CA2824940A1 - An emission spectrometer and method of operation - Google Patents
An emission spectrometer and method of operation Download PDFInfo
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- CA2824940A1 CA2824940A1 CA2824940A CA2824940A CA2824940A1 CA 2824940 A1 CA2824940 A1 CA 2824940A1 CA 2824940 A CA2824940 A CA 2824940A CA 2824940 A CA2824940 A CA 2824940A CA 2824940 A1 CA2824940 A1 CA 2824940A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
- G01N21/274—Calibration, base line adjustment, drift correction
- G01N21/276—Calibration, base line adjustment, drift correction with alternation of sample and standard in optical path
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
- G01N21/718—Laser microanalysis, i.e. with formation of sample plasma
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Abstract
A method of calibrating an emission spectrometer (10) having a detector (11) capable of detecting spectral components of incident radiation, and a measurement optical path (28) which directs an energy beam (26) to a sample (20) and radiation emitted by the sample when irradiated by the energy beam to the radiation detector (11). The method comprises directing radiation of known spectral characteristic along an alternate path to the detector (11). The detector (11) to detects spectral characteristics of the radiation and makes a comparison with the known spectral characteristics. Drift data is determined on a basis of any variation between the detected and known spectral characteristics. The drift data is stored and subsequently used to adjust detected spectral characteristics of a sample in the measurement optical path (28) produce a drift calibrated output spectral analysis of the sample.
Description
AN EMISSION SPECTROMETER AND METHOD OF OPERATION
Field of the Invention The present invention relates to an emission spectrometer and a method of operating the spectrometer.
Background of the Invention Emission spectroscopy involves exciting atoms of a substance and examining the wave length of photons emitted by atoms during transition from an excited state to a lower energy state. Each element in the periodic table emits a characteristic set of discrete wave lengths when its atoms return from an excited state to a lower energy state. By detecting and analysing these wave lengths the elemental composition of a sample can be determined. The atoms can be energised by various types of energy sources which characterise the type of emission spectrometer. For example atoms may be excited by irradiation with electromagnetic radiation such as by a laser, x-rays, or electric discharge.
Irrespective of the energy source, the accuracy and reliability of such emission spectrometers is dependent on the accuracy and quality of the detector and optics used to receive the radiation emitted from the sample. The output of a spectrometer may drift with time and in order to provide reliable outputs from the spectrometer the detector and/or optics response should be checked and the spectrometer calibrated if necessary from time to time.
Summary of the Invention In one aspect the invention provides a method of obtaining an emission spectrum of a sample using an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the detector, the method comprising:
operating an onboard calibration system to generate drift data relating to spectrometer drift;
Field of the Invention The present invention relates to an emission spectrometer and a method of operating the spectrometer.
Background of the Invention Emission spectroscopy involves exciting atoms of a substance and examining the wave length of photons emitted by atoms during transition from an excited state to a lower energy state. Each element in the periodic table emits a characteristic set of discrete wave lengths when its atoms return from an excited state to a lower energy state. By detecting and analysing these wave lengths the elemental composition of a sample can be determined. The atoms can be energised by various types of energy sources which characterise the type of emission spectrometer. For example atoms may be excited by irradiation with electromagnetic radiation such as by a laser, x-rays, or electric discharge.
Irrespective of the energy source, the accuracy and reliability of such emission spectrometers is dependent on the accuracy and quality of the detector and optics used to receive the radiation emitted from the sample. The output of a spectrometer may drift with time and in order to provide reliable outputs from the spectrometer the detector and/or optics response should be checked and the spectrometer calibrated if necessary from time to time.
Summary of the Invention In one aspect the invention provides a method of obtaining an emission spectrum of a sample using an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the detector, the method comprising:
operating an onboard calibration system to generate drift data relating to spectrometer drift;
placing a sample in the measurement optical path, radiating the sample in the optical path and using the detector to produce raw spectral characteristics of radiation emitted by the sample; and, producing an emission spectrum of the sample by using the drift data to compensate the raw spectral characteristics of the sample for spectrometer drift.
In one embodiment operating an onboard calibration system comprises directing radiation of known spectral characteristics to the detector.
In a second aspect the invention provides a method of operating an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the detector, the method comprising:
using an onboard drift calibration system to perform a calibration routine comprising: directing radiation of known spectral characteristics along an alternate optical path to the detector; operating the detector to detect spectral characteristics of the radiation; comparing the detected spectral characteristics with the known spectral characteristics; determining drift data on a basis of any variation between the detected and known spectral characteristics; and storing the drift data; and, performing a measurement routine comprising: placing a sample in the optical path, radiating the sample in the optical path and detecting spectral characteristics of radiation emitted by the sample and using the drift data to compensate spectral characteristics of the sample for spectrometer drift.
In a third aspect the invention provides a method of obtaining an emission spectrum of a sample using an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the radiation detector, the method comprising:
directing radiation of known spectral characteristic to the detector;
operating the detector to detect spectral characteristics of the radiation;
comparing the detected spectral characteristics with the known spectral characteristics;
In one embodiment operating an onboard calibration system comprises directing radiation of known spectral characteristics to the detector.
In a second aspect the invention provides a method of operating an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the detector, the method comprising:
using an onboard drift calibration system to perform a calibration routine comprising: directing radiation of known spectral characteristics along an alternate optical path to the detector; operating the detector to detect spectral characteristics of the radiation; comparing the detected spectral characteristics with the known spectral characteristics; determining drift data on a basis of any variation between the detected and known spectral characteristics; and storing the drift data; and, performing a measurement routine comprising: placing a sample in the optical path, radiating the sample in the optical path and detecting spectral characteristics of radiation emitted by the sample and using the drift data to compensate spectral characteristics of the sample for spectrometer drift.
In a third aspect the invention provides a method of obtaining an emission spectrum of a sample using an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the radiation detector, the method comprising:
directing radiation of known spectral characteristic to the detector;
operating the detector to detect spectral characteristics of the radiation;
comparing the detected spectral characteristics with the known spectral characteristics;
determining drift data on a basis of any variation between the detected and known spectral characteristics;
storing the drift data; and producing an emission spectrum of the sample by using the drift data to compensate raw spectral characteristics of the sample in the measurement optical path for spectrometer drift.
In one embodiment directing radiation of known spectral characteristics to the detector comprises:
providing a standard sample of known characteristics;
diverting the energy beam from the measurement optical path to the standard sample; and, directing radiation emitted by the standard sample to the detector.
Diverting the energy beam may comprise moving a first optical system into the measurement optical path the first optical system operable to direct the energy beam to the standard sample and receive and subsequently directing radiation for the standard sample arising from irradiation by the energy beam to the detector.
The method may comprise varying a point of irradiation of the energy beam on the standard sample on subsequent operations of the spectrometer to determine the drift data.
Varying a point of irradiation may comprise varying a position of the standard sample while maintaining a substantially constant trajectory of the energy beam.
