Spark stand assembly for optical emission spectroscopy instrument

Abstract

To provide a spark stand assembly that facilitates a secure and robust manner of ensuring the gas-tightness of a plasma chamber.SOLUTION: A spark stand assembly 120 for an optical emission spectroscopy (OES) instrument is provided which comprises: a spark stand body 121 attached to a mounting flange 122 that makes it possible to attach the spark stand assembly to a main housing of the OES instrument; an exciter 123a disposed in a recess arranged on a top surface of the spark stand body; and an elevated portion arranged on the top surface of the spark stand body 121 adjacent to the mounting flange. The recess on the top surface of the spark stand body forms an optical transmission path from the plasma chamber to the passageway, and a notch 125 forms a part of the optical transmission path from the plasma chamber to the passageway.SELECTED DRAWING: Figure 3A

Description

[Technical field]

[0001] Exemplary and non-limiting aspects of the present invention relate to optical emission spectroscopy instruments, and in particular to spark stand assemblies for such instruments. [Background technology]

[0002] Analyzer devices applicable to the analysis of materials such as metals with high accuracy typically rely on optical emission spectroscopy (OES) technology. Analyzer devices relying on spark OES techniques find use in laboratories as well as industries where accurate and reliable material analysis is important. High performance spark OES devices targeted for commercial industrial applications are complex devices that are typically provided as desktop (or bench-top) devices, or are provided with wheels or are mobile devices mounted on wheeled trolleys adapted for transporting the analyzer.

[0003] The basic working principle of OES techniques involves exciting the sample with suitable excitation means to convert the fraction of the sample into a plasma state, and transmitting the light emitted from the transitions between the energy levels of the excited atoms or ions of the plasma to a spectrometer for analysis of the elemental composition of the sample through comparison of the captured sample spectrum with respective reference spectra of one or more samples of known elemental composition. Various excitation means are known, such as arc, spark, laser, inductively coupled plasma (ICP) and direct current plasma (DCP), in which case the type of excitation is often applied to designate the respective OES technique, e.g. spark OES or laser-induced breakdown spectroscopy (LIBS).

[0004] Depending on the wavelength range to be covered by the optical system of the OES apparatus, an ultraviolet (UV) transparent atmosphere may be required in the optical system and along the transmission path from the spot of plasma generation to the spectrometer interface. The atmosphere, particularly at and near the spot of plasma generation, typically contains an inert gas such as argon, which facilitates plasma generation and prevents the formation of undesirable materials such as oxides, carbides and nitrides that tend to form when plasma is generated in the atmosphere.

[0005] Due to this requirement of a specific atmosphere at and near the spot of plasma generation, the OES apparatus typically includes a plasma chamber with an opening for exposing a spot of a sample placed against the opening for excitation, while placing the sample in the opening typically seals the plasma chamber in a gas-tight manner. The plasma chamber further includes an excitation means for exciting the exposed spot of the sample, a gas inlet that allows injecting an inert gas into the chamber to purge the spot of plasma generation, and an outlet for removing the inert gas formed during plasma generation and debris formed during plasma generation from the plasma chamber. The plasma chamber is further provided with an (optical) window for transmitting the light emitted from the plasma out of the plasma chamber to a spectrometer. In OES apparatus that utilize spark excitation (i.e., spark OES apparatus), the plasma chamber may also be referred to as a spark chamber.

[0006] Without loss of generality, an element of an OES apparatus that includes a plasma chamber (e.g., a spark chamber) may be referred to as a spark stand. The spark stand typically further comprises an excitation means, a gas injection means for injecting an inert gas into the plasma chamber via a gas inlet, an exhaust means for transmitting the inert gas and debris from the plasma chamber via an outlet, and a transmission path for transmitting light emitted from the plasma through an optical window of the plasma chamber towards a spectrometer. An opening to the plasma chamber is typically provided as an opening through the housing of the spark stand, such that a sample may be provided for measurement by positioning it against the opening through the housing of the spark stand.

[0007] The spark stand may be provided as a separate element from the main housing of the OES device, including, for example, the spectrometer, and may be attached to the main housing in a fixed manner or may be removable from the main housing. The latter approach allows for an approach in which the spark stand can be attached to the main housing of the OES device to perform measurements of a sample and removed from the main housing for cleaning and / or maintenance. Regardless of the type of attachment of the spark stand to the main housing of the OES device (fixed or removable), the spark stand may be provided with a mounting flange that serves as an "interface" between the spark stand and the main housing of the OES device, in which case the transmission paths provided in the spark stand are coupled via the mounting flange to the transmission paths provided in the main housing and further to the spectrometer provided in the main housing. Furthermore, electrical connections to the main housing of the OES device that may be necessary for the operation of certain components of the spark stand may be arranged through the mounting flange as well.

[0008] Important properties of the spark stand include ensuring gas-tightness of the plasma chamber contained therein and providing reliable and robust controlled transmission of light from the plasma generated in the plasma chamber to the spectrometer via a transmission path therein, so that any improvement in this regard will help to further improve the accuracy and reliability of analysis of the elemental composition of a sample via operation of an OES apparatus utilizing the spark stand. Summary of the Invention

[0009] It is an object of the present invention to provide a spark stand assembly that facilitates a reliable and robust method of ensuring gas tightness of a plasma chamber. Additionally or alternatively, it is an object of the present invention to provide a spark stand assembly that facilitates controlled transmission of light from a plasma generated in a plasma chamber to a spectrometer.

[0010] According to one embodiment, a spark stand assembly for an optical emission spectroscopy (OES) device is provided, the spark stand assembly comprising: a spark stand body attached to a mounting flange enabling mounting of the spark stand assembly to a main housing of an OES device; an exciter disposed in a recess disposed in a top surface of the spark stand body; a ridge disposed in the top surface of the spark stand body adjacent the mounting flange; an elongated notch disposed in the top surface of the spark stand body and connecting to a passage passing through the recess; a spark stand plate removably attachable to the top surface of the spark stand body to cover the recess, the notch and at least a portion of the ridge forming a plasma chamber, the notch forming a portion of an optical transmission path from the plasma chamber to the passage, an opening arranged such that when the spark stand plate is attached to the top surface of the spark stand body, the opening is spatially aligned with the exciter; and a seal member disposed between the top surface of the spark stand body and the spark stand plate, surrounding the recess and the notch and routed to the ridge.

