Measuring and sensor assembly for determining a characteristic of a fluid and method for operating the same

• US 20050222783A1
• Filed: 12/19/2002
• Published: 10/06/2005
• Est. Priority Date: 01/17/2002
• Status: Active Grant

• Current Assignee: Testo GmbH & Company
• Original Assignee: Testo GmbH & Company
• Inventors: Hall, Jurgen, Muhl, Mike
• Granted Patent: US 7,523,006 B2
• Time in Patent Office: Days
• US Class Current: 702/52
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 33/03 Edible oils or edible fats

Abstract

The aim of the invention is to provide a simple and reliable method of measuring the quality of a fluid (2), in particular an oil or fat. This is achieved by a dielectric measurement in conjunction with a temperature measurement, which are carried out in situ by means of a measuring assembly and a sensor assembly (1) used with the latter, whereby the sensor assembly is submerged in the fluid. This permits information concerning the condition of the fluid, in particular concerning the age of the frying oil or fat, to be obtained in a rapid, low-cost manner.

Claims

1. A measuring system for determining a property of a fluid from a dielectric property of the fluid, comprising:

a first sensor for measuring an electric capacitance and a second sensor for measuring a temperature, wherein the first sensor is designed as a dielectric sensor which may be immersed in the fluid and has a stray-field capacitor which functions as the measuring capacitor, and the second sensor is designed as a temperature sensor which may be immersed in the fluid.

2. The measuring system as recited in claim 1, wherein the first and second sensors are each connected to an analyzer device which assigns a value of the property to be determined to a measured temperature value and a measured electric capacitance value.

3. The measuring system as recited in claim 2, wherein the value of the electric capacitance measured by the dielectric sensor is compared in a comparator device of the analyzer device with a stored reference value assigned to the measured temperature value, and a signal is output as a function of whether the reference value is reached or exceeded.

4. The measuring system as recited in claim 1, further comprising a compensation device for correcting the measured value of the electric capacitance, taking into account a capacitance reference value measured on an auxiliary capacitor situated in proximity to the measuring capacitor.

14. The measuring system as recited in claim 1, wherein the first and second sensors are each connected to an analyzer device which assigns a value of the property to be determined to a measured temperature value and a measured electric capacitance value, and wherein the value of the electric capacitance measured by the dielectric sensor is compared in a comparator device of the analyzer device with a stored reference value assigned to the measured temperature value, and a signal is output as a function of whether the reference value is reached or exceeded.

5. A sensor system for measuring a dielectric property of a fluid, comprising:

a dielectric sensor which may be immersed in the fluid and has a measuring capacitor designed as a stray-field capacitor, wherein the sensor has an auxiliary capacitor and on introduction of the sensor into the fluid, the auxiliary capacitor is not immersed in the fluid until the measuring capacitor is fully immersed in the fluid.

6. The sensor system as recited in claim 5, wherein feeder lines of the measuring capacitor and the auxiliary capacitor are identical in design and are arranged in mutual symmetry.

7. The sensor system as recited in claim 5, wherein the auxiliary capacitor is composed of at least one spur line which ends upstream from the measuring capacitor and is designed and arranged like the feeder lines of the measuring capacitor.

8. The sensor system as recited in claim 5, wherein the measuring capacitor is formed by a plurality of flat printed conductors in the form of interdigital capacitor.

9. The sensor system as recited in claim 8, wherein the printed conductors are printed on an insulating substrate by thin-film or thick-film methods.

10. The sensor system as recited in claim 5, further comprising a temperature sensor in the form of an NTC resistor, a PTC resistor or a temperature element.

11. The sensor system as recited in claim 10, wherein the temperature sensor is connected to the dielectric sensor to form a structural unit.

12. The sensor system as recited in claim 9, wherein feeder lines leading to the temperature sensor are applied to the insulating substrate in the form of printed conductors.

13. The sensor system as recited in claim 11, wherein feeder lines leading to the temperature sensor are applied to the insulating substrate in the form of printed conductors.

15. The sensor system as recited in claim 5, wherein feeder lines of the measuring capacitor and the auxiliary capacitor are identical in design and are arranged in mutual symmetry, wherein the auxiliary capacitor is composed of at least one spur line which ends upstream from the measuring capacitor and is designed and arranged like the feeder lines of the measuring capacitor, wherein the measuring capacitor is formed by a plurality of flat printed conductors in particular in the form of interdigital capacitor, and wherein the printed conductors are printed on an insulating substrate by thin-film or thick-film methods.

16. A measuring device, comprising:

a first sensor that measures a first property of a fluid and outputs a first measured value;

a second sensor that measures a second property of said fluid and outputs a second measured value;

an analyzer device connected to said first and second sensors, wherein said analyzer device compares said first and second measured values with stored reference values and outputs at least one signal based on differentials between said measured values and said stored reference values.

17. The device of claim 16, wherein said first sensor includes a dielectric sensor and said first property is a capacitance of the fluid, and said second sensor includes a temperature sensor and said second property is a temperature of the fluid.

18. The device of claim 16, wherein said first sensor is a capacitor having conductive feeder lines disposed on an insulating substrate.

19. The device of claim 16, further comprising a compensation device that takes calibrating measurements of said first and second properties.

20. The device of claim 19, wherein said compensation device is an auxiliary capacitor disposed in proximity to said first sensor.

21. The device of claim 20, wherein said auxiliary capacitor includes at least one spur line ending upstream from feeder lines of a measuring capacitor of said first sensor and that is symmetrical with the feeder lines of said measuring capacitor.

22. The device of claim 20, where said first sensor is structurally attached to said second sensor.

23. A method for determining a property of a fluid, comprising:

measuring a first property of the fluid;

measuring a second property of the fluid;

comparing measured values of said first and second properties with stored reference values of said first and second properties;

outputting a determination signal based on differentials between said measured values and said stored reference values.

24. The method of claim 23, wherein said first property is a capacitance of the fluid and said second property is a temperature of said fluid.

25. The method of claim 23, further comprising compensating for errors introduced into said measured values.

26. the method of claim 25, wherein said compensating for errors includes immersing said first sensor into said fluid and subsequently immersing a compensation device into said fluid.