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DE-102024210755-A1 - Method for determining a property of a gas using a Raman spectroscopy device

DE102024210755A1DE 102024210755 A1DE102024210755 A1DE 102024210755A1DE-102024210755-A1

Abstract

The invention relates to a method for determining at least one property of a gas, in particular for determining at least one gas concentration, using a Raman spectroscopy device (30), wherein the Raman spectroscopy device (30) comprises a laser diode (16) which is configured for focused illumination of the gas (22), wherein the Raman spectroscopy device (30) has a detector (70) for spectrally resolved detection of the Raman scattered light (34), wherein the at least one property of the gas (22) is determined by means of an evaluation algorithm based on the Raman scattered light (34) detected by the detector (70), wherein a temperature of the laser diode (16) is selectively controlled to one of at least two setpoints, characterized in that the evaluation algorithm is selected based on the respective selected setpoint.

Inventors

  • Sebastian Russ
  • Johannes Weber
  • Alexander Stratmann
  • Theodoros Garavelis
  • Michael Urhahn
  • Jens Schneider

Assignees

  • Robert Bosch Gesellschaft mit beschränkter Haftung

Dates

Publication Date
20260513
Application Date
20241108

Claims (17)

  1. Method for determining at least one property of a gas (22), in particular for determining at least one gas concentration, using a Raman spectroscopy device (30), wherein the Raman spectroscopy device (30) comprises a laser diode (16) designed for focused illumination of the gas (22), wherein the Raman spectroscopy device (30) has a detector (70) for spectrally resolved detection of the Raman scattered light (34), wherein the at least one property of the gas (22) is determined by means of an evaluation algorithm based on the Raman scattered light (34) detected by the detector (70), wherein a temperature of the laser diode (16) is selectively controlled to one of at least two setpoints, characterized in that the evaluation algorithm is selected based on the respective selected setpoint.
  2. Procedure according to Claim 1 , characterized in that the Raman spectroscopy device (30) has a temperature sensor (50) for measuring the ambient temperature, and that the at least two setpoints are selected depending on the ambient temperature, wherein a higher setpoint is always selected at a higher ambient temperature than at a lower ambient temperature.
  3. Procedure according to Claim 1 or 2 , characterized in that the Raman spectroscopy device (30) has a housing (100) with an inner side (100i) and an outer side (100a), wherein the following is arranged in the housing (100): a gas measurement chamber (20) for the gas (22) and one or more optical inlets (28) to the gas measurement chamber (20) and one or more optical outlets (29) from the gas measurement chamber (20) and a collecting optical system (26) with at least one filter and at least one aperture for supplying Raman scattered light (34) from the gas measurement chamber (20) to a spectral analysis unit (38), which is also arranged in the housing (100) and which comprises the detector (70).
  4. Procedure according to Claim 3 , characterized in that a gas supply line for supplying the gas (22) into the gas measurement room (20) is further arranged in the housing (100).
  5. Procedure according to one of the Claims 3 or 4 , characterized in that the temperature sensor (50) is arranged on the laser diode (16) or on the detector (70).
  6. Procedure according to Claim 3 or 4 , characterized in that the temperature sensor (50) is arranged on the inside (100i) of the housing (100) or on the outside (100a) of the housing (100) or outside the housing (100).
  7. Procedure according to one of the Claims 3 until 6 , characterized in that the Raman spectroscopy device (30) has at least one fan for ventilating the interior of the housing (100) and that the temperature sensor (50) for measuring the ambient temperature is blown on by the at least one fan.
  8. Method according to one of the preceding claims, characterized in that the difference between the first setpoint of the operating temperature of the laser diode (16) and the second setpoint of the operating temperature of the laser diode (16) is at least 5 Kelvin and in particular at most 25 Kelvin.
  9. Method according to one of the preceding claims, characterized in that the evaluation algorithm for determining the property of a gas (22) comprises a neural network.
  10. Method according to one of the preceding claims, characterized in that the evaluation algorithm for determining the property of a gas (22) takes into account the dependence of the wavelength of the light emitted by the laser diode (16) and/or the intensity of the light emitted by the laser diode (16) and/or the bandwidth of the light emitted by the laser diode (16) on the operating temperature of the laser diode (16).
  11. Method according to one of the preceding claims, characterized in that the Raman spectroscopy device (30) has a control and regulation device (72), wherein a first control loop (73) and a second control loop (74) are implemented in the Raman spectroscopy device (30), wherein the first control loop (73) is configured to control the temperature of the laser diode (16) to the respective selected setpoint, and that the second control loop (74) is configured to control the temperature of the detector (70) to a setpoint of the detector temperature.
  12. Procedure according to Claim 11 , wherein the setpoint of the detector temperature is always lower than the respective setpoint of the temperature of the laser diode (16).
  13. Method according to one of the preceding claims, characterized in that the laser diode (16) and the detector (70) are thermally are connected by means of at least one passive thermal conductivity structure (76).
  14. Procedure according to Claim 13 , characterized in that the passive heat conduction structure (76) is formed from one or more rod conductors or from one or more heat conduction tubes.
  15. Procedure according to Claim 14 characterized in that the rod(s) or heat conducting tube(s) is/are made of a material with high thermal conductivity, for example aluminum, copper, gold or silver; diamond, boron nitride, silicon carbide, graphite or aluminum oxide.
  16. Procedure according to Claim 13 , 14 or 15 , characterized in that the rod(s) or heat-conducting tube(s) have one or all of the following features: Number: 1 to 100; Length: 1 mm to 200 mm; Total cross-sectional area: 0.1 mm² to 1000 mm² .
  17. Raman spectroscopy apparatus (30) which is configured to perform the method according to one of the preceding claims.