[0011] In one example, a seal member groove is disposed on a top surface of the spark stand body and on a ridge such that it surrounds the recess and the notch, and the seal member is at least partially embedded in the seal member groove. In another example, a seal member groove is disposed on a surface of the spark stand plate facing the spark stand body, and a seal member is at least partially embedded in the seal member groove, and the seal member groove is disposed such that when the spark stand plate is attached to the top surface of the spark stand body, the seal member surrounds the recess and the notch and is disposed on the ridge.

[0012] According to another embodiment, there is provided an OES apparatus comprising a main housing and a spark stand assembly according to the exemplary embodiment above, the main housing comprising an optical spectrometer assembly and a mounting interface for mounting the spark stand assembly to the main housing, the mounting interface comprising an optical interface for connecting the optical transmission path of the spark stand assembly to the spectrometer assembly.

[0013] The exemplary embodiments of the invention presented in this patent application should not be construed as bringing about limitations on the applicability of the claims. The verb "to comprise" and its derivatives are used in this patent application as an open limitation that does not exclude the presence of unrecited features. The features described below are freely combinable with each other unless expressly specified otherwise.

[0014] Certain features of the invention are set forth in the appended claims. However, the invention in its various aspects, both as to its structure and its method of operation, together with further objects and advantages thereof, will best be understood from the following description of certain embodiments when read in connection with the accompanying drawings.

[0015] Embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 illustrates a schematic diagram of an optical emission spectroscopy (OES) apparatus according to one example. [Diagram 2] FIG. 2 illustrates a block diagram of certain elements of an OES device according to one example. [Figure 3A] FIG. 3A illustrates a schematic diagram of a spark stand assembly according to an example. [Figure 3B] FIG. 3B illustrates a schematic diagram of a spark stand assembly according to an example. [Figure 3C] FIG. 3C illustrates a schematic diagram of a spark stand assembly according to an example. [Figure 4] FIG. 4 illustrates a schematic of a sample positioned for measurement via use of a spark stand assembly according to one example. [Diagram 5] FIG. 5 illustrates generally certain details of a spark stand assembly according to an example. [Figure 6A] FIG. 6A illustrates generally certain details of a spark stand assembly according to an example. [Figure 6B] FIG. 6B illustrates generally certain details of a spark stand assembly according to an example. [Figure 6C] FIG. 6C illustrates generally certain details of a spark stand assembly according to an example. [Figure 6D] FIG. 6D illustrates generally certain details of a spark stand assembly according to an example. [Figure 6E] FIG. 6E diagrammatically illustrates certain details of a spark stand assembly, according to an example. [Figure 6F] FIG. 6F diagrammatically illustrates certain details of a spark stand assembly according to an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] FIG. 1 shows a schematic diagram of an example OES device 100, including a main housing 110 of the OES device 100 and a spark stand assembly 120 attached to the main housing 110. The spark stand assembly 120 may be attached to the main housing 110 to perform measurements on one or more samples, and may be removed from the main housing 110 for cleaning and / or maintenance. In other words, the spark stand assembly 120 may be removably attached to the main housing 110. FIG. 2 shows a block diagram of certain (logical) elements of an example OES device 100, including a controller 112, an exciter 123, a light spectroscopic detection assembly 114, and a user interface (UI) 116. The OES device may be suitable for analysis of any sample having a conductive surface, such as a sample that includes or consists of a metal.

[0018] The main housing 110 serves to house one or more components of the OES device 100, and the main housing 110 may further include storage space for, for example, accessories and / or materials applicable for operating the OES device 100. In this regard, the main housing 110 may include a mounting interface for mounting the spark stand assembly 120 that allows for mechanical mounting between the spark stand assembly 120 and the main housing 110 and provides an optical and electrical interface between components of the spark stand assembly 120 and components provided on or coupled to the main housing 110. The main housing 110 may include (or be coupled to) a UI 116 for operating at least certain aspects of the OES device 100, where the UI 116 may include one or more user input devices (such as a keyboard, mouse, touch panel, touch screen, an arrangement of one or more keys, buttons, switches, etc.) for providing user input for controlling various aspects related to the operation of the OES device 100, and a display device for displaying information to a user, such as information regarding the operational status of the OES device 100 and measurement results. The OES device 100 may enable analysis of the elemental composition of a sample using one or more OES techniques, such as spark OES and / or arc OES.

[0019] The main housing 110 further comprises an optical spectroscopic detection assembly 114 including an optical spectrometer 114a and an optical detector assembly 114b, whereas the main housing 110 further provides a first transmission path optically coupling the optical interface of the mounting interface to the optical spectrometer 114a of the optical spectroscopic detection assembly 114, thus enabling the transmission of light received from the spark stand assembly 120 via the optical interface of the mounting interface to the optical spectroscopic detection assembly 114. The optical spectrometer 114a can separate the light received via the optical detector interface into a set of wavelengths, whereas the optical detector assembly 114b can generate one or more measurement signals describing the relative light intensity of the optical emission spectrum at different wavelengths, which may appear, for example, as one or more emission peaks at each wavelength. In this regard, by way of example, the optical detector assembly 114b can comprise an optical detector array including a plurality of optical detectors, such as an array of photomultiplier tubes mounted behind respective rectangular apertures that pass only narrow wavelength bands. According to another example, the light detection assembly 114b can include an image sensor, which can be provided as a charge-coupled device (CCD), a complementary metal-oxide semiconductor (CMOS) sensor, or in general, any (silicon-based) solid-state sensor, whereby the light detection assembly 114b substantially captures one or more images of the dispersed light received from the optical spectrometer 114a.

