Calibration and testing of optical particulate sensors

Abstract

To provide a system, of which size, weight, and complexity are reduced, for calibration and testing an optical particulate sensor.SOLUTION: A system 100 for calibration and testing an optical particulate sensor includes: a carrier 116 having a micro target 113 configured to emulate a particle; a frame 118 configured to position the micro target to pass through a measurement volume 108 of the optical particulate sensor; a vibration drive section 120 coupled to the frame and configured to move the frame such that the micro target on the carrier moves through three dimensions of the measurement volume, such that a light beam from the optical particulate sensor is reflected / scattered toward the optical particulate sensor; and a processor 128 configured to determine characteristics of the micro target on the carrier on the reflected / scattered light.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] (Statement regarding federally sponsored research and development) This invention was made with government support under S0176492 / 101102008 awarded by CAJU. The government has certain rights in this invention.

[0002] (CROSS-REFERENCE TO RELATED APPLICATIONS) This U.S. non-provisional patent application claims the benefit of earlier-filed U.S. Provisional Patent Application No. 63 / 568,685, filed March 22, 2024 (the '685 application), and earlier-filed U.S. Provisional Patent Application No. 63 / 737,998, filed December 23, 2024 (the '998 application). The '685 application and the '998 application are incorporated herein by reference. [Background technology]

[0003] Optical particle sensors are implemented in many types of systems, such as aircraft, for atmospheric condition sensing. Such sensors can be implemented as lidar systems that use optical signals to analyze the characteristics of small and large particulate matter (water droplets, ice crystals, volcanic ash, sand, and aerosol particles such as dust particles) in the aircraft's surrounding environment. Optical particle sensors are periodically calibrated and tested to ensure consistent function and optimal performance.

[0004] Existing systems and methods for testing and calibrating such optical particle sensors are large, heavy, and complex. Furthermore, such systems are typically limited to use in laboratory environments due to the use of pressurized air used for aerosolizing the distilled water supply or solid particle size standards to generate the test droplets. Furthermore, such equipment requires regular maintenance and cleaning to function properly.

[0005] Therefore, a need exists to reduce the size, weight, and complexity of systems used to test optical particle sensors. Summary of the Invention

[0006] Details of one or more embodiments are set forth in the description below. Features illustrated or described in connection with one exemplary embodiment may be combined with features of other embodiments. Accordingly, any of the various embodiments described herein can be combined to provide further embodiments. Aspects of the embodiments can be modified, as necessary, to employ concepts from any patents, applications, and publications identified herein to provide still further embodiments.

[0007] In one embodiment, a system for calibrating and testing an optical particle sensor is provided, the system including: a carrier having at least one micro target configured to emulate a particle; a frame configured to receive the carrier, the frame further configured to position the at least one micro target to pass through a measurement volume of the optical particle sensor; a drive coupled to the frame configured to move the frame such that the at least one micro target on the carrier moves through three dimensions of the measurement volume such that a light beam from the optical particle sensor is reflected / scattered toward the optical particle sensor; and at least one processor configured to determine one or more characteristics of the at least one micro target on the carrier based on the reflected / scattered light. [Brief explanation of the drawings]

[0008] Example embodiments are described with additional specificity and detail through the use of the accompanying drawings, as described below and in conjunction with the detailed description, with the understanding that the drawings depict example embodiments only and therefore should not be considered limiting in scope. [Figure 1A] FIG. 1 shows a block diagram of one embodiment of a system for testing optical particle sensors. [Figure 1B]1B is a schematic diagram of a portion of the system of FIG. 1A showing two aspects of the sensor sampling range and the sensor measurement volume. [Figure 2] 10 illustrates airflow and calibration target movement according to one embodiment of a laser beam profile. [Figure 3A] 2 is a perspective view of one embodiment of a frame for holding a carrier with multiple micro targets for the system of FIG. 1. FIG. [Figure 3B] 2 is a perspective view of one embodiment of a frame for holding a carrier with multiple micro targets for the system of FIG. 1. FIG. [Figure 4] 2 is a table containing data showing the output by the system of FIG. 1 for micro-targets of various sizes. [Figure 5] 5 is a graph showing a calibration curve based on the data from FIG. 4. [Figure 6] 2 is a table containing data mapping the measurement volume of the system of FIG. 1. [Figure 7A] 7 is a graph showing optical responses from a uniformity test for various positions of a calibration micro-target within the measurement volume of an optical particle sensor, based on the data of FIG. 6; [Figure 7B] 10 is a graph showing the optical response of a calibration microtarget within the sensor measurement volume as well as the optical response of a calibration microtarget outside the sensor measurement volume. [Figure 8] 2 is a side view of one embodiment of a carrier with multiple micro-targets illustrating possible error sources in a system for testing the optical particle sensor of FIG. 1. [Figure 9] 9 is a side view of another embodiment of a carrier having a plurality of micro targets with triangular cross sections that reduces potential errors in the carrier and micro targets of FIG. 8. [Figure 10] 2 is a side view of another embodiment of a carrier and microtarget for use in the system of FIG. 1. [Figure 11] FIG. 11 is a front view of one embodiment of the carrier and microtarget of FIG. 10. [Figure 12]1 is a flow chart of one embodiment of a process for testing an optical particle sensor. [Figure 13] FIG. 1 is a block diagram of one embodiment of a system for testing and calibrating an optical particle sensor having targets on a rotating wafer or disk. [Figure 14] 14 is a graph illustrating an exemplary relationship between linear velocity and radius of the rotating wafer or disk of FIG. 13. [Figure 15A] FIG. 1 is a perspective view of one embodiment of a carrier having a cone-shaped target formed thereon. [Figure 15B] FIG. 1 is a perspective view of one embodiment of a carrier having a cone-shaped target formed thereon. [Figure 15C] FIG. 1 is a perspective view of one embodiment of a carrier having a cone-shaped target formed thereon. [Figure 15D] FIG. 1 is a perspective view of one embodiment of a carrier having a cone-shaped target formed thereon. [Figure 15E] FIG. 1 is a perspective view of one embodiment of a carrier having a cone-shaped target formed thereon. [Figure 16A] FIG. 10 is a perspective view of another embodiment of a carrier formed from concentric cylinders of decreasing width forming a stack with a target formed on the surface of each cylinder. [Figure 16B] FIG. 10 is a perspective view of another embodiment of a carrier formed from concentric cylinders of decreasing width forming a stack with a target formed on the surface of each cylinder. [Figure 16C] FIG. 10 is a perspective view of another embodiment of a carrier formed from concentric cylinders of decreasing width forming a stack with a target formed on the surface of each cylinder. [Figure 17A] FIG. 10 is a perspective view of another embodiment of a disk or wafer shaped carrier having four portions or sections with targets formed thereon. [Figure 17B] FIG. 17B is a top view of one embodiment of the carrier of FIG. 17A. [Figure 18]FIG. 17B is a top view of an alternative embodiment of the carrier of FIG. 17A having eight portions or sections.

