Method for monitoring the quality of electrochemical measuring sensors and a measuring arrangement with an electrochemical measuring sensor

• US 20020027085A1
• Filed: 04/03/2001
• Published: 03/07/2002
• Est. Priority Date: 04/04/2000
• Status: Abandoned Application

• Current Assignee: Metrohm AG (Metrohm Stiftung)
• Original Assignee: Metrohm AG (Metrohm Stiftung)
• Inventors: Kiser, Gerhard, Stori, Roland
• Application Number:
  US09/823,989
• Publication Number:
  US 20020027085A1
• Time in Patent Office: Days
• US Class Current: 205/775
• CPC Class Codes: G01N 27/286 Power or signal connectors associated therewith
• CPC Class Codes: G01N 27/4165 for pH meters

Abstract

The quality of electrochemical measuring sensors with at least one measuring electrode, for example pH-sensors is checked in that the frequency response of the sensor impedance is measured over a frequency range (f₁, f₂). The frequency response or the value of an equivalent circuit diagram of the measuring circuit (1) computed from the frequency response are compared to reference values. Deviations from the reference values indicate an impairment or damage of the measuring electrode (2). Simultaneously proceeding from the membrane impedance the temperature (T) of the measuring electrode (2) and thus of the measuring fluid (F) is determined.

Claims

1. A method for monitoring electrochemical measuring sensors having at least one measuring electrode, such as pH-sensors, the method comprising the steps of

measuring a frequency response Z(f), Φ

(f) of the sensor impedance over a predetermined frequency range whereby frequency response values are generated and

comparing said frequency response values to first reference values.

2. A method according to claim 1, wherein said frequency range is 0.1 Hz to 10 kHz.

3. A method according to claim 1, comprising the further steps of determining values (R_glass, C_glass, W_glass, R_cable, R_ref, C_ref, C_cable) of elements of an equivalent circuit describing the measuring sensor on the basis of said frequency response values the and

comparing said values of said elements to second reference values.

4. A method according to one of the claims 1 to 3, wherein a sensor signal is measured and evaluated simultaneously to determining said frequency response.

5. A method according to claim 1, comprising the further steps of determining the temperature (T) of the measuring electrode and thus the temperature (T) of a fluid (F) to be measured based on the sensor impedance (Z), in particular based on the frequency response.

6. A method according to claim 5, using a pH-electrode wherein the electrical resistance R_glass of the membrane of the electrode is determined and wherein said temperature is determined based on said electrical resistance.

7. A method according to claim 1, comprising the further step of transferring a sensor signal and signals defining the frequency response via a serial interface to a control apparatus.

8. A method according to claim 1, comprising the further step of producing a warning signal as soon as a deviation between said frequency response values or values computed from said frequency response and said reference values lies outside a predeterminable tolerance region.

9. A method according to claim 1, wherein said frequency range is selected in a manner such that there occurs no polarisation of the measuring electrode.

10. A measuring arrangement with an electrochemical measuring sensor comprising at least one measuring electrode, such as a pH-sensor, and an evaluation arrangement

wherein in the evaluation arrangement there are stored reference values of the frequency response of the sensor impedance and/or reference values of an elements of the equivalent circuit of the measuring sensor computed therefrom.

11. A measuring arrangement according to claim 10, wherein the evaluation arrangement has an integrated circuit.

12. An arrangement according to claim 11, wherein said integrated circui is arranged on the measuring electrode.

13. A measuring arrangement according to claim 10, wherein said evaluation unit has a control and display apparatus which galvanically is separated from the sensor and preferably from the integrated ciruit.

14. A measuring arrangement according to claim 10, wherein the measuring arrangement is provided with a temperature sensor.