[0020] The main housing 110 may further comprise a controller 112 communicatively coupled to the UI 116 and the optical detection assembly 114b of the optical spectroscopic detection assembly 114, allowing for the transfer of control information and data (such as measurement results) between the controller 112 and the UI 116, and allowing the controller 112 to receive one or more measurement signals from the optical detection assembly 114b. The controller 112 may further be communicatively coupled to an electrical interface of the mounting interface, which allows for electrical coupling to an exciter 123 provided on the spark stand assembly 120 when mounted to the main housing 110 via the mounting interface, thereby allowing activation of the exciter 123 via operation of the controller 112. The respective communication couplings between the controller 112 and the UI 116, and between the controller 112 and the electrical interface of the mounting interface may be provided using respective electrical signals carried via respective one or more electrical wires, for example.

[0021] As a specific example of the operation of the OES apparatus 100, the controller 112 may perform a measurement procedure to determine at least certain aspects of the elemental composition of the sample under study, the measurement procedure may be performed in response to a trigger signal that may be received in response to a user operating the UI 116 accordingly. The measurement procedure may include the controller 112 activating the exciter 123 for a predetermined time to generate excitation that converts fractions of the sample under study into a plasma state, recording one or more measurement signals generated at the optical detection assembly in response to light emitted from the plasma and received at the optical detection assembly 114b via the optical spectrometer 114a, and performing an analysis of the elemental composition of the sample under study based on the one or more recorded measurement signals (e.g., via comparison to respective reference spectra of one or more samples of known elemental composition). Measurement procedures of the types described above are well known in the art and will be outlined herein for completeness of explanation.

[0022] 3A-3C are schematic diagrams illustrating certain components of a spark stand assembly 120, according to one example. The components illustrated in FIG. 3A include a spark stand body 121 mounted to a mounting flange 122, an electrode 123a as an exciter 123 disposed in a recess formed in an upper surface of the spark stand body 121, a raised portion 124 disposed on the upper surface of the spark stand body 121 adjacent the mounting flange 122, an elongated notch 125 disposed on the upper surface of the spark stand body 121, the elongated notch 125 connecting the recess to a path through the raised portion 124, and a seal member groove 126 disposed on the upper surface of the spark stand body 121, the seal member groove 126 surrounding (e.g., around) the recess and routed beyond the raised portion 124. The mounting flange 122 is provided with an opening therethrough that is aligned with the path through the raised portion 124 and the elongated notch 125. The seal member groove 126 is positioned to receive a seal member 127 (not shown in the illustration of FIG. 3A but shown in the illustration of FIG. 3C ), such as a sealing ring (e.g., an O-ring) made of a resilient material. The spark stand assembly 120 may further include a seal member 127 at least partially embedded in the seal member groove 126. The cross-section of the seal member groove 126 may have a shape that facilitates retaining the seal member 127 in place once disposed therein.

[0023] The top surface of the spark stand body 121 is positioned for receipt of a spark stand plate 130 that covers at least the recess, the elongated notch 125, and at least a portion of the ridge 124. As an example in this regard, the illustration of Figure 3B shows a schematic perspective view of the spark stand assembly 120 with the spark stand plate 130 mounted over the top surface of the spark stand body 121. In contrast, Figure 3C shows a cross-section of the spark stand assembly 120 with the spark stand plate 130 mounted over the top surface of the spark stand body 121. The spark stand plate 130 is removably attached to the upper surface of the spark stand body 121 through the use of an attachment mechanism provided to hold (e.g., press) the spark stand plate 130 against the upper surface of the spark stand body 121, as depicted in each of Figures 3A-3C, by a set of clamps 128 that secure the spark stand plate 130 to the upper surface of the spark stand body 121 and allow for the release of the spark stand plate 130 from the spark stand body 121.

[0024] When mounted on the top surface of the spark stand body 121, the spark stand plate 130 covers the recesses so that a plasma chamber is formed and covers the notches 125 so that a second transmission path is formed. The second transmission path provides a view to the plasma (to be) generated in the plasma chamber from the opening through the mounting flange 122, and thus the second transmission path allows the transmission of light from the plasma via the notches 125, via a path through the ridges 124, and further via the opening through the mounting flange 122 to the optical interface of the mounting interface provided in the main housing 110. In this regard, the surface of the spark stand plate 130 intended to face the top surface of the spark stand body 121 may be referred to as the inner surface or spark stand body facing surface, while the opposite surface of the spark stand plate 130 may be referred to as the outer surface. The inner surface of the spark stand plate 130 may have a shape substantially corresponding to the shape of the top surface of the spark stand body 121, away from the recesses and notches 125 located therein. In this regard, by way of example, the top surface of spark stand body 121 may be substantially planar apart from the recesses, notches 125 and seal member grooves 126 disposed therein, and ridges 124 disposed thereon, whereas the inner surface of spark stand plate 130 may be substantially planar apart from the portions for abutting ridges 124 against the top surface of spark stand body 121. Thus, the portion of spark stand plate 130 intended to face ridges 124 on the top surface of spark stand body 121 may have a shape that substantially corresponds to the shape of ridges 124, thereby accommodating ridges 124 when spark stand plate 130 is correctly positioned relative to the top surface of spark stand body 121.

[0025] The spark stand plate 130 includes an opening 131 therethrough, which is substantially spatially aligned with the electrode 123a when the spark stand plate 130 is fixed in its position on the upper surface of the spark stand body 121. In this regard, spatial alignment means that the projection of the opening 131 along a line perpendicular to the surface of the spark stand plate 130 surrounds the tip of the electrode, e.g., such that the tip of the electrode is approximately in the center of the projection. Furthermore, when the spark stand plate 130 is fixed in its position on the upper surface of the spark stand body 121, the seal member 127 facilitates sealing the recess located in the spark stand body 121 and the notch 125 away from the opening 131 through the spark stand plate 130 in a gas-tight manner, thereby forming the plasma chamber and the aforementioned optical path.