[0009] According to common practice, the various illustrated features are not drawn to scale but rather to emphasize specific features relevant to the exemplary embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific illustrative embodiments. It should be understood, however, that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the methods presented in the drawings and specification should not be construed as limiting the order in which individual steps may be performed. Accordingly, the following detailed description is not to be construed in a limiting sense.

[0011] Optical particle sensors (OPSs) use a laser or other light source and a photodetector to collect data about particles within the sensor's measurement volume. Essentially, the OPS illuminates particles within its measurement volume, and the photodetector collects data from the light signal reflected / scattered by the particles. To test an OPS, particles, typically microdroplets of water of known size and composition, are introduced into the OPS's measurement volume using an elaborate laboratory setup.

[0012] Embodiments of the present invention replace conventional water droplet or particle standards and their associated equipment with dedicated calibration devices in which solid micro-targets are positioned on a carrier, e.g., an optically transparent material, or integrated into a carrier to test and / or calibrate optical particle sensors. Various embodiments of micro-targets that can be used to test and calibrate OPSs are described in detail below. Avoiding the need to generate water droplets or aerosolize particle standards allows for high repeatability, high calibration accuracy, and significantly reduces the size, weight, complexity, and cost of the calibration device.

[0013] Microtargets used in embodiments of the present invention are formed from any suitable material to produce lines, dots, two-dimensional, or three-dimensional particle structures of appropriate size (e.g., width and / or diameter) and reflectivity. The microtargets are designed to simulate or emulate potential particles that may be sensed by the OPS under test. Therefore, the dots and lines are sized similarly to those potential particles. In addition, because particles reflect / scatter light from the OPS, the material, such as metal, from which the microtarget is formed similarly reflects / scatters light from the OPS. This allows the OPS to receive light reflected / scattered by the microtarget, such that the detector of the OPS can generate an output that correlates to a characteristic (e.g., size) of the particle being sensed by the OPS under test.

[0014] Oscillating Carrier 1A is a block diagram of one embodiment of a system 100 for testing and calibrating an optical particle sensor (OPS) 102. The OPS 102 includes transmission optics (e.g., laser 104) and a detector 106. The laser 104 of the OPS 102 illuminates a measurement volume 108 with light. Particles within the measurement volume 108 reflect / scatter the light from the laser 104 toward the OPS 102. This reflected / scattered light passes through receiving optics (e.g., lens 110) and enters the detector 106, which includes a photodetector that measures the amount of light reflected by any particles present within the measurement volume 108. The detector 106 generates an output signal based on the photodetector response that is provided to the system 100.

[0015] Instead of generating and injecting particles into the measurement volume 108 of the OPS 102, the system 100 places a micro-target 113 in the measurement volume 108 of the OPS 102 to simulate the presence of particles moving through the measurement volume 108. In one embodiment, the micro-target 113 includes dots 112 and lines 114 on a carrier 116. In one embodiment, the carrier 116 and the micro-target 113 are Edmund Optics Micro Line & Dot Swatch Micrometers. The Edmund micrometers include precision line and dot targets ranging in size from 2 to 100 micrometers (microns) that are fabricated by depositing chrome on glass or chrome on opal. It is understood that the Edmund micrometer is provided by way of example and not limitation.

[0016] The carrier 116 is mounted on a frame 118 so that a selected one of the microtargets 113 (dots 112 and lines 114) is positioned within the measurement volume 108. Each microtarget 113 on the carrier 116 is usable for testing the OPS 102. During testing, the selected microtarget 113 is moved up and down through the measurement volume 108 along an axis of oscillatory motion 119 by an oscillatory drive 120 to simulate particle motion within the measurement volume 108. To simulate particle motion, the selected microtarget 113 leaves the measurement volume 108 at each end of the oscillation before its direction of motion changes with a maximum shift (amplitude) of the oscillation. In one embodiment, the photodetector of the detector 106 cannot detect the direction of flight of the microtarget 113 (or a particle in normal operation). Therefore, oscillating the microtarget during testing in the same direction as the expected movement of the particle during normal operation produces the same net result in the output of the detector 106. That is, the number of microtargets 113 detected by OPS 102 is twice the vibration frequency of vibration drive 120 (e.g., 100 "particles" are detected for a 50 Hz vibration frequency of vibration drive 120). In addition, system 100 also includes a target positioner 122 that is used to adjust the position of carrier 116 and its microtargets 113 (dots 112 and lines 114) within measurement volume 108 of OPS 102 and to select the microtarget 113 to be used for testing when several microtargets 113 are available on carrier 116.

