Method of Checking the Function of a Sensor

• US 20060219575A1
• Filed: 03/20/2006
• Published: 10/05/2006
• Est. Priority Date: 04/01/2005
• Status: Active Grant

• Current Assignee: Mettler Toledo GmbH
• Original Assignee: Mettler Toledo GmbH
• Inventors: OBERLIN, Rene
• Granted Patent: US 7,691,254 B2
• Time in Patent Office: Days
• US Class Current: 205/775
• CPC Class Codes: G01N 27/404 Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid , e.g. Clark-type oxygen sensors
• CPC Class Codes: G01N 27/4163 checking the operation of, or calibrating, the measuring apparatus G01N27/3274, G01N27/4175 and G01N33/0006 take precedence

Abstract

The functioning of an amperometric electrochemical sensor having an electrochemical cell is monitored by the electrochemical cell. A perturbation quantity is imposed on the sensor, which is operated with voltage control at a given polarization voltage. The response to the perturbation is measured and a check value is calculated, using the response under the perturbation as an input value. The check value is compared to a system-dependent limit value. If the check value is larger than the system-dependent limit value, the initial polarization voltage is changed by a predefined voltage increment and the process is repeated, until an optimal polarization voltage has been found, i.e., until the calculated check value is smaller than the system-dependent limit value. A measuring system that serves to carry out the method is also described. An automated embodiment utilizes a computer-supported control- and processing-unit with a data memory and a data-evaluating program.

Claims

1. A method of checking the function of an amperometric electrochemical sensor which comprises an electrochemical cell, comprising the steps of:

a. applying a constant polarization voltage to the electrochemical cell, the first application of the constant polarization voltage being a constant initial polarization voltage;

b. applying a perturbation quantity to the electrochemical cell;

c. determining at least one response of the electrochemical cell in the presence of the perturbation;

d. determining a check value by using the at least one electrochemical cell response;

e. comparing the check value to a limit value to determine a variance;

f. changing the constant polarization voltage by one increment and repeating steps a. through e. with the changed polarization voltage, if the variance is positive; and

g. confirming the polarization voltage as an optimal polarization voltage if the variance is zero or negative.

2. The method of claim 1, wherein the sensor is operated with voltage control and temperature compensation during the function check.

3. The method of claim 2, wherein the check value determining step uses a check function which is system-specific and establishes a mathematical relationship between the electrochemical cell response in the presence of the perturbation and the electrochemical cell response without the perturbation.

4. The method of claim 3, wherein the check function is determined empirically prior to applying the perturbation quantity and is stored in a processing unit.

5. The method of claim 4, wherein the perturbation quantity is a voltage pulse selected from the group consisting of:

rectangular, triangular, sinusoidal and Gaussian.

6. The method of claim 5, wherein the voltage pulse is effective in the system for a duration of 1 to 60 seconds with a maximum value of 100 mV.

7. The method of claim 6, wherein the voltage increment is between 5 and 1000 mV.

8. The method of claim 7, wherein the voltage increment is between 10 and 150 mV.

9. The method of claim 7, wherein the method is performed automatically.

10. The method of claim 1, wherein the check value determining step uses a check function which is system-specific and establishes a mathematical relationship between the electrochemical cell response in the presence of the perturbation and the electrochemical cell response without the perturbation.

11. The method of claim 10, wherein the check function is determined empirically prior to applying the perturbation quantity and is stored in a processing unit.

12. The method of claim 1, wherein the perturbation quantity is a voltage pulse selected from the group consisting of:

rectangular, triangular, sinusoidal and Gaussian.

13. The method of claim 12, wherein the voltage pulse is effective in the system for a duration of 1 to 60 seconds with a maximum value of 100 mV.

14. The method of claim 1, wherein the voltage increment is between 5 and 1000 mV.

15. The method of claim 14, wherein the voltage increment is between 10 and 150 mV.

16. The method of claim 1, wherein the method is performed automatically.

17. A measuring system for performing the method of claim 1, comprising:

an amperometric electrochemical sensor which has an electrochemical cell with at least one working electrode and a counter-electrode, a variably settable voltage source, a current-measuring device, and a computer-supported control- and processing unit in which the method according to claim 1 is implemented.

18. The measuring system of claim 17, wherein the computer-supported processing unit comprises a data memory in which the values for the predetermined increments, the limit values, the perturbation pulses and the initial polarization voltage as well as the check function are stored for different substance concentrations and different sensors.

19. An automated method of checking the function of an amperometric electrochemical sensor which comprises an electrochemical cell, comprising the steps of:

a. providing a computer-supported control- and processing-unit comprising a data memory and a data-evaluating program;

b. using a signal from the control- and processing-unit to apply a constant polarization voltage to the electrochemical cell, the first application of the constant polarization voltage being a constant initial polarization voltage based upon information stored in the data memory;

c. using a signal from the control- and processing-unit to apply a perturbation quantity to the electrochemical cell, the perturbation quantity based upon information stored in the data memory;

d. using a signal received by the control- and processing-unit from the electrochemical cell to determine at least one response of the electrochemical cell in the presence of the perturbation;

e. using the at least one electrochemical cell response to determine a check value, based upon data stored in the data memory;

f. comparing the check value to a limit value stored in the data memory to determine a variance;

g. using a signal from the control- and processing-unit to change the constant polarization voltage by an increment of a size determined by information stored in the data memory and repeating steps b. through f. with the changed polarization voltage, if the variance is positive; and

h. using a signal from the control- and processing-unit to report that the polarization voltage is an optimal polarization voltage, if the variance is zero or negative.