[0026] When operating the spark stand assembly 120 as part of the operation of the OES apparatus 100, the sample 140 may be positioned on the spark stand plate 130 such that the sample 140 covers the aperture 131, as illustrated diagrammatically in FIG. 4. In this regard, the sample 140 positioned at the aperture 131 seals the plasma chamber in a gas-tight manner while exposing a portion of the sample 140 at the location of the aperture 131 for generating excitation via activation of the electrode 123a. This allows for plasma to be generated at a surface of the sample 140 via activation of the electrode 123a. The gas-tight seal may be facilitated by suitable preparation (e.g., grinding or milling) of the sample 140 and / or by placement of the sample 140 in the aperture via sealing of the aperture 131 and / or application of an adapter element that ensures correct placement of the sample 140 relative to the aperture 131. Gas sealing of the plasma chamber during the measurement procedure is generally advantageous in terms of measurement reliability and repeatability, but on the other hand can be a crucial property for detecting specific elements such as nitrogen or oxygen, as well as for measurements where a UV-transparent atmosphere is created via injection of an inert gas (such as argon) into the plasma chamber.

[0027] As mentioned above, when covered by the spark stand plate 130, the elongated notch 125 on the top surface of the spark stand body 121 serves as part of a second transmission path disposed via a path through the ridge 124. Thus, the ridge 124 disposed adjacent to and with a path therethrough on the mounting flange 122 can be considered as a bridge structure disposed on the top surface of the spark stand body 121. When the spark stand assembly 120 is mounted on the main housing 110, the second transmission path disposed on the spark stand assembly 120 is aligned with the first transmission path disposed on the main housing 110, thereby forming a transmission path that allows light emitted from the plasma to be transmitted to the optical spectroscopic detection assembly 114 substantially along a plane that is parallel to the top surface of the spark stand body 121 and the inner surface of the spark stand plate 130, thereby providing a substantially 0° (i.e., zero degree) viewing angle with respect to the plasma.

[0028] The elongated notch 125 disposed on the upper surface of the spark stand body 121 may have a depth that varies with distance from a recess that forms a plasma chamber when the spark stand plate 130 is disposed on the upper surface of the spark stand body 121. As an example in this regard, the depth of the notch 125 may steadily decrease from a first end of the notch 125 in the recess to a second end of the notch 125 in the path through the ridge 124, where the bottom of the notch 125 at its first end may be substantially aligned with the bottom of the recess. Such a shape of the notch 125 may facilitate the removal of contaminants and / or debris generated in the course of the measurement from the notch 125 and / or from the recess via injection of a flow of inert gas. According to one example, the cross section of the notch may have a shape (e.g., U-shaped or V-shaped) that narrows toward the bottom of the notch 125, which may likewise facilitate the removal of contaminants and / or debris from the notch 125 and / or the recess via injection of a flow of inert gas.

[0029] The transmission path may include a window or coupling lens arranged such that a view from the optical spectroscopic detection assembly 114 to the plasma is provided through the window or coupling lens. In the following, this aspect is described through an example including a coupling lens arranged in the transmission path, while the description is easily applicable to another example in which a window is applied instead, but with differences. The coupling lens may be arranged at a selected position along the transmission path from the plasma chamber to the entrance aperture, for example, at a suitable position of the first transmission path, or at a suitable position of the second transmission path (e.g., in the path through the ridge 124), at the mounting interface (in the main housing 110), or at a selected position of the aperture through the mounting flange 122. The coupling lens may function to form an image of the plasma at a selected location with respect to the entrance aperture to the optical spectrometer 114a (e.g., at the optical spectrometer 114a, the entrance aperture to the optical spectrometer 114a, or at the first transmission path) to prevent contamination and / or debris resulting from plasma generation during measurements entering the optical spectroscopic detection assembly 114, and to isolate the transmission path, and thus at least a portion of the optical spectroscopic detection assembly 114, from the plasma chamber. The characteristics and / or location of the coupling lens (along the transmission path) may be selected, for example, taking into consideration the respective characteristics and dimensions of the first transmission path, the second transmission path, and the optical spectroscopic detection assembly 114. Typically, it is advantageous to position the coupling lens as far away from the plasma chamber as possible to reduce the amount of contamination and / or debris filling the plasma chamber-facing surface of the coupling lens.

[0030] The use of spark stand plate 130 that is removably attached to spark stand body 121 is advantageous in that it allows the plasma chamber and notch 125 to be exposed for cleaning between measurements, e.g., to remove debris and / or contaminants that inevitably accumulate on the respective surfaces of the plasma chamber, notch 125 and coupling lens during the course of measurements performed using spark stand assembly 120.

[0031] The mounting flange 122 allows for the attachment of the spark stand assembly 120 to the main housing 110 of the OES device 100 via a mounting interface provided in the main housing 110 in a removable manner, i.e., such that the spark stand assembly 120 can be removed from the main housing 110 for maintenance and cleaning, and (re)attached to the main housing 110 for subsequent measurements. In this regard, the mounting flange 122 and / or the mounting interface of the main housing 110 can be provided with a user-operable attachment mechanism that allows for the spark stand assembly 120 to be secured to the main housing 110 such that a precise spatial alignment between the spark stand assembly 120 and the main housing 110 is provided, and such that the spark stand assembly 120 can be released from the main housing. In this regard, the term mounting flange 122 will be broadly interpreted to essentially encompass any "interface element" that is removably attachable to a mounting interface of the main housing 110 of the OES device 100.

[0032] The spark stand body 121 and the spark stand plate 130 may be made from a durable material capable of withstanding the heat resulting from the plasma generated in the plasma chamber. Examples of suitable materials include metals such as stainless steel (e.g., EN 1.4305, EN 1.4301, EN 1.0050, EN 1.0760 or EN 2.0376). The spark stand body 121 is attached to the mounting flange 122 such that the top surface of the spark stand body 121 lies substantially horizontal when the spark stand assembly 120 is attached to the main housing 110 of the OES device 100 when the OES device 100 is in its operating position. Typically, but not necessarily, the mounting flange 122 is made from the same or a similar material as the spark stand body 121.

[0033] In the example using the electrode 123a as the exciter 123 in the example of Figures 3A-3C, the electrode 123a may be applied to generate spark excitation under the control of the controller 112, while in other examples the exciter 123 may apply other excitation techniques known in the art for plasma generation. The electrode 123a may be positioned relative to the spark stand body 121 such that a tip of the electrode 123a resides inside a plasma chamber formed between a recess disposed on the upper surface of the spark stand body 121 and a spark stand plate 130 disposed thereon, while the remaining part of the electrode 123a may be embedded within the spark stand body 121. In this regard, the electrode 123a may be attached to the spark stand body 121 via an insulating arrangement (e.g., an insulating sleeve) that may be made of a suitable ceramic material. As an example in this regard, the insulating arrangement may comprise a sheath of ceramic material surrounding the electrode 123a such that the tip of the electrode 123a is exposed in a recess provided in the upper surface of the spark stand body 121, while the "top" end of the sheath may serve as the "bottom" of the recess forming the plasma chamber. In other words, the tip of the electrode 123a may be brought into the recess forming the plasma chamber through an opening provided in the insulating arrangement.