[0017] In some embodiments, system 100 includes a light conditioning subsystem 130 that conditions or modifies the incident light from laser 104 (laser beam 124). In one embodiment, light conditioning subsystem 130 is an attenuator that attenuates the light from laser 104 to prevent overloading the photodetector of detector 106. In other embodiments, light conditioning subsystem 130 provides a half-wave plate configured to rotate the polarization of the light from laser 104 by 90 degrees so that sensors that use polarized light can be tested by system 100. In other embodiments, light conditioning subsystem 130 modifies any suitable characteristics of the light from laser 104 to enable system 100 to test / calibrate all sensor channels.

[0018] In one embodiment, system 100 is implemented in a simple, rugged, and compact test / calibration device with low power requirements. In another embodiment, system 100 is a benchtop test / calibration device that can be attached to OPS 102 and used in production or at a factory prior to installing sensors, for example, on an aircraft. In yet another embodiment, system 100 is a portable, battery-powered device that includes an interface configured or adapted to be attached, for example, to a sensor window on the aircraft surface and used to test OPS 102 without removing it from the aircraft. When used to test sensors installed on an aircraft, the sensor under test may be covered by an additional window that protects the sensor and ensures the aerodynamics of the aircraft body, with the transparency of the additional window also being tested.

[0019] During operation, particles of a particular size are simulated within the measurement volume 108 by using a target positioner 122 to position an appropriate microtarget 113 (dot 112 or line 114) on the carrier 116 in a position such that a vibration driver 120 can move the dot 112 or line 114 up and down throughout the measurement volume 108 to simulate particle movement. The laser 104 of the OPS 102 transmits incident light (laser beam 124) through the measurement volume 108. When a selected dot 112 or line 114 passes through the incident light, reflected / scattered light 126 passes through the lens 110 into the detector 106, and data is sent to the processing system 128. Embodiments of the OPS 102 include an interface for communicating with the processing system 128 of the system 100 via either wireless communication or a dedicated wired connection, enabling automatic sensor calibration. Note that microtargets with symmetrical shapes, such as dots, are better suited to emulating the behavior of aerosol particles. This is particularly useful for three-dimensional mapping of the measurement volume 108 of the OPS 102, where precise positioning of the microtarget 113 improves the accuracy of mapping the measurement volume 108. Microtargets with highly asymmetric shapes, such as lines, are more suitable for determining the average optical response within one dimension of the measurement volume 108. Because the length of the line microtarget is larger than the measurement volume 108 of the OPS 102, it is less sensitive to the positioning setup.

[0020] 1B is a schematic diagram of a portion of system 100 of FIG. 1A showing two aspects of system 100: a sensor sampling range 140 of OPS 102 and a sensor measurement volume 108. Detector 106 of OPS 102 is designed to measure particles only from a specific sensor sampling range 140 from the surface of the receiving optics (lens 110). Measurement volume 108 is the intersection of sensor sampling range 140 and laser beam 124 from laser 104. When an aerosol particle passes through laser beam 124 and exits measurement volume 108, the reflected / scattered light received by the receiving optics (lens 110) does not reach the sensor photodetector of detector 106 because the received optical signal is blocked by the sensor slit.

[0021] In one embodiment, when the laser beam profile is observed from the measurement volume 108 in the direction of the laser 104, the laser beam bundle 208 has a profile as shown in FIG. 2. The horizontal bundle has a flat-top window profile 205, and the vertical bundle has a Gaussian profile 207. The airflow direction 220 is approximately from the top of the image to the bottom of the image. The vibration driver 120 moves the microtarget 113 on the same axis as the airflow direction 220, as marked by the target set movement direction arrow 222. The flat-top window profile 205 is approximately perpendicular to the airflow direction 220; therefore, aerosol particles passing through the measurement volume 108 following different trajectories, such as left 210, center 212, or right 214, travel through the same laser beam bundle and therefore generate an optical response independent of trajectory position. The sensor measurement window width 202 defined by the receiving optics including the slit is smaller than the laser beam flat-top window width 204 to avoid optical response measurements due to undefined illumination flux present at the edge of the flat-top window profile 205.

[0022] Although objects sensed by OPS 102 have size ranges in the micrometer range, measurement volume 108 is in the millimeter range, and sensor sampling distances are in the centimeter / decimeter range, all optical components of laser 104 and receiving optics (including lens 110) must be precisely aligned with their optical axes lying in a single plane. Calibration and functional testing of OPS 102 consists of identifying the location and size of measurement volume 108 and verifying the optical response uniformity within measurement volume 108. Misalignment of the transmit and receive optics is detected as performance degradation in specific regions of measurement volume 108. System 100 can provide target sizes and orbital locations with the repeatability required to generate calibration data for OPS 102.

[0023] The system 100 also verifies the sensor's ability to reject measurements from the measurement volume 108. A microtarget 113 is moved through the laser beam 124 outside the sensor sampling range 140, and therefore outside the measurement volume 108. If the laser 104 and receiving optics (including the lens 110) are properly aligned, an optical response should be blocked by the receiving optics slit and no aerosol particles should be detected. If an optical response is detected by the detector 106, it indicates a potential risk of misalignment of the sensor optics, and a maintenance flag is raised.

[0024] To fully verify the proper functioning of the OPS 102, the microtarget 113 is moved in all three spatial dimensions and verification of the proper optical response is generated throughout the measurement volume 108, verifying the ability of the OPS 102 to reject the optical response generated by the microtarget 113 from the measurement volume 108.

[0025] As described in more detail below, a processing system 128 processes the digitized light flash 126 from the output of the detector 106 and calculates the characteristics of the microtarget, such as its size. By comparing the calculated characteristics to known characteristics of the microtarget, calibration factors can be calculated and used in the OPS 102 during normal operation, with corrections based on material differences (microtarget vs. expected particles), to ensure optimal performance and consistent functioning of the OPS 102.

