.

[0026] FIG. 3 shows a sequence of medium and adjustment measurements in accordance with FIG. 2, in which the medium and adjustment measurements occur in different measurement ranges 0, 1, and 2. The measurement range 0, in which the current conductivity measurement occurs, is adjusted more frequently than the measurement ranges 1 and 2. If the measurement range is changed from 0 to 1, the adjustment values for measurement range 1 are available and can be provided immediately, in order to ensure optimal measurement performance.