Varying the position of the standard sample may comprise mounting the sample on an X-Y translation device and operating the translation device on each operation of the spectrometer in the drift mode to move the standard sample in a plane in one or both of an X and Y direction.
Alternately varying a point of irradiation may comprise maintaining the standard sample in a fixed position and steering the energy beam to irradiate different points on the standard sample.
storing the drift data; and producing an emission spectrum of the sample by using the drift data to compensate raw spectral characteristics of the sample in the measurement optical path for spectrometer drift.
In one embodiment directing radiation of known spectral characteristics to the detector comprises:
providing a standard sample of known characteristics;
diverting the energy beam from the measurement optical path to the standard sample; and, directing radiation emitted by the standard sample to the detector.
Diverting the energy beam may comprise moving a first optical system into the measurement optical path the first optical system operable to direct the energy beam to the standard sample and receive and subsequently directing radiation for the standard sample arising from irradiation by the energy beam to the detector.
The method may comprise varying a point of irradiation of the energy beam on the standard sample on subsequent operations of the spectrometer to determine the drift data.
Varying a point of irradiation may comprise varying a position of the standard sample while maintaining a substantially constant trajectory of the energy beam.
Varying the position of the standard sample may comprise mounting the sample on an X-Y translation device and operating the translation device on each operation of the spectrometer in the drift mode to move the standard sample in a plane in one or both of an X and Y direction.
Alternately varying a point of irradiation may comprise maintaining the standard sample in a fixed position and steering the energy beam to irradiate different points on the standard sample.
Additionally or alternately directing radiation of known spectral characteristics to the detector may comprise providing a radiation source of known spectrum and directing the radiation from the radiation source of known spectrum to the detector.
Directing the radiation from the radiation source of known spectrum to the detector may comprise moving a second optical system which defines an optical path for the radiation source into position where the radiation from the radiation source is in a field of view of the detector.
The method may comprise diverting a fraction of the energy beam from the measurement optical path and using the diverted fraction to monitor an energy level of the energy beam.
The method may comprise generating an energy level alarm when monitored energy level is below a predetermined minimum energy level.
The method may comprise generating a detector alarm when the variation between the detected and known spectral characteristics is greater than a threshold level.
A further aspect of the invention comprises an emission spectrometer operable to provide a spectral analysis of a sample, said spectrometer comprising:
a detector capable of detecting spectral characteristics of incident radiation;
a measurement optical path arranged to direct an energy beam to a sample location and direct radiation emitted from a sample at the sample location when irradiated by the energy beam to the detector; and, a drift calibration system capable of directing radiation of known spectral characteristic to the detector to produce detected calibration spectral characteristics and adjusting output spectral analysis of a sample on a basis of any variation between the known spectral characteristic and detected calibration spectral characteristics.
The drift calibration system may comprise: a standard sample which when radiated by the energy beam emits radiation of known spectral characteristics;
and, a first optical system movable between: a drift calibration position where the first optical system is operable to divert the energy beam to the standard sample and receive and subsequently direct radiation for the standard sample arising from irradiation by the energy beam to the detector; and, a measurement position where the first optical system is outside of the measurement optical path.
The drift calibration system may be operable to vary a point of incidence of the energy beam on the standard sample on subsequent operations of the drift calibration system.
The drift calibration system may comprise an X-Y translation device on which the standard sample is mounted wherein the translation device is capable of moving the standard sample in a plane in one or both of an X and Y on subsequent operations of the drift calibration system.
The drift calibration system may alternately or additionally comprise a radiation source of known spectrum and a second optical system operable for directing the radiation from the radiation source of known spectrum to the detector.
In one embodiment the second optical system defines an optical path for the radiation source and is movable to a position where the radiation from the radiation source is in a field of view of the detector.
The emission spectrometer may comprise a processor capable of generating drift data on a basis of a comparison between one or both of (a) the known spectral characteristics of the standard sample; and, spectral characteristics of radiation emitted from the standard sample as detected by the detector when the standard sample is irradiated by the energy beam; and (b) a known spectrum of the radiation source; and, the spectrum of the radiation source as detected by the detector.
The drift calibration system may be capable of generating an alarm when a difference between the known spectral characteristics of the standard sample and spectral characteristics of radiation emitted from the standard sample as detected by the detector when the standard sample is irradiated by the energy beam is greater than a threshold level.
Directing the radiation from the radiation source of known spectrum to the detector may comprise moving a second optical system which defines an optical path for the radiation source into position where the radiation from the radiation source is in a field of view of the detector.
The method may comprise diverting a fraction of the energy beam from the measurement optical path and using the diverted fraction to monitor an energy level of the energy beam.
The method may comprise generating an energy level alarm when monitored energy level is below a predetermined minimum energy level.
The method may comprise generating a detector alarm when the variation between the detected and known spectral characteristics is greater than a threshold level.
A further aspect of the invention comprises an emission spectrometer operable to provide a spectral analysis of a sample, said spectrometer comprising:
a detector capable of detecting spectral characteristics of incident radiation;
a measurement optical path arranged to direct an energy beam to a sample location and direct radiation emitted from a sample at the sample location when irradiated by the energy beam to the detector; and, a drift calibration system capable of directing radiation of known spectral characteristic to the detector to produce detected calibration spectral characteristics and adjusting output spectral analysis of a sample on a basis of any variation between the known spectral characteristic and detected calibration spectral characteristics.
The drift calibration system may comprise: a standard sample which when radiated by the energy beam emits radiation of known spectral characteristics;
and, a first optical system movable between: a drift calibration position where the first optical system is operable to divert the energy beam to the standard sample and receive and subsequently direct radiation for the standard sample arising from irradiation by the energy beam to the detector; and, a measurement position where the first optical system is outside of the measurement optical path.
The drift calibration system may be operable to vary a point of incidence of the energy beam on the standard sample on subsequent operations of the drift calibration system.
The drift calibration system may comprise an X-Y translation device on which the standard sample is mounted wherein the translation device is capable of moving the standard sample in a plane in one or both of an X and Y on subsequent operations of the drift calibration system.
The drift calibration system may alternately or additionally comprise a radiation source of known spectrum and a second optical system operable for directing the radiation from the radiation source of known spectrum to the detector.
In one embodiment the second optical system defines an optical path for the radiation source and is movable to a position where the radiation from the radiation source is in a field of view of the detector.
The emission spectrometer may comprise a processor capable of generating drift data on a basis of a comparison between one or both of (a) the known spectral characteristics of the standard sample; and, spectral characteristics of radiation emitted from the standard sample as detected by the detector when the standard sample is irradiated by the energy beam; and (b) a known spectrum of the radiation source; and, the spectrum of the radiation source as detected by the detector.
The drift calibration system may be capable of generating an alarm when a difference between the known spectral characteristics of the standard sample and spectral characteristics of radiation emitted from the standard sample as detected by the detector when the standard sample is irradiated by the energy beam is greater than a threshold level.