[0026] FIG. 3A is a perspective view of one embodiment of a frame 300 used as frame 118 of FIG. 1A to position a set of microtargets for the system of FIG. 1A. FIG. 3B further shows frame 300 mounted on a membrane-based vibration drive 302, which is one embodiment of vibration drive 120 of FIG. 1A. Vibration drive 302 can generate sufficient amplitude to move the microtargets in the direction of arrow 310 throughout the measurement volume of the OPS under test. Note that the vibration amplitude and frequency can be adjusted to meet the characteristics of a particular OPS, such as the dimensions of the measurement volume or the maximum allowable duration of a single particle response. For example, in one embodiment, the vibration amplitude is approximately 2 millimeters (mm), allowing the microtargets to pass through the entire measurement volume of a sensor having a measurement volume of approximately 1 mm. In one embodiment, the vibration frequency is selected to be approximately 50 Hz because this frequency provides stability for the movement of the microtargets within the assembled test system prototype. Other frequencies and amplitudes can be selected based on the sensor under test. It is also possible to move the micro-target in discrete steps and measure the micro-target optical response while the micro-target is stationary.

[0027] As shown in FIG. 3A , frame 300 is fabricated in the form of a rectangle with a central opening 304 and a groove for receiving carrier 306 with microtarget 308 formed inside. Carrier 306 and microtarget 308 correspond to carrier 116 and microtarget 113 in FIG. 1A . In this embodiment, frame 300 is tilted at an angle from front to back to correspond to the orientation of the incident light emanating from the OPS being tested. Specifically, the tilt angle is selected so that the incident light from laser 104 (laser beam 124) is reflected directly onto detector 106 along optical axis 121 of detector 106. In other embodiments, the frame has other orientations that allow the microtarget to oscillate throughout the measurement volume of the particular OPS being tested; for example, there is no tilt so that microtarget 113 oscillates along the same path as an actual particle in an actual measurement. In other embodiments, the tilt angle for frame 300 can be adjusted based on the OPS being tested.

[0028] FIG. 4 shows a table 400 containing data output by the system 100 of FIG. 1A for line microtargets 113 of various sizes oscillating through the center of the measurement volume 108 of the OPS 102. In the data set of table 400, row 402 indicates the size (in microns) of the microtarget 113 tested to generate each column of data. Row 404 includes a graph 406 of that column's microtarget size, showing a curve 408 generated by the output of the detector 106 of the OPS 102. The peak size of the curve 408 is shown along with the signal duration. This data is correlated in row 410 of table 400 with the size of the "particles" detected by the OPS 102 and processed by the processing system 128. When the microtargets 113 are oscillated through the measurement volume 108 at a frequency of 50 Hz, the OPS 102 detects 100 particles because the "particles" pass through the measurement volume twice during each oscillation. Row 410 includes a chart 412 showing the number of particles of each size detected by OPS 102 in each column. In the 9-micron micro-target column, chart 412 shows fewer than 100 particles of 8 microns, along with a small number of particles of other sizes. The deviation from 100 particles detected by OPS 102 is explained by false positive and false negative detections. Note that these other particles represent noise that may be due to imperfections in the surface of carrier 116, which cause extraneous input from reflections from the surface of carrier 116 to detector 106. Note that in the 50-micron micro-target column, the amplitude of the optical response was very close to the boundary between 13-micron and 14-micron water droplets. Thus, approximately 50% of the particles were marked as 13 microns, and another approximately 50% of the particles were marked as 14 microns. Furthermore, note that OPS 102 detected particle sizes that differed from the actual size of the micro-targets. This is due to differences in reflectivity and other properties of the micro-targets compared to the particles detected by OPS 102. When these material differences are accounted for, data from OPS 102 (calculated properties, e.g., size) can be used along with known properties to calculate calibration factors, allowing OPS 102 to accurately detect particle properties during operation.

[0029] FIG. 5 is a graph 500 showing a calibration curve 502 based on the data from FIG.

[0030] FIG. 6 shows a table 600 containing data mapping the measurement volume 108 of the system of FIG. 1. The measurement volume of the OPS 102 is tested using a dot microtarget to verify the uniformity of the OPS 102 sensor response across the measurement volume 108. Measurements begin at a location outside the sensor sampling range 142, and the microtarget 113 is moved through the laser beam 124. A background optical response is measured. The microtarget 113 is then moved into the sensor sampling range 140, and an optical response in the form of peaks 611 and 612 is measured as the microtarget 113 moves through the laser beam 124. Finally, the microtarget 113 is moved out of the sensor sampling range 140, and the background optical response is again measured. Two peaks 611 and 612 are detected as the microtarget 113 crosses the laser beam 124 twice per oscillation period. When the dependence of peak amplitude on target carrier position is plotted, the test produces a cross section of measurement volume 108 (curve 702 of graph 700 in FIG. 7A ). In curve 702, top 704 is substantially flat and edges 706 are substantially steep across measurement volume 108.

[0031] To generate curve 702, measurements are taken with the OPS 102 while the microtarget 113 is moved through multiple horizontal positions (distances) from the OPS 102. Example test results at various distances are shown in table 600. In row 602, the distance (horizontal position) from the OPS 102 to the target is recorded. Because the optical response occurs only when the microtarget 113 intersects the laser beam 124, the target vertical position needs to be adjusted slightly during the measurement. In row 604, a graph 606 is included for the distance associated in row 602 for that column. Graph 606 includes a curve 608 showing the readings from the sensor for the target at that distance. Note that the uneven shape of the base of curve 608 is due to imperfections in the version of the carrier for the microtarget used in this test. Generally, sensors treat low-frequency signals as bias, which can be caused by, for example, solar background; therefore, only peaks 611, 612 with transition times below a minimum specified threshold are considered to be aerosol particles. The signal amplitude is recorded in row 610 and captured in curve 702 of graph 700. Note that curve 702 has a substantially flat central portion at about 350 mV between about 17.85 mm and 18.71 mm.

