APPARATUS FOR MEASURING THE ELECTRICAL CONDUCTIVITY OF A LIQUID MEDIUM

• US 20140152332A1
• Filed: 06/26/2012
• Published: 06/05/2014
• Est. Priority Date: 07/20/2011
• Status: Active Grant

• Current Assignee: OPTEK-Danulat GmbH
• Original Assignee: OPTEK-Danulat GmbH
• Inventors: Platte, Daniel, Pohl, Afred
• Granted Patent: US 9,354,193 B2
• Time in Patent Office: Days
• US Class Current: 324/713
• CPC Class Codes: G01N 27/06 of a liquid involving electrolysis G01N27/26
• CPC Class Codes: G01N 27/07 Construction of measuring vessels; Electrodes therefor

Abstract

Device for measuring electrical conductivity of a liquid medium comprising constant voltage means, connected to a first electrode arrangement for injecting an alternating signal into the liquid medium, detection means, connected to a second electrode arrangement coupled via the liquid medium, for generating a measurement signal influenced by the electrical conductivity with a clock frequency (CLK) of the alternating signal, and evaluation means which from a current-proportional injection signal of the current injected by the first electrode arrangement into the liquid medium and from the measurement signal generate a conductivity signal of the liquid medium. The constant voltage means are made in an individual circuit branch which has commutator means for the first electrode arrangement and ohmic resistance means in a series connection, the current-proportional injection signal being tapped as a voltage drop over the resistance means.

Claims

1. A device for measuring electrical conductivity of a liquid medium, comprising:

constant voltage means connected to a first electrode arrangement for injecting an alternating signal into the liquid medium,

detection means connected to a second electrode arrangement, which is separated from the first electrode arrangement and which is coupled via the liquid medium, said detection means generating a measurement signal (U(U)) influenced by the electrical conductivity with a clock frequency (CLK) of the alternating signal, and

evaluation means, which from a current-proportional injection signal (U(I)) of the current injected by the first electrode arrangement into the liquid medium and from the measurement signal (U(U)), generate an output signal, and make it available for further electronic processing,

wherein

the constant voltage means are made in an individual circuit branch which has commutator means for the first electrode arrangement and ohmic resistance means in a series connection, and

the current-proportional injection signal (U(I)) being tapped as a voltage drop over the resistance means.

2. The device as claimed in claim 1, wherein a separate first analog-digital converter unit for generating the digital current-proportional injection signal (AD(U(I))) which is not integrated into the evaluation means is assigned to the resistance means.

3. The device as claimed in claim 1, wherein a separate second analog-digital converter unit for generating the digital measurement signal (AD(U(U))) which is not integrated into the evaluation means is assigned to capacitance means which interact with the second electrode arrangement.

4. The device as claimed in claim 2, wherein the first analog-digital converter unit generates a serial output signal for the evaluation means and interacts with them via a serial connecting line which is assigned to the first analog digital converter unit.

5. The device as claimed in claim 2, wherein the first analog-digital converter unit has integrated filter means tuned to the clock frequency of the alternating signals and/or of a supply voltage signal.

6. The device as claimed in claim 2, wherein a common voltage supply unit is assigned to the first analog-digital converter unit and is used in addition as a supply voltage unit for the constant voltage means and/or is integrated into them and/or the first analog-digital converter unit has a common reference voltage source for converter quantization.

7. The device as claimed in claim 1, wherein the constant voltage means have an analog control unit and/or are implemented without integrated digital circuit modules.

8. The device as claimed in claim 1, wherein the device further comprises temperature detection means which are made for interaction with the liquid medium and which interact with the evaluation means via an assigned third analog-digital converter unit such that the temperature of a medium influences the conductivity signal.

9. The device as claimed in claim 1, wherein the individual circuit branch is made such that the ohmic resistance means are set up to be invariable, free of hysteresis and not able to be discretely switched over or selected,

and/or there are not active and/or switching elements in the circuit branch which influence the ohmic resistance value.

10. The device as claimed in claim 1, wherein the detection means have capacitor means whose capacitor voltage determines the digital measurement signal which is generated continuously and/or independently of the clock frequency of the alternating signal.