The drift calibration system may also be capable of generating an alarm when a difference between the known spectrum of the radiation source; and, the spectrum of the radiation source as detected by the detector is greater than a threshold level.
The emission spectrometer may comprise an energy level monitor capable of monitoring an energy level of the energy beam and providing a signal to the drift calibration system indicative of the monitored energy level.
The emission spectrometer may also be capable of generating an alarm when the monitored energy level is below a threshold energy level.
Brief Description of the Drawings An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 is a schematic representation in block diagram form of a laser induced breakdown spectrometer (LIBS) in accordance with, and incorporating, an embodiment of the present invention;
Figure 2 illustrates operation of the LIBS depicted in Figure 1 in a normal measurement mode where the spectrometer is operated to detect spectral characteristics of a sample;
Figure 3 is a representation of the LIBS shown in Figures 1 and 2 operating in one aspect of a calibration mode;
Figure 4 is a schematic representation of a standard sample used in the first aspect of the calibration mode;
Figure 5 is a representation of a sample translation device incorporated in the LIBS shown in Figures 1 ¨ 3;
Figure 6 is a schematic representation of the LIBS shown in Figures 1 ¨ 4 when operating in a second aspect of the calibration mode; and, Figure 7 is a flow chart depicting an embodiment of a method of obtaining an emission spectrum.
Detailed Description of Preferred Embodiments Embodiments of the present invention are described in relation to an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs: energy to a sample; and, radiation emitted by the sample, when irradiated, to the detector.
The following embodiment is described in the context of a laser induced breakdown spectrometer (LIBS) however the embodiments may be applied to other types of emission spectrometers including but not limited to XRF, XRD, N IR, or NQR spectrometers; spark induced breakdown spectrometers; or atomic emission spectrometers.
In a broad sense, embodiments of the present method and system incorporate an onboard calibration system to enable raw emission spectrum of a sample to be compensated for spectrometer drift. This may be accomplished by directing radiation of known spectral characteristics to the detector. Different sources of radiation of known spectral characteristics may be provided to measure different spectral responses of the spectrometer thereby enabling calibration of the spectrometer to account for one or more drift scenarios of the spectrometer.
In this specification the term "drift' denotes a change in a measured value when the same characteristic of the same (or identical different) sample is measured under the same conditions at different points in time. Spectrometer drift may be due to variations in performance of, among other things, the detector, the energy beam (e.g. laser) or any of the optical elements in the path between the energy beam and the detector.
Embodiments of the invention utilise an onboard calibration system to make drift measurements and generate drift data to enable calibration of the spectrometer and compensation of raw emission spectrum to account for spectrometer drift. This allows for reliable on site/in-situ elemental analysis of samples such as ore sample from a body of ore.
One embodiment of the calibration system utilises a standardised sample of known composition which is irradiated by the energy source of the spectrometer. Assuming that the energy source, detector and optics are functioning in an ideal manner the actual detected/measured (hereinafter referred to as "raw") emission spectrum should accord with the known spectral characteristics of the standardised sample. The raw spectral characteristics are compared with the known or expected characteristics. Variations between the known and raw spectra may then be used to generate calibration data to enable calibration of the spectrometer.
The same or an alternate embodiment utilises radiation of known spectrum provided by a radiation source such as a lamp having a known spectrum which is directed to the detector. The spectrometer is operated to measure the spectral characteristic of the radiation. A comparison is then made between the known or expected spectrum of the radiation source with the raw spectrum of the radiation source as detected by the detector and in any variations therein used to generate calibration data for the spectrometer. Variations between known and raw spectral characteristics may be an indication of detector drift and/or drift in other components of the spectrometer.
Figure 1 is a block diagram, a laser induced breakdown spectrometer (LIBS) 10 incorporating an embodiment of present invention. The LIBS 10 is associated with a conveyor system 12 for conveying samples of material through or past an analysis zone of the LIBS 10. The LIBS 10 comprises a laser and optics system (LOS) 14, an analysis and power system (APS) 16, and a junction box 18 which provides an interface between the LOS 14 and the APS 16. The APS
16 comprises the actual detector (i.e. spectrometer) 11 of the LIBS 10 together with a power source 13 and a processor/computer 15.
The LOS 14 is shown in greater detail in Figure 2 with the LIBS 10 in a measurement mode. In this mode the LIBS 10 detects or measures the spectral characteristics of sample material which may for example be an iron ore sample 20. With reference to Figure 1, the sample 20 is conveyed on the conveyor 12 past an analysis zone of the LIBS 10.
Components of the LOS 14 are disposed in an enclosure or box 22. The components of the LOS 14 comprise a laser 24 which emits a laser beam, and a measurement optical path 28 which: directs the laser beam 26 to the sample 20; and, directs radiation 30 emitted from the sample 20 to the detector 11.
The laser beam 26 provides the energy required to produce emission spectrum from sample 20.
The measurement optical path 28 may be considered as comprising two optical paths, a plasma generation path 32 for the laser 26, and a plasma detection path 34 for the emitted radiation 30. In this embodiment the paths 32 and 34 are co-boresighted. Plasma generation path 32 comprises mirrors 36 and 38, focussing lens 40, and an aperture in pierced mirror 42. During the initial construction and alignment of the optics in the LOS 14, an iris 44 is also located within the plasma generation path 32 between mirror 38 and lens 40. However during normal operation of the LIBS 10, the iris 44 is removed.
When the LIBS 10 is in the measurement mode of operation, laser beam 26 emitted from laser 24 is initially reflected through 90 by mirror 36 to mirror 38 at which it is again reflected through 90 . The laser beam 26 subsequently passes through the lens 40 and the aperture in the pierced mirror 42, through a shroud 46 and onto the sample 20. The laser beam striking the sample 20 excites atoms within the sample to higher energy levels which subsequently emit radiation 30 when transitioning back to lower energy states. A portion of the emitted radiation 30 travels through the shroud 46 and is reflected by mirror to a collector 48 which reflects the emitted radiation 30 to an end of a spectrometer fibre 50 held in a terminal block 51. The radiation then travels through the fibre 50 to the spectrometer housed within the APS 16. Mirror 36 is further arranged to allow a fraction 26a of laser beam 26 to be diverted to an energy gauge 52. The path of the emitted radiation 30 from the sample 20 to the mirror 42, collector 48 and to the end of fibre 50 held terminal block 51 constitutes the plasma detection path 34.
A number of the optical elements in the measurement optical path 28, namely lens 40, mirror 42, collected 48, and a terminal block 51 for the optical fibre 50 are mounted on a moveable platform 56 which provides an auto focussing feature of the LIBS 10. The automatic focussing feature is not an essential or critical part of the present invention and is described in greater detail in patent application no US 61/388,722.
Thus, in measurement mode of operation the measurement optical path 28 directs laser beam 26 to the sample 20 and subsequently directs emitted radiation 30 from the sample 20 to the detector.
The detector 11 then operates to provide a spectral analysis of sample 20 and a corresponding raw emission spectrum.