[0032] To map the measurement volume 108 of the OPS 102 in three dimensions, the measurements described above are performed on a microtarget 113 having multiple depth positions. The depth positions represent the microtarget positions within the laser beam flat-top window width 204. The depth axis is perpendicular to the plane defined by the light receiving axis 121 and the vibration motion axis 119, meaning that the microtarget is moved toward or away from the computer screen or paper. Such measurements are performed and the results are displayed in the wireframe 3D surface graph shown in FIG. 7B. The graph in FIG. 7B verifies the horizontal size of the measurement volume 108, which in this example is approximately 1.0 mm. In addition, the graph in FIG. 7B also verifies the depth size of the measurement volume 108, which in this example is approximately 0.4 mm. The third dimension of the measurement volume is given by the movement of the microtarget 113 through the laser beam Gaussian profile 207. To test the laser beam Gaussian profile, a micro-target 113 can be used that has a size significantly smaller than the laser beam Gaussian width, and therefore its optical response will be proportional to the laser beam flux density. Such measurements can be seen as peaks 611, 612 in curve 608 in Figure 6.

[0033] 8 is a side view of one embodiment of a carrier 800 having a plurality of microtargets 802 formed on a surface of the carrier 800. This embodiment of the carrier 800 includes microtargets 802 formed of a reflective material, such as metal, spaced apart on the surface of the carrier 800. Surfaces 804 of the microtargets 802 are substantially flat and parallel to a surface 806 of the carrier 800. The size of the microtargets 802 can be varied to represent particles of different sizes and enable OPS calibration using a single carrier 800. The distance between the microtargets 802 is selected so that only one microtarget 802 enters the measurement volume 108 of the OPS 102 at a time.

[0034] FIG. 8 illustrates a possible source of error for a system for testing optical particle sensors, such as system 100 of FIG. 1. As shown, the OPS under test illuminates a carrier 800 and a microtarget 802 with incident light 808. The incident light 808 is reflected by both the surface 804 of the microtarget 802 (reflected light 810) and the surface 806 of the carrier 800 (reflected light 812). A detector of the OPS under test receives both the reflected light 810 from the surface 804 of the microtarget 802 and the reflected light 812 from the surface 806 of the carrier 800. Unfortunately, the inclusion of light 812 from the surface 806 of the carrier 800 introduces error into the output of the OPS under test.

[0035] FIG. 9 is a side view of another embodiment of a carrier 900 having a plurality of microtargets 902 formed on the surface of the carrier 900. This embodiment of the carrier 900 includes microtargets 902 formed of a reflective material, such as metal, spaced apart on the surface of the carrier 900. The surface 904 of the microtarget 902 is formed at an angle relative to the surface 906 of the carrier 900 so that the microtarget 902 has a triangular cross-section, which reduces potential errors in the microtarget 902 of FIG. 8. In this embodiment, incident light 908 reflecting from the surface 906 of the carrier 900 is reflected away from the detector of the OPS under test, as shown by reflected light 912, while incident light 908 reflecting from the surface 904 of the microtarget 902 enters the detector of the OPS under test, as shown by reflected light 910. Therefore, by tilting the surface 904 of the microtarget 902 relative to the surface 906 of the carrier 900, the detector does not receive light reflecting from the surface 906 of the carrier 900. This eliminates a source of error for the detector of the OPS under test.

[0036] FIG. 10 is a side view of another embodiment of a carrier 1000 having multiple microtargets 1002 for use in the system of FIG. 1. FIG. 11 is a front view of one embodiment of the target of FIG. 10. In this embodiment, unwanted reflections from the carrier 1000 are reduced by forming the microtarget 1002 by elongating a calibrated metal wire or bar of cross section with a flat surface directed toward the incident light across an opening 1004 in the carrier 1000, so that light not reflected from the microtarget 1002 passes through the carrier 1000. As shown in FIG. 10, incident light 1008 from the OPS under test is directed toward a portion of the carrier 1000. A portion of the incident light 1008 is reflected toward a detector of the OPS under test, as shown by reflected light 1010 from a surface 1006 of the microtarget 1002 used for testing. However, aperture 1004 allows incident light 1008 near selected microtarget 1002 to pass through aperture 1004 in carrier 1000 and not be inadvertently reflected into a detector of the OPS under test, thereby improving the operation of the system of FIG. 1 for testing or calibrating the OPS under test.

[0037] In this embodiment, the surface 1006 of the microtarget 1002 may also be inclined relative to the surface 1014 of the carrier 1000 .

[0038] 12 is a flow chart of one embodiment of a process 1200 for testing an optical particle sensor (OPS). In one embodiment, process 1200 tests the OPS using system 100 of FIG. 1. However, process 1200 is not limited to use with system 100 and can be implemented with any suitable system that uses micro-targets to simulate particles within the working volume of the OPS.

[0039] Process 1200 includes, in block 1201, inserting a carrier on which a set of microtargets is formed into a frame. Additionally, in block 1203, process 1200 positions at least one microtarget on the carrier so that it passes through a measurement volume of an optical particle sensor. This positioning may, in some embodiments, include selecting one of the set of microtargets for detection by the OPS. To detect the microtarget, process 1200 drives the frame to oscillate the carrier, moving the selected microtarget throughout the measurement volume of the OPS, in block 1205. Note that the oscillation amplitude must be large enough to allow the microtarget to leave the measurement volume at both ends of the oscillation. Furthermore, in block 1207, process 1200 receives light reflected / scattered by the microtargets into a detector of the optical particle sensor. In some embodiments, the microtargets on the carrier are designed as described with respect to any of FIGS. 9, 10, and 11 to help reduce capture of light reflected / scattered by the carrier by the detector of the OPS. Process 1200 also includes processing the output of the detector to determine one or more characteristics (such as size) of at least one microtarget on the carrier based on the reflected / scattered light, at block 1209. By comparing the calculated characteristics to known characteristics of the microtarget, a calibration factor can be calculated and used in the OPS during normal operation to improve the performance of the OPS with a correction based on material differences (microtarget vs. expected particles).