[0034] When the electrode 123a is activated to generate a plasma on the surface of the sample 140 exposed through the opening 131 through the spark stand plate 130, a plasma is generated between the tip of the electrode 123a and the surface of the sample 140. In this regard, FIG. 5 shows a schematic cross-sectional view of selected details of an example spark stand assembly 120 and illustrates a cone-shaped plasma 132 formed upon activation of the electrode 123a between the tip of the electrode 123a exposed through the opening 131 through the spark stand plate 130 and the surface of the sample 140. As a result, light emitted from the cone-shaped plasma 132 is transmitted through a second transmission path formed in the spark stand assembly 120, towards the opening, through the mounting flange 122, and further through a first transmission path in the main housing 110 to the optical spectroscopic detection assembly 114.

[0035] An airtight seal of the notch 125 and the recess of the top surface of the spark stand body 121 via the placement of the spark stand plate 130 thereon can be ensured via the seal member 127, which can be at least partially embedded in the seal member groove 126 when the spark stand plate 130 is pressed against the top surface of the spark stand body 121 by a mounting mechanism such as a set of clamps 128. In this regard, the routing of the seal member groove 126, i.e. the seal member 127, on the bridge structure formed by the ridge 124 provides a placement, pressing the spark stand plate 130 against the top surface of the spark stand body 121, sufficient to ensure a gas seal of both the plasma chamber and the notch 125, which serves as part of a second transmission path from the plasma chamber towards the optical interface of the mounting interface of the main housing 110 of the OES apparatus 100. In contrast to this, in previously known solutions, separate seal rings are typically applied between a first surface of the spark stand plate and the top surface of the spark stand body to seal the plasma chamber, and between a second surface of the spark stand plate 130 (which is substantially perpendicular to the first surface) and a mounting flange that seals the optical path from the plasma chamber towards the optical interface of the mounting interface, thereby sealing the spark stand plate separately against two surfaces that are substantially perpendicular to each other. This in turn requires the correct positioning of the spark stand plate in two directions that are substantially perpendicular to each other, which is a tedious procedure that poses a risk of compromising the seal, and also leads to wear and possible damage to the seal rings with repeated mounting and dismounting of the spark stand plate.

[0036] Along the aforementioned lines, according to one example, the inner surface of the spark stand plate 130 may be substantially planar apart from the portion intended to abut the ridge 124 when the spark stand plate 130 is mounted on the spark stand body 121. As a result, the second transmission path from the conical plasma 132 towards the opening through the mounting flange 122 is essentially partially impeded due to the non-zero thickness of the portion of the spark stand plate 130 covering the notch 125 when the spark stand plate 130 is positioned on the top surface of the spark stand body 121, as also shown in the schematic diagram of FIG. 5. Conversely, the non-zero thickness of the spark stand plate 130 partially blocks the view from the opening to a small portion of the conical plasma 132 through the mounting flange 122, which may be referred to as the inherent masking (non-zero thickness) provided by the spark stand plate 130. Nonetheless, due to the relatively small thickness of the spark stand plate 130, such a configuration allows transmission of light emitted from the conical plasma 132 substantially throughout the entire height of the conical plasma 132 along the central axis (coincident with line A shown in FIG. 5 ) via the optical interface of the mounting interface, via a first transmission path toward the optical spectroscopic detection assembly 114, and via a second transmission path.

[0037] In certain scenarios, it has proven beneficial to be able to control the visibility from the optical spectroscopic detection assembly 114 to a given portion of the conical plasma 132 so as not to transmit light emitted from the respective portion of the conical plasma 132 to the optical spectroscopic detection assembly 114. In this regard, the volume of the conical plasma 132 provides a good approximation of the available intensity of the conical plasma 132. The geometric characteristics of the conical plasma 132 are such that the majority of its volume is near its base immediately adjacent to the sample 140 located at the aperture 131 through the spark stand plate 130. Thus, a noticeable amount of light emitted from the conical plasma 132 can be masked by masking a relatively small portion of the height of the conical plasma 132. Particularly for a substantially 0° viewing angle to the conical plasma 132, such masking can be achieved by utilizing the temperature distribution related characteristics of the conical plasma 132. In this regard, an aspect of particular interest involves the temperature gradient of the plasma along the central axis of the conical plasma 132 (line A in the diagram of FIG. 5) between the tip of the electrode 123a and the surface of the sample 140 exposed to excitation through the opening 131 via the plasma stand plate 130. In this regard, the temperature distribution of the conical plasma 132 is shown via isotherms (shown as respective dashed lines) that are substantially parallel to the base of the conical plasma 132 (and thus substantially perpendicular to the central axis of the conical plasma 132). The base and the portion of the conical plasma 132 close to the base are the hottest regions, while the temperature of the plasma 132 decreases towards the tip of the conical plasma 132 (and thus towards the tip of the electrode 123a), with the temperature of the base (apparently) exceeding 12000 degrees Celsius, while the temperature of the tip (apparently) falling below 3400 degrees Celsius. The height of the conical plasma 132 is substantially equal to the distance between the tip of the electrode 123a and the outer surface of the spark stand plate 130 (i.e., the surface of the sample 140 placed on the outer surface at the position of the opening 131), while the diameter of the base of the conical plasma 132 may be substantially equal to the height of the conical plasma 132.