The provision of an energy source such as laser 24 in the present embodiment, and a measurement optical path 28 for directing energy to the sample 20 and subsequently directing emitted radiation from the sample 20 to a detector is replicated in various types of emission spectrometers. However, the ability in the present embodiment of the LIBS 10 to be calibrated to account for detector drift is enabled by providing an onboard compensation system which is operable to direct radiation of known spectral characteristics along an alternate optical path to the detector. The detector 11 is then operated to detect the spectral characteristics of the known radiation and a comparison is made by processor 15 between the detected spectral characteristics and the known spectral characteristics. Drift data is then generated by processor 15 on a basis of variations between the detected and known spectral characteristics.
Spectrometer 10 can be arranged to automatically perform the calibration routine upon every "power up". Additionally or alternately however controls may be provided to run the calibration routine on demand..
In the present embodiment, the spectrometer incorporates a calibration system CS to enable calibration of the spectrometer and compensation of raw spectral measurements made of samples. When the calibration system CS is in operation the spectrometer is said to be in the calibration mode. Conversely when the calibration system CS in not in operation the spectrometer 10 is in the measurement mode.
The calibration system CS uses one or both of two mechanisms or systems to direct radiation of known spectral characteristics to the detector. The first of these mechanisms utilises a test or standardised sample 60 (see Figures 3 ¨ 5) which is disposed in the enclosure 22 and a first optical system 62 that is operable to create an alternate optical path to direct laser beam 26 onto the standardised sample 60 and the radiation emitted from the sample 60 to the detector 11 optical fibre 50. Optical system 62 comprises a prism 64 mounted on a translation slide 66. When operating the LIBS 10 in a calibration mode, the slide 66 moves the prism 64 to the right to intercept the laser beam 26 between mirror 42 and shroud 46 and reflect the laser beam through 90 onto the standardised sample 60. A portion 68 of the emitted radiation by the standardised sample is directed back to prism 40 where it is reflected to mirror 42 and subsequently directed by collector 48 to optical fibre 50. The radiation emitted by the standardised sample 68 has a known (i.e. a "benchmark") spectrum when radiated by laser beam 26. This known spectrum is stored in a memory of or associated with the processor 15. The detector 11 receives the emitted radiation 68 and operates to detect the spectral characteristics of the radiation. This measured spectrum is also delivered to the processor 15 and a comparison is made between the measured and previously stored expected spectral characteristics. Calibration data for example in the form of a normalisation curve may be produced using various mathematical techniques based on a difference between the measured and known or expected spectral characteristics. Some examples of mathematical techniques include lookup tables, principle component regression analysis, cluster regression analysis, search-match methods, Gaussian techniques, whole pattern methods, condition-based peak modelling, etc. It is to be appreciated that a person skilled in the art would be familiar with appropriate mathematical techniques for facilitating the compensation via suitable calibration data. The calibration data is then used when the LIBS 10 is in the measurement mode to calibrate or standardise the output (raw) spectrum of the sample 20 and thereby compensate for drift or other anomalies in the spectrometer.
Once the detector 11 has detected the emitted radiation 68, and the calibration data has been generated the first optical system 62 is retracted moving the prism 64 out of the plasma generation path 32. The LIBS 10 may now be operated in the measurement mode.
The drift calibration mode may be either run on demand, or automatically run on each operation of the LIBS 10. There is a possibility that radiating the same spot repeatedly on the standardised sample may result in varying spectrums being produced. Accordingly on subsequent operations of the drift calibration mode, the point of irradiation of the sample 60 by laser beam 26 is varied in order to ensure consistency in the benchmark spectrum of the sample. That is, on subsequent operations of the calibration mode, different points on the sample 60 are irradiated with laser beam 26. The different points of irradiation on sample 60 is illustrated by the grid 70 appearing in Figure 4 where each white square in the grid represents a different point of irradiation on the sample 60.
In the present embodiment the variation in the point of irradiation is achieved by mounting sample 60 on an X-Y translation device 72 which is mounted within a housing 74. The translation device 72 operates to increment the position of sample 60 relative to the first optical system 62 so that on each operation or run of the calibration mode a different point on the surface of sample 60 is positioned in alignment with the path of laser beam 26.
Figure 6 illustrates the second mechanism of the calibration system CS. This mechanism may be considered as providing a wave length calibration mode and utilises a lamp 78 (for example a mercury argon lamp) which produces radiation of a known wave length and a second optical system 80 which is able to selectively direct the radiation from lamp 78 to the detector 11 via the optical fibre 50. Optical system 80 comprises an optical fibre 82 which is arranged at one end to receive light from the lamp 78 and held at an opposite end in a coupler 84 supported on a slidable table 86. The coupler 84 holds the end of optical fibre 82 so as to move with linear translation of the table 86. The light transmitted by fibre 82 passes through a lens 88, to a mirror 90 which reflects the radiation through 90 to a further lens 92. Lens 92 directs the radiation from lamp 78 to the fibre 50 and thus to the detector 11. The wavelength spectrum produced by detector 11 is provided to processor 15. Processor 15 compares the measured or raw wavelength spectrum with the expected or known wavelength spectrum of lamp 78. Any variations between the measured and expected spectra are used by processor 15 to generate wavelength calibration data which is subsequently used to adjust or standardise the raw output of the LIBS 10 during its measurement mode. When this aspect of the calibration mode is not in operation table 86 is moved to the left withdrawing the optical system 80 from the measurement optical path 28 thereby enabling operation of the LIBS 10 in the measurement mode.
As previously described the calibration mode may be run on demand or alternately on each successive operation or use of the LIBS 10. For example, it is envisaged that every time LIBS 10 is to be used to obtain the emission spectrum of a sample, the calibration mode is automatically run as part of a power up or start-up routine of a LIBS 10. Calibration data can then be generated and used to adjust or standardise the raw output of the LIBS 10 during its normal measurement mode. This provides an autonomous drift calibration regime. It is further envisaged that the LIBS 10 and in particular processor 15, when generating calibration data may be programmed or otherwise arranged to issue an alarm in the event that the variation between known and measured spectral characteristics either from the standard sample 60 or the lamp 78 exceed a predetermined threshold. This may be operated in conjunction with measurements of the output power of the laser 24 made by the energy gauge 52. The processor 15 may be programmed to determine whether or not the laser energy is at a predetermined minimum energy level. In the event that the energy level of the laser beam is detected as dropping below the threshold level, the LIBS 10 may generate a further alarm indicative of this condition. This information is also useful in the event that during calibration a variance between known and measured spectrum lie outside a prescribed range. If such variance is outside the prescribed range and the laser energy level is at or above a required minimum level, then it can be concluded that the variance arises from a detector or optics issue and not as a result of a reduction in laser energy level.
Figure 7 is a flow chart depicting very broadly a method 100 of using or operating the LIBS 10 to obtain an omission spectrum of a sample.
