SAMPLE CONCENTRATION DETECTOR WITH TEMPERATURE COMPENSATION

• US 20100007889A1
• Filed: 12/10/2007
• Published: 01/14/2010
• Est. Priority Date: 12/12/2006
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Van Kesteren, Hans W.
• Granted Patent: US 8,233,150 B2
• Time in Patent Office: Days
• US Class Current: 356/436
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 2201/1211 for temperature

Abstract

A sample sensor (200) for detecting a concentration of a sample in a sample mixture, the sample sensor (200) comprising a light source (101), a detector element, a processing section (106) and parameter measuring means. The light source (101) produces a light beam (113) for exciting molecules of the sample. The detector element detects an 5 amount of excited molecules of the sample and provides a detector current indicating the amount. The processing section (106) is coupled to the detector element (103) for processing the detector current to generate an output signal (109) representing the concentration. The processing section (106) comprises a temperature compensation module (112) being arranged for compensating for a temperature dependent wavelength shift of the light source (101) 10 based on at least one measured value of a temperature dependent parameter of the light source (101), other than an output wavelength. The parameter measuring means obtain the at least one measured value.

Claims

1. A sample sensor (200) for detecting a concentration of a sample in a sample mixture, the sample sensor (200) comprising:

a light source (101) for producing a light beam (113) for exciting molecules of the sample,

a detector element for detecting an amount of excited molecules of the sample and providing a detector current indicating the amount,

a processing section (106), coupled to the detector element (103) for processing the detector current to generate an output signal (109) representing the concentration, the processing section (106) comprising a temperature compensation module (112) being arranged for compensating for a temperature dependent wavelength shift of the light source (101) based on at least one measured value of a temperature dependent parameter of the light source (101), other than an output wavelength, and

parameter measuring means for obtaining the at least one measured value.

2. A sample sensor (200) according to claim 1, further comprising a light modulator (102) for modulating the light beam (113) for varying the amount of excited molecules and thereby generating pressure variations in the sample mixture, and wherein the detector element comprises a pressure sensor (103) for converting the pressure variations into the detector current.

3. A sample sensor (200) according to claim 1, wherein the detector element comprises a photodiode (108) for measuring optical absorption caused by the exciting of the molecules of the sample, and for converting the optical absorption into the detector current.

4. A sample sensor (200) according to claim 1, further comprising wavelength adjustment means coupled to the temperature compensation module (112), for performing the compensating by controlling the output wavelength.

5. A sample sensor (200) according to claim 1, wherein the temperature compensation means are arranged for performing the compensating by correcting the output signal (109) for the temperature dependent wavelength shift.

6. A sample sensor (200) according to claim 1, wherein the at least one measured value is an optical output power of the light source (101) and wherein the parameter measuring means comprise an internal photodiode (110) for direct measurement of the optical output power.

7. A sample sensor (200) according to claim 4, wherein the light source is a semiconductor laser diode and the at least one measured value is a threshold forward current through the semiconductor laser diode, beneath which threshold current the optical output power is substantially zero and above which threshold current the optical output power substantially increases.

8. A sample sensor (200) according to claim 1, wherein the light source is a semiconductor laser diode and the at least one measured value is a forward voltage of the semiconductor laser diode.

9. A sample sensor (200) according to claim 4, wherein the temperature compensation module (112) uses a calibration factor from a calibration measurement wherein the optical output power and the detector current have been measured at various temperatures, using a known calibration concentration of the sample and a known calibration driving current for the light source (101).

10. A sample sensor (200) according to claim 7, wherein the temperature compensation module (112) uses the following formula:

$\left[S\right]={\left[S\right]}_{\mathrm{ref}}*\frac{\mathrm{PA}}{{\mathrm{PA}}_{\mathrm{ref}}}*C<br><br>\left(P\right),$

wherein [S] is the concentration of the sample, [S]_ref is the known calibration concentration, PA is the detector current, PA_ref is a detector current during the calibration measurement and C(P) is a calibration factor corresponding to the optical output power, P, during the sample measurement,

PA_ref being derived from the calibration measurement.

11. A sample sensor (200) according to claim 5, wherein the temperature compensation module (112) uses a calibration factor from a calibration measurement wherein the forward voltage and the detector current have been measured at various temperatures, using a known calibration concentration of the sample and a known calibration driving current for the light source (101).

12. A sample sensor (200) according to claim 9, wherein the temperature compensation module (112) uses the following formula:

$\left[S\right]={\left[S\right]}_{\mathrm{ref}}*\frac{\mathrm{PA}}{{\mathrm{PA}}_{\mathrm{ref}}}*C<br><br>\left(V_f\right),$

wherein [S] is the concentration of the sample, [S]_ref is the known calibration concentration, PA is the detector current, PA_ref(V_f) is a detector current during the calibration measurement corresponding to the forward voltage, V_f, and C(V_f) is a calibration factor corresponding to the forward voltage, V_f,

PA_ref(V_f) and C(V_f) being derived from the calibration measurement.

13. A method for determining the calibration factor for temperature compensation of the output signal (109) in a sample sensor (200) according to claim 5, the method comprising:

measuring the optical output power and the detector current at various temperatures while using a known calibration concentration of the sample and a known calibration driving current for the light source (101), and

from the measured optical output powers and the measured detector currents, determining the calibration factor.

14. A method for determining the calibration factor for temperature compensation of the output signal (109) in a sample sensor (200) according to claim 7, the method comprising:

measuring the forward voltage and the detector current at various temperatures while using a known calibration concentration of the sample and a known calibration driving current for the light source (101), and

from the measured forward voltages and the measured detector currents, determining the calibration factor.

15. A method for correcting the output signal (109) of a sample sensor (200) according to claim 1 for a temperature dependent wavelength shift of the light source (101), the method comprising:

measuring at least one value of another temperature dependent parameter of the light source (101), and

correcting the output signal (109) based on the measured at least one value.

16. A method according to claim 13, wherein the at least one value is an optical output power of the light beam (113).

17. A method according to claim 14, wherein the light source is a semiconductor laser diode and the at least one measured value is a threshold forward current through the semiconductor laser diode, beneath which threshold current the optical output power is substantially zero and above which threshold current the optical output power substantially increases.

18. A method according to claim 13, wherein the at least one value is a forward voltage of the light beam (113).

19. A method according to claim 13, wherein the correcting comprises using the calibration factor obtained by performing the method of claim 11.