[0040] Rotating Carrier The embodiment of the system for testing and calibrating an OPS described above uses a vibrating drive to move a carrier linearly up and down through the measurement volume. In such an embodiment, the finite sample size limits the oscillation frequency and amplitude. Typically, the linear velocity can reach approximately 10 meters per second (m / s). When the oscillation reaches the maximum displacement position, the linear velocity reduces to zero, and the calibration target is outside the sensor measurement volume. Because calibration occurs when the linear velocity reaches its maximum value, the sampling time is relatively limited. Testing and calibration devices based on vibrating a micro-target carrier can be made compact and durable for harsh test conditions, such as testing sensors installed on aircraft. Disadvantages of such solutions include the limited maximum target velocity mentioned above and the possible adverse effects of vibration on test results when larger / heavier carriers containing several sets of micro-targets of different sizes are used. To avoid the above-mentioned drawbacks, a rotating carrier-based solution is proposed, as described below. Rotating carrier-based solutions can provide higher micro-target velocities and are vibration-free, but are significantly more complex than vibrating carrier-based solutions, bulkier, and potentially less durable under harsh operating conditions.

[0041] FIG. 13 is a block diagram of one embodiment of a system 1300 for testing and calibrating an OPS 1308 that enables simulation of particles moving at velocities exceeding 30 m / s. In this embodiment, the system 1300 includes a circular or disk-shaped carrier 1302 having multiple microtargets 1304 formed thereon, arranged concentrically or according to a specific order or pattern. The system 1300 includes a rotary drive 1320 that rotates the carrier 1302 so that the multiple microtargets 1304 rotate around a central axis 1306 of the carrier 1302. The multiple microtargets 1304 on the carrier 1302 have selected particle sizes and shapes to be measured. In a preferred embodiment, sections of the carrier 1302 have a specific sequence of particle sizes, shapes, and orders, which allows for rapid and accurate determination of the sampling range and alignment relative to the measurement volume. Because the particle size is known and can be precisely controlled, and the disk speed is also known, the linear velocity of the multiple microtargets 1304 can also be precisely controlled. Advantageously, system 1300 allows for fast and accurate measurements of particles moving at speeds in excess of 30 m / s, introduces near-zero vibrations, and provides an effective solution that allows multiple calibration micro-targets to be integrated onto a compact carrier.

[0042] Similar to the previous embodiment, system 1300 is designed to test and calibrate OPS 1308. OPS 1308 includes laser 1310 ("transmission optics") and detector 1312 ("receiving optics" 1318). Laser 1310 of OPS 1308 illuminates measurement volume 1316. Particles within measurement volume 1316 reflect / scatter the light from laser 1310 toward OPS 1308. This reflected / scattered light passes through optics 1318 and enters detector 1312, which includes a photodetector that measures the amount of light reflected by any particles present within measurement volume 1316. Detector 1312 generates an output signal based on the photodetector response provided to system 1300 and determines particle size and composition based on this reflected light. Different types of materials may have different reflection amplitudes for the same particle size. To achieve high throughput and accurate measurements suitable for manufacturing and field testing, the system 1300 rotates multiple microtargets 1304 through the measurement volume 1316 at a speed sufficient to simulate real-world conditions.

[0043] In one embodiment, the carrier 1302 (wafer or disk) is mounted on a spindle motor (rotational drive 1320) and rotated at a high speed that can vary between 3,600 and 15,000 revolutions per minute (RPM), which can easily generate consistent linear velocities of over 30 m / s. Note that the speed at which the set of microtargets 1304 moves depends on how far the set of microtargets is located from the center of the disk or wafer on the carrier 1302. For example, the system 1300 moves the microtargets 1304 through the measurement volume 1316 at a selected speed by selectively aligning the microtargets located on the carrier 1302 at the correct distance from the center of the wafer or disk.

[0044] FIG. 14 is a graph showing an exemplary relationship between the linear velocity of the microtarget 1304 and the radius of the rotating wafer or disk (carrier 1302) of FIG. 13. The radius at which the microtarget is formed is plotted along the X-axis, and the linear velocity is plotted along the Y-axis. The various lines 1402-1 through 1402-N reflect the wafer or disk (carrier 1302) rotating at different revolutions per minute (3600 to 15000 RPM). The results show that measurements can be made at sample velocities from 10 to 80 m / s by simply increasing the distance from the center of the disk and the disk rotation speed.

[0045] In one embodiment, the rotation drive 1320 includes a spindle motor that has low power consumption and can be driven to enable RPMs at the values ​​shown in Figure 14. Characterization is performed without the OPS 1308 contacting the rotating sample, and therefore can utilize a reliable source of pre-defined particle sizes and shapes to enable accurate measurements.

[0046] Measurement volume calibration and testing As described above, OPS 1308 is designed to monitor measurement volume 1316 for the presence of particles therein and to properly determine particle type, size, and other characteristics of the particles. System 1300 is designed to test and calibrate OPS 1308 for proper operation in measurement volume 1316 (three dimensions), not just in a plane. To facilitate this function, another embodiment of carrier 1302 is provided by carrier 1500 shown in Figures 15A, 15B, 15C, 15D, and 15E.

[0047] In this embodiment, the carrier 1500 has a conical shape. A plurality of micro targets 1504 are formed on a surface of the carrier 1500 between a base 1501 and an apex 1503 of the carrier 1500. In the illustrated embodiment, the micro targets 1504 are formed in a row between the apex 1503 and the base 1501 of the carrier 1500. The carrier 1500 enables testing and calibration of the entire measurement volume 1316 by moving the carrier 1500 up and down (vertically) so that the laser 1310 of the OPS 1308 is focused on a subset of the plurality of micro targets 1504 as they pass through the measurement volume 1316 at different distances from the OPS 1308. For example, as shown in FIG. 15A , the subset of the plurality of micro targets 1304 represented by micro target 1506 is outside the sensor sampling range 1330 and therefore outside the sensor measurement volume 1316. The laser of the OPS 1308 can illuminate the microtarget 1506 as it rotates on the carrier 1500 and exits the measurement volume 1316. In this example, the location of the microtarget 1506 is 45.00 mm from the OPS 1308. The detector 1312 of the OPS 1308 should not detect the microtarget 1506 from the measurement volume 1316 or should identify it as an invalid measurement.