[0038] In certain scenarios, masking of the hottest part of the conical plasma 132 may be advantageous in terms of accuracy and reliability of the measurement procedure. Ion spectral lines and thermal background radiation mainly originate from the hottest part of the conical plasma 132 closest to the surface of the sample 140, since the amount of energy to excite these spectral lines is only available in this part of the conical plasma 132. Since ion spectral lines and thermal background radiation are typically considered as disturbing aspects of the analysis performed by the OES device 100, masking of the conical plasma 132 such that light emitted from the hottest part is prevented from being transmitted to the optical spectroscopic detection assembly 114 via the second transmission path may be advantageous. Such masking may be particularly useful in measurements aimed at detecting specific elements such as carbon, phosphors and sulfur in iron or nickel matrices, since it allows for example to mask perturbing ionization lines originating from the conical plasma 132 volume near the surface of the sample 140, thus eliminating spectral interferences that arise without masking, with insufficient masking or through the application of plasma viewing angles larger than 0 degrees. The excitation parameters applied in activating the electrode 123a may vary from matrix to matrix, such that, for example, an aluminum alloy requires different excitation parameters (e.g., different excitation energies) than a steel or titanium alloy, due to the different melting points of these materials. When a higher excitation energy is supplied via the electrode 123a, the temperature distribution of the conical plasma 132 changes as the temperature at the surface of the sample 140 increases with increasing excitation energy, thereby shifting the respective positions of the isotherms along the axis A. Thus, different matrices requiring different excitation energies from the electrode 123a also require different amounts of masking in order to eliminate perturbing spectral lines with excitation characteristics that do not change with the applied excitation energy.

[0039] Along the lines mentioned above, while the inherent masking provided by any, relatively small thickness of the rim of the opening 131 through the spark stand plate 130 may not have a substantial effect in terms of obstructing the line of sight to the conical plasma 132, true spatial masking of the conical plasma 132 can be achieved by providing the spark stand plate 130 with a spatial mask that protrudes from its inner surface. Here, the spatial mask is located in a portion of the spark stand plate 130 that spatially coincides with the notch 125 when the spark stand plate 130 is fixed in its position in the spark stand body 121. As a result, the spatial mask can be applied to partially block the second transmission path between the plasma chamber and the opening through the mounting flange 122, thereby partially blocking the line of sight from the optical spectroscopic detection assembly 114 to the conical plasma 132 that is (should be) generated in the plasma chamber, and in particular to the hottest portion of the conical plasma 132 at and near its base. The extent of the spatial masking provided depends on the shape and size of the spatial mask, and the extent of the masking may be defined via the height (or depth) of the spatial mask measured from the outer surface of the spark stand plate 130. The height (or depth) of the spatial mask may be referred to as the masking height (or masking depth). The masking height (or masking depth) may be defined via a predefined percentage of the distance between the tip of the electrode 123a and the outer surface of the spark stand plate 130. As a non-limiting example, the predefined percentage may be a value selected from the range of 25% to 70%, for example 50%. However, the most appropriate masking height (or masking depth) may be selected according to the circumstances, for example taking into account the excitation parameters applied in activating the electrode 123a.

[0040] According to an example, the excitation parameters may be selected in dependence of the matrix and / or of the analytical subprogram applied for the measurement. An example in this respect is provided for the difference between an iron matrix (Fe matrix) and an aluminum matrix (Al matrix). On the one hand, a set of optimized excitation parameters may be applied to a relatively wide range of different materials, while certain materials may require dedicated excitation parameters due to their metallurgical properties. For example, when determining the phosphor content in an aluminum alloy, such material-dependent properties may need to be taken into account, since the phosphor lines (P lines) may be superimposed by continuous background radiation originating from the volume of the conical plasma 132 close to the surface of the sample 140. However, in the case of an aluminum matrix sample, this volume of the conical plasma 132 extends further away from the surface of the sample 140 (along the central axis of the conical plasma 132) than in the case of an iron matrix sample, and therefore a higher degree of spatial masking is required to eliminate the spectral background in the case of an aluminum matrix sample than in the case of an iron matrix sample.

[0041] As an example of providing the spatial mask on the spark stand plate 130, Fig. 6A shows a schematic of the spark stand plate 130 with a masking portion 133a provided as an integral part of the spark stand plate 130 and functioning as a spatial mask. The masking portion 133a can consist of a protrusion extending from an inner surface of the spark stand plate 130 provided on a portion of the spark stand plate 130 that spatially coincides with the notch 125 when the spark stand plate 130 is fixed in its position on the spark stand body 121. In other words, the masking portion 133a can be considered as a thickened portion or a thickened area of ​​the spark stand plate 130 located on a portion of the spark stand plate 130 that spatially coincides with the notch 125 when the spark stand plate 130 is fixed in its position on the spark stand body 121. As a result, when the spark stand plate 130 is placed on the upper surface of the spark stand body 121, the masking portion 133a can protrude into the notch 125 located on the upper surface of the spark stand body 121, thereby acting as a spatial mask that partially blocks the view (from the opening through the mounting flange 122) into the conical plasma 132.

[0042] Fig. 6B shows diagrammatically a spatial mask provided as masking portion 133a according to another example, where masking portion 133a provides a higher masking height (or masking depth) compared to that of the example of Fig. 6A. Figs. 6C and 6D show respectively further examples of providing a spatial mask as masking portion 133a at respective masking heights (or masking depths), where masking portion 133a has a shape different from that of the respective examples of Figs. 6A and 6B.

[0043] In one example, the spark stand assembly 120 may be provided with two or more spark stand plates, in which case the spark stand plate applied for a certain measurement may be selected in view of the (expected) properties of the sample 140 under study. In this regard, as an example, the two or more spark stand plates may comprise a first spark stand plate provided without a spatial mask and a second spark stand plate provided with a spatial mask, so that the first and second spark stand plates can be used interchangeably, for example, such that the second spark stand plate is applied for measurements in which masking of the hottest parts of the conical plasma 132 is considered to be advantageous, and the first spark stand plate 130 is applied for measurements in which such masking is considered to be unnecessary or disadvantageous. In a variation of this example, the two or more spark stand plates can include two or more second spark stand plates each provided with a spatial mask having a masking height (or masking depth) different from the respective masking heights (or masking depths) of the others of the two or more spark stand plates.