11. The device as claimed in claim 1, wherein the measurement signal (U(U)) is present parallel and synchronously on a first and a second input of the detection means with signal levels which have been amplified to different degrees from one another.

12. The device as claimed in claim 1, wherein a repetition frequency and/or cycle frequency of the generation of the digital current-proportional injection signal and/or of the digital measurement signal is set up to the clock frequency of the alternating signal in a ratio of less than 1:

100.

13. The device as claimed in claim 1, wherein the device further comprises decoupling means between respective electrodes of the second electrode arrangement and commutator means which are connected downstream of them.

15. A device as claimed in claim 1, wherein the liquid medium is an aqueous medium.

16. A device as claimed in claim 1, wherein the second electrode arrangement is an electrode pair.

17. A device as claimed in claim 1, wherein the detection means are coupled via the liquid medium in the manner of a four-pole configuration.

18. A device as claimed in claim 1, wherein the output signal is a conductivity signal of the liquid medium.

19. A device as claimed in claim 1, wherein the current-proportional injection signal is tapped as a voltage drop over a partial resistor of the resistance means.

20. The device as claimed in claim 3, wherein the second analog-digital converter unit generates a serial output signal for the evaluation means and interacts with them via a serial connecting line, which is assigned individually to the second analog-digital converter unit.

21. The device as claimed in claim 3, wherein the second analog-digital converter unit has integrated filter means tuned to the clock frequency of the alternating signals and/or of a supply voltage signal.

22. The device as claimed in claim 3, wherein a common voltage supply unit is assigned to the second analog-digital converter unit and is used in addition as a supply voltage unit for the constant voltage means and/or is integrated into them and/or the second analog-digital converter unit has a common reference voltage source for converter quantization.

23. The device as claimed in claim 2, wherein a separate second analog-digital converter unit for generating the digital measurement signal (AD(U(U))) which is not integrated into the evaluation means is assigned to capacitance means which interact with the second electrode arrangement.

24. The device as claimed in claim 23, wherein the first and/or the second analog-digital converter unit generates a serial output signal for the evaluation means and interacts with them via a serial connecting line, especially via a serial connecting line which is assigned individually to each of the first and second analog-digital converter units.

25. The device as claimed in claim 23, wherein the first and/or the second analog-digital converter unit has integrated filter means tuned to the clock frequency of the alternating signals and/or of a supply voltage signal.

26. The device as claimed in claim 23, wherein a common voltage supply unit is assigned to the first and/or the second analog-digital converter unit and is used preferably in addition as a supply voltage unit for the constant voltage means and/or is integrated into them and/or the first and/or the second analog-digital converter unit has a common reference voltage source for converter quantization.

27. The device as claimed in claim 9, wherein the ohmic resistance means are constant with their ohmic resistance value.

28. The device as claimed in claim 12, wherein the ratio is less than 1:

500.

29. The device as claimed in claim 13, wherein the decoupling means is ohmic resistance means.

14. A use of a device for measuring electrical conductivity of a liquid medium, comprising:

constant voltage means connected to a first electrode arrangement for injecting an alternating signal into the liquid medium,

detection means connected to a second electrode arrangement, which is separated from the first electrode arrangement and which is coupled via the liquid medium, said detection means generating a measurement signal (U(U)) influenced by the electrical conductivity with a clock frequency (CLK) of the alternating signal, and

evaluation means, which from a current-proportional injection signal (U(I)) of the current injected by the first electrode arrangement into the liquid medium and from the measurement signal (U(U)), generate a conductivity signal of the liquid medium, and make it available for further electronic processing,

wherein the constant voltage means are made in an individual circuit branch which has commutator means for the first electrode arrangement and ohmic resistance means in a series connection, and the current-proportional injection signal (U(I)) being tapped as a voltage drop over the resistance means, and

wherein the conductivity signal has an uninterrupted range of conductivity between 0.001 mS/cm and 1000 mS/cm.

30. The use as claimed in claim 14, wherein the liquid medium is water.

31. The use as claimed in claim 14, wherein the conductivity signal has the uninterrupted range of conductivity between 0.001 mS/cm and 850 mS/cm.