[0048] As shown in FIG. 15B, as the carrier 1500 moves upward, the microtarget 1508 moves into the sensor sampling range, and therefore into the measurement volume 1316, where it is illuminated by the laser 1310 of the OPS 1308 as the microtarget 1508 rotates through the measurement volume 1316 with the surface of the carrier 1500. In this example, the microtarget 1508 is located 48.90 mm from the OPS 1308. The detector 1312 of the OPS 1308 should detect the calibration target as a valid particle and provide an accurate measurement. The microtarget 1508 is at the edge of the sensor sampling range 1330 of the measurement volume 1316.

[0049] As shown in FIG. 15C, as the carrier 1500 moves upward, the microtarget 1510 moves into the sensor sampling range 1330 and therefore into the measurement volume 1316, where it is illuminated by the laser 1310 of the OPS 1308 as the microtarget 1510 rotates with the surface of the carrier 1500 through the measurement volume 1316. In this example, the microtarget 1510 is located 52.83 mm from the OPS 1308. The detector 1312 of the OPS 1308 should detect the microtarget 1510 as a valid particle and provide an accurate measurement. The microtarget 1510 is in the center of the sensor sampling range 1330 of the measurement volume 1316.

[0050] As shown in FIG. 15D, as the carrier 1500 moves upward, the microtarget 1512 moves into the sensor sampling range 1330 and therefore into the measurement volume 1316, where it is illuminated by the laser 1310 of the OPS 1308 as the microtarget 1512 rotates with the surface of the carrier 1500 through the measurement volume 1316. In this example, the microtarget 1512 is located 56.97 mm from the OPS 1308. The detector 1312 of the OPS 1308 should detect the microtarget 1512 as a valid particle and provide an accurate measurement. The microtarget 1512 is at the edge of the sensor sampling range 1330 of the measurement volume 1316.

[0051] Finally, as shown in FIG. 15E , as the carrier 1500 moves further up, the microtargets 1514 that are outside the sensor sampling range 1330, and therefore outside the measurement volume 1316, are illuminated by the laser 1310 of the OPS 1308. The laser 1310 of the OPS 1308 can illuminate the microtargets 1514 as they rotate on the carrier 1500 and out of the measurement volume 1316. In this example, the microtargets are located 60.94 mm from the OPS 1308. The OPS sensor should not detect the calibration target from the measurement volume 1316 or identify it as an invalid measurement. In this manner, the shape of the carrier 1500 and the arrangement of multiple microtargets 1504 on the carrier 1500 of the system 1300 allow the OPS 1308 to be tested and calibrated throughout the entire measurement volume simply by moving the carrier 1500 up and down.

[0052] 16A, 16B, and 16C show perspective views of another embodiment of a carrier 1600, which allows for testing and calibration of the entire measurement volume 1316 of the OPS 1308 by unidirectional movement (oscillation) of the carrier 1600. The carrier 1600 is formed from multiple concentric cylinders 1602-1 through 1602-N. The multiple concentric cylinders 1602-1 through 1602-N are stacked to simulate a conical shape. Each of the multiple concentric cylinders 1602-2 through 1602-N has a width that is smaller than the width of one of the multiple concentric cylinders 1602-1 through 1602-N with which it is stacked. Additionally, each of the concentric cylinders 1602-1 through 1602-N has micro-targets 1604-1 through 1604-N formed on its respective (e.g., top) surface, near and on the edge of the cylinder. Carrier 1600 and microtargets 1604-1 through 1604-N function in a similar manner as described above with respect to carrier 1500 and Figures 15A-15E to test and calibrate the entire measurement volume 1316. For example, carrier 1600 is configured to be translated 1606 back and forth in a plane parallel to the bases of the plurality of concentric cylinders 1602-1 through 1602-N, which are further configured to rotate about their central axes.

[0053] FIG. 16A shows that micro target 1604-N, a distance A1 from OPS 1308, is illuminated by laser 1310 and reflects / scatters light into detector 1312 of OPS 1308. As carrier 1600 moves in the direction indicated by arrow 1606, micro target 1604-2, a distance A2 from OPS 1308 (as shown in FIG. 16B), is illuminated by laser 1310 and reflects / scatters light into detector 1312 of OPS 1308. As further shown in FIG. 16C, as carrier 1600 moves further in the direction indicated by arrow 1606, micro target 1604-1, a distance A3 from OPS 1308, is illuminated by laser 1310 and reflects / scatters light into detector 1312 of OPS 1308. Distance A1 is shorter than distance A2. Distance A2 is shorter than distance A3. It can be clearly seen that the distance to the sensor can be changed by linear translation of the carrier 1600 .

[0054] FIG. 17A is a perspective view and FIG. 17B is a top view of another embodiment of a disk- or wafer-shaped carrier that enables testing and calibration throughout the entire measurement volume 1316 of the OPS 1308. In this embodiment, the carrier 1700 is formed on a disk or wafer having four portions or sections 1702-1 through 1702-4. Each section 1702-1 through 1702-4 has a different depth (d1, d2, d3, and d4, respectively). Additionally, each section 1702-1 through 1702-4 has multiple targets 1704 formed thereon. As best shown in FIG. 17B, the targets 1704 vary in size and are formed in clusters in concentric rings on the surface of the carrier 1700. Advantageously, the carrier 1700 enables testing and calibration throughout the entire measurement volume 1316 by simply rotating the carrier 1700. No translation is required. The different depths of sections 1702-1 through 1702-4 allow for testing and calibration of OPS 1308 throughout measurement volume 1316, as multiple targets 1704 on sections 1702-1 through 1702-N are at various distances from OPS 1308.