[0044] In another example, the two or more spark stand plates of the spark stand assembly 120 may comprise a first spark stand plate provided with a spatial mask providing a first masking height (or masking depth) and a second spark stand plate providing a second spatial mask having a second masking height (or masking depth) different from the first masking height (or masking depth) of the first spark stand plate (e.g., according to the respective examples of FIGS. 6A and 6B). As a non-limiting example, the first masking height (or masking depth) may be 25% and the second masking height (or masking depth) may be 50%. As a result, the first and second spark stand plates may be used interchangeably such that, for example, one of the first and second spark stand plates providing a masking height (or masking depth) more suitable for the measurement under consideration is selected. Considering the above example with different properties of iron matrix sample and aluminum matrix sample, a first spark stand plate providing a masking height (or masking depth) of 25% may be applied for the measurement of the iron matrix sample, while a second spark stand plate providing a masking height (or masking depth) of 50% may be applied for the measurement of the aluminum matrix sample. In a variation of this example, the two or more spark stand plates may comprise three or more spark stand plates, each of which comprises a spatial mask having a masking height (or masking depth) different from the respective masking height (or masking depth) of the others of the three or more spark stand plates.

[0045] As a further example of providing the spark stand plate 130 with a spatial mask, Fig. 6E shows an example that shows, in schematic form, a spark stand plate 130 with a masking member 133b attached to an inner surface of the spark stand plate 130 in a portion that spatially coincides with the notch 125 of the spark stand plate 130 when the spark stand plate 130 is fixed in its position on the spark stand body 121. As a result, when the spark stand plate 130 is placed on the upper surface of the spark stand body 121, the masking member 133b extending from the inner surface of the spark stand plate 130 can protrude into the notch 125 located on the upper surface of the spark stand body 121, thereby acting as a spatial mask that partially blocks the view (from the opening through the mounting flange 122) of the conical plasma 132. FIG. 6F illustrates diagrammatically a spatial mask provided as a masking member 133b according to another example, where the masking member 133b provides a higher masking height (or masking depth) compared to that of the example of FIG. 6E.

[0046] In one example, the masking member 133b may be removably attached to the inner surface of the spark stand plate 130. As a result, the spark stand plate 130 may be applied with or without the masking member 133b acting as a spatial mask according to the measurement under consideration. In a variation of this example, the spark stand assembly 120 may comprise two or more masking members 133b (e.g., according to the respective examples of FIGS. 6E and 6F), each providing a masking height (or masking depth) different from the masking height (or masking depth) of the other one of the two or more masking members, thereby providing the user with the choice of using the spark stand plate without the masking member 133b or using one of the two or more masking members 133b having the masking height (or masking depth) that is considered most appropriate for the measurement under consideration.

[0047] In the example illustrated through Figures 6A-6F, the spatial mask is provided at least or immediately adjacent to the rim of the aperture 131 through the spark stand plate 130. This is advantageous in that it allows for additional freedom in selecting the placement of the entrance slit relative to the central axis of the conical plasma 132, where the entrance slit may be applied as an entrance aperture to the optical splitter 114a. The spatial mask located at or immediately adjacent to the rim of the aperture 131 ensures that the desired spatial mask is provided regardless of the placement of the entrance slit, including scenarios where the entrance slit is parallel or substantially parallel to the central axis of the conical plasma 132. In other examples, the spatial mask can be provided at a position further away from the rim of the aperture, essentially anywhere along the notch 125 between the recess and the mounting flange 122, while such placement of the spatial mask can ensure the desired spatial masking in scenarios where the entrance slit is perpendicular or substantially perpendicular to the central axis of the conical plasma 132, while providing at least partially tailored masking performance for other entrance slit placements.

[0048] The aforementioned embodiment includes a seal member groove 126 disposed on the upper surface of the spark stand body 121 to facilitate disposing the seal ring 127 between the upper surface of the spark stand body 121 and the spark stand plate 130, such that the seal ring 127 surrounds the recess and elongated notch 125 disposed on the upper surface and is disposed over the raised portion 124 disposed on the upper surface. In other examples, the seal member groove 126 may be omitted from the upper surface of the spark stand body 121, but the seal member groove 126 may instead be disposed on the inner surface of the spark stand plate 130. In such an approach, the seal member groove 126 may be disposed on the inner surface of the spark stand plate 130, such that the seal member 127 surrounds the recess at least partially recessed therein and the elongated notch 125 disposed on the upper surface of the spark stand body 121 and is disposed over the raised portion 124 when the spark stand plate 130 is disposed in its position on the upper surface of the spark stand body 121.

[0049] The above-described embodiments assume that the spark stand assembly 120 is removably attached to the main housing 110 of the OES apparatus 100 via a removably attached mounting flange 122 to a mounting interface provided on the main housing 110. In other examples, the spark stand assembly 120 may be mounted to the main housing 110 in a fixed manner such that correct spatial alignment between the second transmission path of the spark stand assembly 120 and the first transmission path of the main housing 110 is provided. In such a scenario, the spark stand assembly 120 may be attached to the mounting interface of the main housing 110 via the mounting flange 122 as part of the manufacturing, installation, or configuration process of the OES apparatus 100, but may not provide for subsequent removal of the spark stand assembly 120 by a user. Further, alternatively or additionally, the mounting of the spark stand assembly 120 to the main housing 110 of the OES device 100 may differ from that illustrated in the schematic diagram of Figure 1, such as, for example, the spark stand assembly 120 being mounted on top of the main housing 110. In further embodiments, the spark stand assembly 120 may be at least partially embedded and / or integrated into the main housing 110 of the OES device 100.

[0050] While the examples provided thus far describe certain aspects of the structure and properties of the spark stand assembly 120 according to the present disclosure, other descriptions are not directly relevant for brevity and clarity of description of many aspects of the structure and / or operation that may be commonly applied to spark stands, as applied in the context of OES devices known in the art, to describe advantageous aspects of the spark stand assembly 120. Examples of such embodiments include a gas inlet and outlet(s) to the plasma chamber and / or outlet(s) from the notch 125 that may be provided to allow for the transfer of inert gas to the plasma chamber and / or to generate a UV-transparent atmosphere in the plasma chamber and / or a notch 125 for performing measurements, and / or for purging the plasma chamber and / or notch 125 between measurements, and / or for purging a portion of the sample 140 exposed through the opening 131 through the spark stand plate 130 when performing measurements. In this regard, the spark stand body 121 may include one or more gas inlets for injecting an inert gas (such as argon) into the plasma chamber for purging, and one or more outlets for removing the inert gas and any debris formed during plasma generation from the plasma chamber. Additionally, the spark stand assembly 120 may further include respective configurations for injecting an inert gas into the plasma chamber and / or the notch 125 via the one or more gas inlets, and receiving the inert gas and debris from the plasma chamber and / or the notch 125 via one or more outlets.