The initial step 102 in the method 100 is to operate an on board calibration system CS to obtain calibration data for the LIBS 10. As described herein above, the calibration data may be obtained by one or both of two separate processes. The first is to utilise the standardised sample 60 by operating the first optical system 62 to divert laser beam 26 from the measurement optical path 28 to the sample 60. The calibration data may then be obtained by comparison between the measured spectrum of a sample 60 against the expected or known measured spectrum for the sample. The second process is to utilise the lamp 78 having a known wave length and directing radiation from the lamp to the detector 11. Again a comparison is made between the measured spectral characteristics of the lamp 78 and the known characteristics.
Differences between these measurements are used as alternate or additional calibration data.
Once the calibration process at step 102 has been completed, the next step 104 in the method 100 is performed where the LIBS 10 is operated to detect spectral characteristics of the sample 20. This produces raw spectral data or a raw submission spectrum for the sample 20.
Finally, at step 106 in the method 100 the raw spectral characteristics of the sample 20 are compensated by use of the compensation data obtained in step 102 to produce an emission spectrum of sample 20 which is compensated for spectrometer drift.
Now that embodiments of the present invention have been described in detail it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, the calibration of the LIBS 10 using the standard sample 60 relies on sequential movement of the sample 60 by an X-Y
translation device 72 in order to vary the part of irradiation of sample 60 by laser beam 26. However in an alternate embodiment an identical effect may be achieved by use of steering optics which direct laser beam 26 to different points on the sample 60 while the sample 60 is maintained stationary. Further, while the emission spectrometer described in this embodiment is a laser induced breakdown spectrometer, as previously mentioned, embodiments of the present invention may be operated and used with different types of emission spectrometers. In addition in the described embodiment the LOS 14 is provided with various optical elements in the measurement optical path 28 being moveable mounted to enable automatic focus. However this is not an aspect of the invention and embodiments of the invention may be worked equally with an emission spectrometer having a fixed focus system.
All such modifications and variations together with others that would be obvious to persons of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description and the appended claims.
The emission spectrometer may comprise an energy level monitor capable of monitoring an energy level of the energy beam and providing a signal to the drift calibration system indicative of the monitored energy level.
The emission spectrometer may also be capable of generating an alarm when the monitored energy level is below a threshold energy level.
Brief Description of the Drawings An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 is a schematic representation in block diagram form of a laser induced breakdown spectrometer (LIBS) in accordance with, and incorporating, an embodiment of the present invention;
Figure 2 illustrates operation of the LIBS depicted in Figure 1 in a normal measurement mode where the spectrometer is operated to detect spectral characteristics of a sample;
Figure 3 is a representation of the LIBS shown in Figures 1 and 2 operating in one aspect of a calibration mode;
Figure 4 is a schematic representation of a standard sample used in the first aspect of the calibration mode;
Figure 5 is a representation of a sample translation device incorporated in the LIBS shown in Figures 1 ¨ 3;
Figure 6 is a schematic representation of the LIBS shown in Figures 1 ¨ 4 when operating in a second aspect of the calibration mode; and, Figure 7 is a flow chart depicting an embodiment of a method of obtaining an emission spectrum.
Detailed Description of Preferred Embodiments Embodiments of the present invention are described in relation to an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs: energy to a sample; and, radiation emitted by the sample, when irradiated, to the detector.
The following embodiment is described in the context of a laser induced breakdown spectrometer (LIBS) however the embodiments may be applied to other types of emission spectrometers including but not limited to XRF, XRD, N IR, or NQR spectrometers; spark induced breakdown spectrometers; or atomic emission spectrometers.
In a broad sense, embodiments of the present method and system incorporate an onboard calibration system to enable raw emission spectrum of a sample to be compensated for spectrometer drift. This may be accomplished by directing radiation of known spectral characteristics to the detector. Different sources of radiation of known spectral characteristics may be provided to measure different spectral responses of the spectrometer thereby enabling calibration of the spectrometer to account for one or more drift scenarios of the spectrometer.
In this specification the term "drift' denotes a change in a measured value when the same characteristic of the same (or identical different) sample is measured under the same conditions at different points in time. Spectrometer drift may be due to variations in performance of, among other things, the detector, the energy beam (e.g. laser) or any of the optical elements in the path between the energy beam and the detector.
Embodiments of the invention utilise an onboard calibration system to make drift measurements and generate drift data to enable calibration of the spectrometer and compensation of raw emission spectrum to account for spectrometer drift. This allows for reliable on site/in-situ elemental analysis of samples such as ore sample from a body of ore.
One embodiment of the calibration system utilises a standardised sample of known composition which is irradiated by the energy source of the spectrometer. Assuming that the energy source, detector and optics are functioning in an ideal manner the actual detected/measured (hereinafter referred to as "raw") emission spectrum should accord with the known spectral characteristics of the standardised sample. The raw spectral characteristics are compared with the known or expected characteristics. Variations between the known and raw spectra may then be used to generate calibration data to enable calibration of the spectrometer.
The same or an alternate embodiment utilises radiation of known spectrum provided by a radiation source such as a lamp having a known spectrum which is directed to the detector. The spectrometer is operated to measure the spectral characteristic of the radiation. A comparison is then made between the known or expected spectrum of the radiation source with the raw spectrum of the radiation source as detected by the detector and in any variations therein used to generate calibration data for the spectrometer. Variations between known and raw spectral characteristics may be an indication of detector drift and/or drift in other components of the spectrometer.
Figure 1 is a block diagram, a laser induced breakdown spectrometer (LIBS) 10 incorporating an embodiment of present invention. The LIBS 10 is associated with a conveyor system 12 for conveying samples of material through or past an analysis zone of the LIBS 10. The LIBS 10 comprises a laser and optics system (LOS) 14, an analysis and power system (APS) 16, and a junction box 18 which provides an interface between the LOS 14 and the APS 16. The APS
16 comprises the actual detector (i.e. spectrometer) 11 of the LIBS 10 together with a power source 13 and a processor/computer 15.
The LOS 14 is shown in greater detail in Figure 2 with the LIBS 10 in a measurement mode. In this mode the LIBS 10 detects or measures the spectral characteristics of sample material which may for example be an iron ore sample 20. With reference to Figure 1, the sample 20 is conveyed on the conveyor 12 past an analysis zone of the LIBS 10.
Components of the LOS 14 are disposed in an enclosure or box 22. The components of the LOS 14 comprise a laser 24 which emits a laser beam, and a measurement optical path 28 which: directs the laser beam 26 to the sample 20; and, directs radiation 30 emitted from the sample 20 to the detector 11.
The laser beam 26 provides the energy required to produce emission spectrum from sample 20.
The measurement optical path 28 may be considered as comprising two optical paths, a plasma generation path 32 for the laser 26, and a plasma detection path 34 for the emitted radiation 30. In this embodiment the paths 32 and 34 are co-boresighted. Plasma generation path 32 comprises mirrors 36 and 38, focussing lens 40, and an aperture in pierced mirror 42. During the initial construction and alignment of the optics in the LOS 14, an iris 44 is also located within the plasma generation path 32 between mirror 38 and lens 40. However during normal operation of the LIBS 10, the iris 44 is removed.
