Method for determining a turbidity and turbidity sensor for implementing the method

Patent metadata

Field	Value
Publication number	US-9671339-B2
Application number	US-201514958012-A
Country	US
Kind code	B2
Filing date	Dec 3, 2015
Priority date	Dec 9, 2014
Publication date	Jun 6, 2017
Grant date	Jun 6, 2017

Abstract

A method for determining a turbidity of a medium in a container using at least one turbidity sensor. Depending on the ambient conditions at the installation location of the turbidity sensor, comprising the following steps: passing transmitted radiation through the medium, wherein the transmitted radiation is converted by interaction with the medium, as a function of the turbidity in the received radiation; receiving the received radiation; converting the received radiation into a scattered light intensity, and determining the turbidity from the scattered light intensity. The method is characterized by the following steps: detecting the chronological sequence of the scattered light intensity; determining a mean value on the basis of the chronological sequence of the scattered light intensity; determining the turbidity from the mean value using a calibration model by assigning a turbidity to each mean value; determining a corrected mean value on the basis of the chronological sequence of the scattered light intensity, by determining a noise parameter from the scattered light intensity, and by determining the corrected mean value from the noise parameter using a noise model, and determining a corrected turbidity at least from the corrected mean value using the calibration model by assigning a corrected turbidity to each corrected mean value. The invention further relates to a turbidity sensor for implementing the method.

First claim

The invention claimed is:

1. A method for determining the turbidity of a medium using at least one turbidity sensor for use in process automation, the method comprising:
calculating parameters for a noise model for the turbidity sensor;
passing transmitted radiation into a medium, wherein the transmitted radiation is converted into received radiation by scattering as a function of turbidity in the medium;
converting the received radiation into a scattered light intensity;
measuring a chronological sequence of the scattered light intensity;
calculating a mean value of the chronological sequence of the scattered light intensity;
calculating a turbidity value from the mean value using a calibration model;
calculating a noise parameter based on the chronological sequence of the scattered light intensity;
calculating a corrected mean value of the chronological sequence of the scattered light intensity using the noise parameter and the noise model;
calculating a corrected turbidity value using at least the corrected mean value and the calibration model;
calculating a turbidity offset by comparing the turbidity value and the corrected turbidity value; and
determining whether the turbidity offset exceeds a threshold, wherein upon determining that the turbidity offset exceeds the threshold, generating a message indicating that the turbidity value contains interference due to an interference variable or an interference source.

2. The method according to claim 1 , wherein:
the corrected turbidity value is calculated using at least the corrected mean value, the mean value, and the calibration model.

3. The method according to claim 1 , further comprising:
upon determining that the turbidity offset exceeds the threshold, compensating the turbidity by determining an actual turbidity using the corrected turbidity.

4. The method according to claim 1 , wherein the noise parameter is calculated using a Fourier transformation of the chronological sequence of the scattered light intensity.

5. The method according to claim 1 , wherein:
the corrected mean value is determined from the noise parameter using the noise model, the noise model defined as,
RK =α*√{square root over ( MW kor )}+β

where RK is the noise parameter, α is a scaling factor for the conversion of an electrical variable to the turbidity, MW kor is the corrected mean value, and β is a constant for the turbidity sensor.

6. The method according to claim 1 , wherein:
said noise parameter depends on ambient conditions and/or the state of the turbidity sensor.

7. The method according to claim 6 , wherein:
the ambient conditions are at least materials, diameter, surface roughness, surface color, surface texture and/or deposits on the container, and/or distance of turbidity sensor to the container.

8. The method according to claim 6 , wherein:
the state of the turbidity sensor is surface texture, deposits, wear of an optical window, and/or contamination at the turbidity sensor.

9. The method according to claim 6 , further comprising the step of:
displaying said noise parameter and/or a message about the ambient condition and/or state of the turbidity sensor.

10. A turbidity device comprising a turbidity sensor and a controller, the turbidity sensor configured to transmit radiation into a medium and to receive radiation scattered by turbidity in the medium, the controller configured to:
convert the received radiation into a scattered light intensity;
measure a chronological sequence of the scattered light intensity;
calculate a mean value of the chronological sequence of the scattered light intensity;
calculate a turbidity value from the mean value using a calibration model;
calculate a noise parameter based on the chronological sequence of the scattered light intensity;
calculate a corrected mean value of the chronological sequence of the scattered light intensity using the noise parameter and a noise model;
calculate a corrected turbidity value using at least the corrected mean value and the calibration model;
calculate a turbidity offset by comparing the turbidity value and the corrected turbidity value; and
determine whether the turbidity offset exceeds a threshold, wherein upon determining that the turbidity offset exceeds the threshold, generate a message indicating that the turbidity value contains interference through an interference variable or an interference source.

11. The turbidity device according to claim 10 , wherein:
the turbidity device comprises a higher-level unit, which determines said noise parameter, the mean value, the corrected mean value, the turbidity and/or the corrected turbidity and performs a comparison of the turbidity with the corrected turbidity, wherein the higher-level unit is part of the turbidity device or is installed in an external device, in particular a transmitter.

12. The turbidity device according to claim 11 , wherein:
the turbidity device is connected with the external device, in particular the transmitter, over an electrically insulated, and in particular,
inductive interface, or the turbidity sensor is connected with the external device, in particular the transmitter, over a wireless, in particular a Bluetooth interface.

13. The method according to claim 1 , wherein the noise parameter is calculated using a standard deviation analysis of the chronological sequence of the scattered light intensity.

14. The method according to claim 1 , wherein the calibration model outputs the turbidity value based on the mean value.

Assignees

• Endress + Hauser Conducta Ges Für Mess—Und Regeltechnik Mbh + Co Kg
• Endress & Hauser Conducta Gmbh & Co Kg

Inventors

• Haase Bjorn
• Grossmann Matthias
• Gotz Carsten
• Kratschmer Thilo

Classifications

• G01N2021/473

  Compensating for unwanted scatter, e.g. reliefs, marks · CPC title

• G01N2021/4711

  Multiangle measurement · CPC title

• G01N15/06 Primary

  Investigating concentration of particle suspensions (by weighing G01N5/00; investigating sedimentation of particle suspensions G01N15/04; investigating individual particles G01N15/10) · CPC title

• G01N2021/4726

  Detecting scatter at 90° · CPC title

• G01N21/51 Primary

  inside a container, e.g. in an ampoule (G01N21/53 takes precedence) · CPC title