[0051] Although the foregoing examples describe the structure and characteristics of OES apparatus 100 with at least implicit reference to spark OES analysis, the examples provided in this disclosure are readily generalized for application to analytical apparatus using different OES techniques, such as arc OES or laser-induced breakdown spectroscopy (LIBS).

Claims

1. A spark stand assembly (120) for an emission spectrometer (OES) apparatus (100), wherein the spark stand assembly (120) is A spark stand body (121) is attached to a mounting flange (122) that enables the spark stand assembly (120) to be attached to the main housing (110) of the OES device (100), Excitators (123, 123a) are arranged in recesses on the upper surface of the spark stand body (121), A raised portion (124) is positioned on the upper surface of the spark stand body (121) adjacent to the mounting flange (122), The spark stand body (121) has an elongated notch (125) positioned on its upper surface, which connects the recess to a path passing through the raised portion (124), A spark stand plate (130) is detachably attached to the upper surface of the spark stand body (121) so as to cover the recess, the notch (125), and at least a portion of the raised portion (124), wherein the recess forms a part of the optical transmission path from the plasma chamber to the path, and the spark stand plate (130) includes an opening (131) for exposing a portion of a sample (140) placed in the opening (131) for excitation from the exciters (123, 123a), and the opening (131) is positioned so as to be spatially aligned with the exciters (123, 123a) when the spark stand plate (130) is attached to the upper surface of the spark stand body (121), A sealing member (127) is positioned between the upper surface of the spark stand body (121) and the spark stand plate (130) so as to surround the recess and the notch (125), and is routed beyond the raised portion (124), A spark stand assembly (120) comprising the following.

2. The spark stand assembly (120) according to claim 1, comprising a seal member groove (126) positioned on the upper surface and the raised portion (124) of the spark stand body (121) so as to surround the recess and the notch (125), wherein the seal member (127) is at least partially embedded in the seal member groove (126).

3. The spark stand assembly (120) according to claim 1, comprising a seal member groove (126) disposed on the opposing surface of the spark stand plate (130) facing the spark stand body (121), wherein the seal member (127) is at least partially embedded in the seal member groove (126), and the seal member groove (126) is arranged such that when the spark stand plate (130) is attached to the upper surface of the spark stand body (121), the seal member (127) surrounds the recess and the notch (125) and is routed beyond the raised portion (124).

4. The spark stand assembly (120) according to any one of claims 1 to 3, wherein the spark stand plate (130) can be attached to the upper surface of the spark stand body (121) by pressing the spark stand plate (130) against the upper surface of the spark stand body (121).

5. The spark stand assembly (120) according to claim 4, comprising a mounting mechanism positioned to press the spark stand plate (130) against the upper surface of the spark stand body (121).

6. The spark stand assembly (120) according to claim 5, wherein the mounting mechanism comprises a set of clamps for pressing the spark stand plate (130) against the upper surface of the spark stand body (121).

7. The spark stand assembly (120) according to any one of claims 1 to 3, wherein the opposing surface of the spark stand plate (130) facing the spark stand body (121) is separated from the recess and the notch (125) and has a shape substantially corresponding to the shape of the upper surface of the spark stand body (121).

8. The spark stand assembly (120) according to claim 7, wherein the upper surface of the spark stand body (121) is substantially flat away from the recess, the notch (125) and the raised portion (124), and the opposing surface of the spark stand plate (130) facing the spark stand body (121) is substantially flat away from the portion intended to abut against the raised portion (124).

9. The spark stand assembly (120) according to any one of claims 1 to 3, wherein the optical transmission path comprises a coupling lens or window for isolating at least a portion of the optical transmission path from the plasma chamber.

10. The spark stand assembly (120) according to any one of claims 1 to 3, wherein the exciter (123) comprises an electrode (123a) positioned to generate spark excitation that converts a portion of the sample (140) into a plasma state, thereby generating a conical plasma (132) between the tip of the electrode (123a) and the surface of the sample (140) when the electrode (123a) is activated.

11. The spark stand assembly (120) according to any one of claims 1 to 3, wherein the spark stand plate (130) includes a space mask (133a, 133b) that protrudes from the surface of the spark stand plate (130) facing the spark stand body (121) and is positioned to be spatially aligned with the notch (125) when the spark stand plate (130) is attached to the upper surface of the spark stand body (121), thereby partially blocking the optical transmission path from the plasma chamber to the path.

12. The spark stand assembly (120) according to claim 11, wherein the spatial mask (133a, 133b) includes a masking portion (133a) provided as a thickened portion of the spark stand plate (130) that protrudes into the notch (125) when the spark stand plate (130) is attached to the upper surface of the spark stand body (121).

13. The spark stand assembly (120) according to claim 11, wherein the spatial mask (133a, 133b) comprises a masking member (133b) detachably attached to the spark stand plate (130), and when the spark stand plate (130) is attached to the upper surface of the spark stand body (121), the masking member (133b) protrudes into the notch (125).

14. The spark stand assembly (120) according to claim 11, wherein the height of the space mask (133a, 133b), measured from the outer surface of the spark stand plate (130), is 25 to 70% of the distance between the tip of the exciter (123, 123a) and the outer surface of the spark stand plate (130).

15. An emission spectrometer (OES) apparatus (100) comprising a main housing (110) and a spark stand assembly (120) according to any one of claims 1 to 3, wherein the main housing (110) comprises a photospectroscopic detection assembly (114) and a mounting interface for mounting the spark stand assembly (120) to the main housing (110), the mounting interface comprising an optical interface for connecting the optical transmission path of the spark stand assembly (120) to the photospectroscopic detection assembly (114).

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