When the LIBS 10 is in the measurement mode of operation, laser beam 26 emitted from laser 24 is initially reflected through 90 by mirror 36 to mirror 38 at which it is again reflected through 90 . The laser beam 26 subsequently passes through the lens 40 and the aperture in the pierced mirror 42, through a shroud 46 and onto the sample 20. The laser beam striking the sample 20 excites atoms within the sample to higher energy levels which subsequently emit radiation 30 when transitioning back to lower energy states. A portion of the emitted radiation 30 travels through the shroud 46 and is reflected by mirror to a collector 48 which reflects the emitted radiation 30 to an end of a spectrometer fibre 50 held in a terminal block 51. The radiation then travels through the fibre 50 to the spectrometer housed within the APS 16. Mirror 36 is further arranged to allow a fraction 26a of laser beam 26 to be diverted to an energy gauge 52. The path of the emitted radiation 30 from the sample 20 to the mirror 42, collector 48 and to the end of fibre 50 held terminal block 51 constitutes the plasma detection path 34.
A number of the optical elements in the measurement optical path 28, namely lens 40, mirror 42, collected 48, and a terminal block 51 for the optical fibre 50 are mounted on a moveable platform 56 which provides an auto focussing feature of the LIBS 10. The automatic focussing feature is not an essential or critical part of the present invention and is described in greater detail in patent application no US 61/388,722.
Thus, in measurement mode of operation the measurement optical path 28 directs laser beam 26 to the sample 20 and subsequently directs emitted radiation 30 from the sample 20 to the detector.
The detector 11 then operates to provide a spectral analysis of sample 20 and a corresponding raw emission spectrum.
The provision of an energy source such as laser 24 in the present embodiment, and a measurement optical path 28 for directing energy to the sample 20 and subsequently directing emitted radiation from the sample 20 to a detector is replicated in various types of emission spectrometers. However, the ability in the present embodiment of the LIBS 10 to be calibrated to account for detector drift is enabled by providing an onboard compensation system which is operable to direct radiation of known spectral characteristics along an alternate optical path to the detector. The detector 11 is then operated to detect the spectral characteristics of the known radiation and a comparison is made by processor 15 between the detected spectral characteristics and the known spectral characteristics. Drift data is then generated by processor 15 on a basis of variations between the detected and known spectral characteristics.
Spectrometer 10 can be arranged to automatically perform the calibration routine upon every "power up". Additionally or alternately however controls may be provided to run the calibration routine on demand..
In the present embodiment, the spectrometer incorporates a calibration system CS to enable calibration of the spectrometer and compensation of raw spectral measurements made of samples. When the calibration system CS is in operation the spectrometer is said to be in the calibration mode. Conversely when the calibration system CS in not in operation the spectrometer 10 is in the measurement mode.
The calibration system CS uses one or both of two mechanisms or systems to direct radiation of known spectral characteristics to the detector. The first of these mechanisms utilises a test or standardised sample 60 (see Figures 3 ¨ 5) which is disposed in the enclosure 22 and a first optical system 62 that is operable to create an alternate optical path to direct laser beam 26 onto the standardised sample 60 and the radiation emitted from the sample 60 to the detector 11 optical fibre 50. Optical system 62 comprises a prism 64 mounted on a translation slide 66. When operating the LIBS 10 in a calibration mode, the slide 66 moves the prism 64 to the right to intercept the laser beam 26 between mirror 42 and shroud 46 and reflect the laser beam through 90 onto the standardised sample 60. A portion 68 of the emitted radiation by the standardised sample is directed back to prism 40 where it is reflected to mirror 42 and subsequently directed by collector 48 to optical fibre 50. The radiation emitted by the standardised sample 68 has a known (i.e. a "benchmark") spectrum when radiated by laser beam 26. This known spectrum is stored in a memory of or associated with the processor 15. The detector 11 receives the emitted radiation 68 and operates to detect the spectral characteristics of the radiation. This measured spectrum is also delivered to the processor 15 and a comparison is made between the measured and previously stored expected spectral characteristics. Calibration data for example in the form of a normalisation curve may be produced using various mathematical techniques based on a difference between the measured and known or expected spectral characteristics. Some examples of mathematical techniques include lookup tables, principle component regression analysis, cluster regression analysis, search-match methods, Gaussian techniques, whole pattern methods, condition-based peak modelling, etc. It is to be appreciated that a person skilled in the art would be familiar with appropriate mathematical techniques for facilitating the compensation via suitable calibration data. The calibration data is then used when the LIBS 10 is in the measurement mode to calibrate or standardise the output (raw) spectrum of the sample 20 and thereby compensate for drift or other anomalies in the spectrometer.
Once the detector 11 has detected the emitted radiation 68, and the calibration data has been generated the first optical system 62 is retracted moving the prism 64 out of the plasma generation path 32. The LIBS 10 may now be operated in the measurement mode.
The drift calibration mode may be either run on demand, or automatically run on each operation of the LIBS 10. There is a possibility that radiating the same spot repeatedly on the standardised sample may result in varying spectrums being produced. Accordingly on subsequent operations of the drift calibration mode, the point of irradiation of the sample 60 by laser beam 26 is varied in order to ensure consistency in the benchmark spectrum of the sample. That is, on subsequent operations of the calibration mode, different points on the sample 60 are irradiated with laser beam 26. The different points of irradiation on sample 60 is illustrated by the grid 70 appearing in Figure 4 where each white square in the grid represents a different point of irradiation on the sample 60.
In the present embodiment the variation in the point of irradiation is achieved by mounting sample 60 on an X-Y translation device 72 which is mounted within a housing 74. The translation device 72 operates to increment the position of sample 60 relative to the first optical system 62 so that on each operation or run of the calibration mode a different point on the surface of sample 60 is positioned in alignment with the path of laser beam 26.
Figure 6 illustrates the second mechanism of the calibration system CS. This mechanism may be considered as providing a wave length calibration mode and utilises a lamp 78 (for example a mercury argon lamp) which produces radiation of a known wave length and a second optical system 80 which is able to selectively direct the radiation from lamp 78 to the detector 11 via the optical fibre 50. Optical system 80 comprises an optical fibre 82 which is arranged at one end to receive light from the lamp 78 and held at an opposite end in a coupler 84 supported on a slidable table 86. The coupler 84 holds the end of optical fibre 82 so as to move with linear translation of the table 86. The light transmitted by fibre 82 passes through a lens 88, to a mirror 90 which reflects the radiation through 90 to a further lens 92. Lens 92 directs the radiation from lamp 78 to the fibre 50 and thus to the detector 11. The wavelength spectrum produced by detector 11 is provided to processor 15. Processor 15 compares the measured or raw wavelength spectrum with the expected or known wavelength spectrum of lamp 78. Any variations between the measured and expected spectra are used by processor 15 to generate wavelength calibration data which is subsequently used to adjust or standardise the raw output of the LIBS 10 during its measurement mode. When this aspect of the calibration mode is not in operation table 86 is moved to the left withdrawing the optical system 80 from the measurement optical path 28 thereby enabling operation of the LIBS 10 in the measurement mode.