Description

Technical field The invention relates to a method for determining at least one property of a gas, for example a gas concentration, using a Raman spectroscopy device. The Raman spectroscopy device comprises a laser diode configured for focused illumination of the gas and a detector for spectrally resolved detection of the Raman scattered light. State of the art From the US 2023/0010890 A1 A system is known. It comprises a laser for illuminating a sample to be examined, a temperature sensor for detecting the operating temperature of the laser and for generating an output signal indicating the detected temperature, a temperature stabilization device for controlling the operating temperature of the laser, and a controller for determining a target operating temperature or temperature range for the laser based on the output of the temperature sensor and for controlling the temperature stabilization device to bring the operating temperature of the laser to the target operating temperature or target temperature range. Description of the invention The inventors initially recognized that stabilizing the temperature of the laser diode is a necessary prerequisite for maintaining constant emission properties such as wavelength, intensity, and bandwidth. This allows for precise determination of the gas's properties based on the Raman scattered light resulting from the Raman spectroscopy apparatus, using a suitable detector and algorithm. According to the invention, such stabilization is achieved by controlling the laser diode temperature to a setpoint (closed-loop control). In such control loops, the laser diode temperature can be precisely and continuously stabilized at a setpoint. The inventors further recognized that choosing the target temperature for the laser diode is not trivial. While a relatively low temperature generally has a beneficial effect on the emission characteristics and lifetime of the laser diode, the choice of the target temperature, together with the given characteristics of the Raman spectroscopy system, also limits the operating temperature range in which the Raman spectroscopy system can perform meaningful measurements. If the ambient temperature is above this operating temperature range, the Raman spectroscopy system can no longer reliably lower the laser diode temperature to the aforementioned relatively low temperature. To overcome this conflict of objectives, the invention provides that the temperature of the laser diode can be selectively controlled to one of at least two setpoints. Depending on the operating location and the actual or expected ambient temperature, the more suitable of the two setpoints can then be selected. Of course, more than two setpoints can also be provided. It was further recognized that when the temperature of the laser diode changes, the properties of the Raman scattered light also change along with the emission properties of the laser diode. Therefore, it is also part of the present invention that an evaluation algorithm, with which the property of the gas is determined based on the Raman scattered light detected by the detector, is selected according to the respective setpoint. The term "evaluation algorithm" should be interpreted broadly. It could be, for example, a formula or a table. It could also be a trained neural network or something similar. The term "selecting" an evaluation algorithm should also be interpreted broadly. For example, a separate formula or table could be stored for each target temperature, or a separate neural network could be trained and maintained with the data relating to the respective target temperature. However, the selection could also be made, for instance, by individually choosing the parameters of a formula for each target temperature. In a further training course, it is planned that the setpoint temperature of the laser diode will be selected based on the ambient temperature of the Raman spectroscopy system. A higher setpoint can always be selected at higher ambient temperatures than at lower ambient temperatures. The ambient temperature value can be measured by a temperature sensor of the Raman spectroscopy system. Alternatively, the ambient temperature information can also come from another source; for example, corresponding data can be received via a connectivity link of the Raman spectroscopy system. The Raman spectroscopy device may be provided with a housing comprising an inner and an outer surface. This housing may be enclosed, thus protecting the interior, and in particular the Raman spectroscopy device itself, from contamination. All components of the Raman spectroscopy device may be located within this housing. The housing may, in particular, contain: a gas measurement chamber for the gas in which the laser diode emission can be focused; one or more optical access points to the gas measurement chamber, for example, for coupling in the focused emission from the laser diode; one or more optical output points from the gas