As previously described the calibration mode may be run on demand or alternately on each successive operation or use of the LIBS 10. For example, it is envisaged that every time LIBS 10 is to be used to obtain the emission spectrum of a sample, the calibration mode is automatically run as part of a power up or start-up routine of a LIBS 10. Calibration data can then be generated and used to adjust or standardise the raw output of the LIBS 10 during its normal measurement mode. This provides an autonomous drift calibration regime. It is further envisaged that the LIBS 10 and in particular processor 15, when generating calibration data may be programmed or otherwise arranged to issue an alarm in the event that the variation between known and measured spectral characteristics either from the standard sample 60 or the lamp 78 exceed a predetermined threshold. This may be operated in conjunction with measurements of the output power of the laser 24 made by the energy gauge 52. The processor 15 may be programmed to determine whether or not the laser energy is at a predetermined minimum energy level. In the event that the energy level of the laser beam is detected as dropping below the threshold level, the LIBS 10 may generate a further alarm indicative of this condition. This information is also useful in the event that during calibration a variance between known and measured spectrum lie outside a prescribed range. If such variance is outside the prescribed range and the laser energy level is at or above a required minimum level, then it can be concluded that the variance arises from a detector or optics issue and not as a result of a reduction in laser energy level.
Figure 7 is a flow chart depicting very broadly a method 100 of using or operating the LIBS 10 to obtain an omission spectrum of a sample.
The initial step 102 in the method 100 is to operate an on board calibration system CS to obtain calibration data for the LIBS 10. As described herein above, the calibration data may be obtained by one or both of two separate processes. The first is to utilise the standardised sample 60 by operating the first optical system 62 to divert laser beam 26 from the measurement optical path 28 to the sample 60. The calibration data may then be obtained by comparison between the measured spectrum of a sample 60 against the expected or known measured spectrum for the sample. The second process is to utilise the lamp 78 having a known wave length and directing radiation from the lamp to the detector 11. Again a comparison is made between the measured spectral characteristics of the lamp 78 and the known characteristics.
Differences between these measurements are used as alternate or additional calibration data.
Once the calibration process at step 102 has been completed, the next step 104 in the method 100 is performed where the LIBS 10 is operated to detect spectral characteristics of the sample 20. This produces raw spectral data or a raw submission spectrum for the sample 20.
Finally, at step 106 in the method 100 the raw spectral characteristics of the sample 20 are compensated by use of the compensation data obtained in step 102 to produce an emission spectrum of sample 20 which is compensated for spectrometer drift.
Now that embodiments of the present invention have been described in detail it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, the calibration of the LIBS 10 using the standard sample 60 relies on sequential movement of the sample 60 by an X-Y
translation device 72 in order to vary the part of irradiation of sample 60 by laser beam 26. However in an alternate embodiment an identical effect may be achieved by use of steering optics which direct laser beam 26 to different points on the sample 60 while the sample 60 is maintained stationary. Further, while the emission spectrometer described in this embodiment is a laser induced breakdown spectrometer, as previously mentioned, embodiments of the present invention may be operated and used with different types of emission spectrometers. In addition in the described embodiment the LOS 14 is provided with various optical elements in the measurement optical path 28 being moveable mounted to enable automatic focus. However this is not an aspect of the invention and embodiments of the invention may be worked equally with an emission spectrometer having a fixed focus system.
All such modifications and variations together with others that would be obvious to persons of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description and the appended claims.
Claims (27)
1. A method of obtaining an emission spectrum of a sample using an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the detector, the method comprising:
operating an onboard calibration system to generate drift data relating to spectrometer drift;
placing a sample in the measurement optical path, radiating the sample in the optical path and using the detector to produce raw spectral characteristics of radiation emitted by the sample; and, producing an emission spectrum of the sample by using the drift data to compensate the raw spectral characteristics of the sample for spectrometer drift.
operating an onboard calibration system to generate drift data relating to spectrometer drift;
placing a sample in the measurement optical path, radiating the sample in the optical path and using the detector to produce raw spectral characteristics of radiation emitted by the sample; and, producing an emission spectrum of the sample by using the drift data to compensate the raw spectral characteristics of the sample for spectrometer drift.
2. The method according to claim 1 wherein operating an onboard calibration system comprises directing radiation of known spectral characteristics to the detector.
3. A method of operating an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the detector, the method comprising:
using an onboard drift calibration system to perform a calibration routine comprising: directing radiation of known spectral characteristics along an alternate optical path to the detector; operating the detector to detect spectral characteristics of the radiation; comparing the detected spectral characteristics with the known spectral characteristics; determining drift data on a basis of any variation between the detected and known spectral characteristics; and storing the drift data; and, performing a measurement routine comprising: placing a sample in the optical path, radiating the sample in the optical path and detecting spectral characteristics of radiation emitted by the sample and using the drift data to compensate spectral characteristics of the sample for spectrometer drift.
using an onboard drift calibration system to perform a calibration routine comprising: directing radiation of known spectral characteristics along an alternate optical path to the detector; operating the detector to detect spectral characteristics of the radiation; comparing the detected spectral characteristics with the known spectral characteristics; determining drift data on a basis of any variation between the detected and known spectral characteristics; and storing the drift data; and, performing a measurement routine comprising: placing a sample in the optical path, radiating the sample in the optical path and detecting spectral characteristics of radiation emitted by the sample and using the drift data to compensate spectral characteristics of the sample for spectrometer drift.
4. A method of obtaining an emission spectrum of a sample using an emission spectrometer having a detector capable of detecting spectral characteristics of incident radiation, and a measurement optical path which directs an energy beam to a sample and radiation emitted by the sample when irradiated by the energy beam to the radiation detector, the method comprising:
directing radiation of known spectral characteristic to the detector;
operating the detector to detect spectral characteristics of the radiation;
comparing the detected spectral characteristics with the known spectral characteristics;
determining drift data on a basis of any variation between the detected and known spectral characteristics;
storing the drift data; and producing an emission spectrum of the sample by using the drift data to compensate raw spectral characteristics of the sample in the measurement optical path for spectrometer drift.
directing radiation of known spectral characteristic to the detector;
operating the detector to detect spectral characteristics of the radiation;
comparing the detected spectral characteristics with the known spectral characteristics;
determining drift data on a basis of any variation between the detected and known spectral characteristics;
storing the drift data; and producing an emission spectrum of the sample by using the drift data to compensate raw spectral characteristics of the sample in the measurement optical path for spectrometer drift.
5. The method according to any one of claims 2 to 4 wherein directing radiation of known spectral characteristics to the detector comprises:
providing a standard sample of known characteristics;
diverting the energy beam from the measurement optical path to the standard sample; and, directing radiation emitted by the standard sample to the detector.
providing a standard sample of known characteristics;
diverting the energy beam from the measurement optical path to the standard sample; and, directing radiation emitted by the standard sample to the detector.
6. The method according to claim 5 wherein diverting the energy beam comprises moving a first optical system into the measurement optical path the first optical system operable to direct the energy beam to the standard sample and receive and subsequently directing radiation for the standard sample arising from irradiation by the energy beam to the detector.
7. The method according to claim 5 or 6 comprising varying a point of irradiation of the energy beam on the standard sample on subsequent operations of the spectrometer to determine the drift data.
8. The method according to claim 7 wherein varying a point of irradiation comprises varying a position of the standard sample while maintaining a substantially constant trajectory of the energy beam.
9. The method according to claim 8 wherein varying a position of the standard sample comprises mounting the sample on an X-Y translation device and operating the translation device on each operation of the spectrometer in the drift mode to move the standard sample in a plane in one or both of an X
and Y direction.
and Y direction.
10. The method according to claim 7 wherein varying a point of irradiation comprises maintaining the standard sample in a fixed position and steering the energy beam to irradiate different points on the standard sample.
11. The method according to any one of claims 2 to 4 wherein directing radiation of known spectral characteristics to the detector comprises providing a radiation source of known spectrum and directing the radiation from the radiation source of known spectrum to the detector.
12. The method according to any one of claims 2 to 10 further comprising providing a radiation source of known spectrum and directing the radiation from the radiation source of known spectrum to the detector.
13. The method according to claim 11 or 12 wherein directing the radiation from the radiation source of known spectrum to the detector comprises moving a second optical system which defines an optical path for the radiation source into a position where the radiation from the radiation source is in a field of view of the detector.
14. The method according to any one of claims 1 to 13 comprising diverting a fraction of the energy beam from the measurement optical path and using the diverted fraction to monitor an energy level of the energy beam.
15. The method according to claim 14 comprising generating an energy level alarm when monitored energy level is below a predetermined minimum energy level.
16. The method according to claim 4 or any claim dependant on claims 4 comprising generating a detector alarm when the variation between the detected and known spectral characteristics is greater than a threshold level.
17. An emission spectrometer operable to provide a spectral analysis of a sample, said spectrometer comprising:
a detector capable of detecting spectral characteristics of incident radiation ;
a measurement optical path arranged to direct an energy beam to a sample location and direct radiation emitted from a sample at the sample location when irradiated by the energy beam to the detector; and, a drift calibration system capable of directing radiation of known spectral characteristic to the detector to produce detected calibration spectral characteristics and compensating raw spectral characteristics of a sample on a basis of any variation between the known spectral characteristic and detected calibration spectral characteristics.
a detector capable of detecting spectral characteristics of incident radiation ;
a measurement optical path arranged to direct an energy beam to a sample location and direct radiation emitted from a sample at the sample location when irradiated by the energy beam to the detector; and, a drift calibration system capable of directing radiation of known spectral characteristic to the detector to produce detected calibration spectral characteristics and compensating raw spectral characteristics of a sample on a basis of any variation between the known spectral characteristic and detected calibration spectral characteristics.
18. The emission spectrometer according to claim 17 wherein the drift calibration system comprises: a standard sample which when radiated by the energy beam emits radiation of known spectral characteristics; and, a first optical system movable between: a drift calibration position where the first optical system is operable to divert the energy beam to the standard sample and receive and subsequently direct radiation for the standard sample arising from irradiation by the energy beam to the detector; and, a measurement position where the first optical system is outside of the measurement optical path.
19. The emission spectrometer according to claim 18 wherein the drift calibration system is operable to vary a point of incidence of the energy beam on the standard sample on subsequent operations of the drift calibration system.
20. The emission spectrometer according to claim 19 wherein the drift calibration system comprises an X-Y translation device on which the standard sample is mounted wherein the translation device is capable of moving the standard sample in a plane in one or both of an X and Y direction on subsequent operations of the drift calibration system.
21. The emission spectrometer according to claim 17 wherein the drift calibration system comprises a radiation source of known spectrum and a second optical system operable for directing the radiation from the radiation source of known spectrum to the detector.
22. The emission spectrometer according to claim 21 wherein the second optical system defines an optical path for the radiation source and is movable to a position where the radiation from the radiation source is in a field of view of the detector.
23. The emission spectrometer according to claim 17 wherein the drift calibration system comprises a processor capable of generating drift data on a basis of a comparison between one or both of (a) known spectral characteristics of the standard sample; and, spectral characteristics of radiation emitted from the standard sample as detected by the detector when the standard sample is irradiated by the energy beam; and (b) a known spectrum of a radiation source; and, the spectrum of the radiation source as detected by the detector.
24. The emission spectrometer according to claim 23 wherein the drift calibration system is capable of generating an alarm when a difference between the known spectral characteristics of the standard sample and spectral characteristics of radiation emitted from the standard sample as detected by the detector when the standard sample is irradiated by the energy beam is greater than a threshold level.
25. The emission spectrometer according to claim 23 or 24 wherein the drift calibration system is capable of generating an alarm when a difference between the known spectrum of the radiation source; and, the spectrum of the radiation source as detected by the detector is greater than a threshold level.
26. The emission spectrometer according to any one of claims 17 to 25 comprising an energy level monitor capable of monitoring an energy level of the energy beam and providing a signal to the drift calibration system indicative of the monitored energy level.
27. The emission spectrometer according to claim 26 wherein the spectrometer is capable of generating an alarm when the monitored energy level is below a threshold energy level.
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| US61/436,328 | 2011-01-26 | ||
| PCT/AU2012/000016 WO2012100284A1 (en) | 2011-01-26 | 2012-01-11 | An emission spectrometer and method of operation |
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| CN107037012B (en) * | 2017-04-05 | 2019-10-25 | 华中科技大学 | Echelle spectrometer dynamic correcting method for laser induced breakdown spectroscopy acquisition |
| CN115839943B (en) * | 2023-02-13 | 2023-07-11 | 合肥金星智控科技股份有限公司 | Laser-induced spectrum system, spectrum calibration method and electronic equipment |
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| US7321424B2 (en) * | 2004-08-05 | 2008-01-22 | Acton Research Corp. | Self-referencing instrument and method thereof for measuring electromagnetic properties |
| US7502105B2 (en) * | 2004-09-15 | 2009-03-10 | General Electric Company | Apparatus and method for producing a calibrated Raman spectrum |
| US7994479B2 (en) * | 2006-11-30 | 2011-08-09 | The Science And Technology Facilities Council | Infrared spectrometer |
| CN101689222B (en) * | 2007-05-07 | 2012-12-26 | 真实仪器公司 | Calibration of a radiometric optical monitoring system used for fault detection and process monitoring |
| CN101354287B (en) * | 2007-07-24 | 2010-12-22 | 杭州远方光电信息有限公司 | Spectrometer and method for correcting the same |
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