[0055] In this embodiment, carrier 1700 includes three concentric rings 1706-1 through 1706-3 with targets 1704 formed thereon. In other embodiments, any suitable number of concentric rings may be included in carrier 1700. Furthermore, carrier 1700 is positioned relative to OPS 1308 such that measurement volume 1316 covers at least a portion of the concentric rings. Each ring 1706-1 through 1706-N further includes a target 1704 that passes through measurement volume 1316 at a different position in a plane parallel to the XY plane as carrier 1700 is rotated. Furthermore, by having sections 1702-1 through 1702-4 at different heights (along the Z axis), target 1704 also passes through measurement volume 1316 at different distances from OPS 1308. Thus, carrier 1700 moves the targets in three dimensions through measurement volume 1316. To increase coverage of the measurement volume 1316, the targets 1704 on each of the rings 1706-1 through 1706-3 are formed with varying sizes, with the targets positioned at points across the ring to cover a substantial portion of the width of the ring. In the embodiment of FIGS. 17A and 17B , the targets 1704 are shown as clusters of targets of varying sizes. This is shown by way of example and not limitation. It is understood that in other embodiments, the targets 1704 may be formed with other orientations, so long as the targets 1704 allow the carrier 1700 to move the targets through the measurement volume 1316 to test three dimensions of the measurement volume, and the targets 1704 allow the carrier 1700 to move the targets out of the measurement volume 1316 through the laser beam 124 to test the sensor's ability to reject aerosol optical responses from the measurement volume 1316.

[0056] FIG. 18 is a top view of an alternative embodiment of carrier 1800 similar to carrier 1700 of FIG. 17A. Carrier 1800 has eight portions or sections rather than four portions or sections as shown in FIGS. 17A and 17B. The embodiment of FIG. 18 may prove more stable as carrier 1800 rotates by forming sections of similar thickness on both sides of carrier 1800. For example, sections 1802-1 and 1802-5 have similar thicknesses. Other pairs of similar thicknesses include 1802-2 and 1802-6, 1802-3 and 1802-7, and 1802-4 and 1802-8.

[0057] Additional Test Features 13 , in some embodiments, system 1300 also includes functionality and hardware that allows for testing of the health status of OPS 1308, such as lens alignment, laser beam alignment with receiving optics, etc. To accomplish this, OPS 1308 is coupled to computer 1322 that is programmed with functionality 1324 suitable for analyzing the output of OPS 1308 to determine the health status of OPS 1308.

[0058] In one embodiment, the system 1300 is integrated into a calibration tool and includes a short-pulse light source that emulates the optical response of fast particle transitions. The calibration and test system 1300 is capable of generating microtarget velocities of tens of meters per second, while commercial aircraft can reach airspeeds of hundreds of meters per second and military platforms can fly even faster. In one implementation of a commercial aircraft sensor, the optical response peak duration can be as short as 120 nanoseconds. Emulating fast particle transitions by illuminating the detector 1312 with short pulses of light allows for validation of the sensor's ability to respond to the very fast particle transitions that occur during flight.

[0059] In another embodiment, function 1324 of system 1300 includes functionality to assist in determining whether the optical polarization subsystems in the transmitter and receiver of OPS 1308 are functioning properly. The test should include the following two sub-tests: a) Transmitter Test: The system 1300 receives a beam from the laser 1310 and verifies that the laser beam polarization is linear and the polarization plane is oriented as expected. b) Receiver Test: System 1300 transmits linearly polarized light to detector 1312 of OPS 1308, and system 1300 rotates the plane of polarization of the transmitted light to verify that one receiver channel of OPS 1308 receives only s-polarized light and another channel of OPS 1308 receives only p-polarized light.

[0060] In another embodiment, function 1324 of system 1300 includes a function to measure the wavelength of the laser beam received from OPS 1308. This function further analyzes the difference between the target wavelength and the measured wavelength. If the function detects a shift in the wavelength of the laser beam, the function can flag the laser module as aging or damaged.

[0061] In another embodiment, a solar background light source is integrated into system 1300 to enable system 1300 to test the resistance of OPS 1308 to solar background radiation. To this end, system 1300 illuminates OPS 1308 with light from the solar background light source during operation of OPS 1308. Function 1324 of system 1300 includes the functionality to monitor the resistance of OPS 1308 to solar background radiation from the solar background light source integrated into system 1300.

[0062] In another embodiment, functionality 1324 of system 1300 includes functionality to identify a laser beam profile region and its intensity to OPS 1308 .

[0063] In another embodiment, function 1324 of system 1300 includes a function that identifies a shift in the laser beam optical axis position. If the function determines that the shift exceeds a defined threshold, the function triggers an error flag.

[0064] In another embodiment, function 1324 of system 1300 includes a function to verify the laser beam incidence angle. If an optical response is present at a target location where the laser beam should not be positioned, the function flags a possible sensor calibration error.

[0065] In another embodiment, each circular track with the same radius on the carrier 1302 can be further divided into multiple regions with different particle sizes, shapes, and orders, thereby enabling rapid and accurate calibration to be completed.

[0066] It should be noted that the test and calibration methods described herein can be performed only with the aid of external (to the sensor) controlling equipment, with the sensor being controlled / operated by equipment that provides special test-related data to OPS 1308. In other embodiments, special test / calibration firmware may replace the normal operating code stored in OPS 1308 with test / calibration firmware used when testing OPS 1308. When OPS 1308 returns to normal operation, the test / calibration firmware is replaced with the normal operating code.

[0067] The methods and techniques described herein may be implemented in digital electronic circuitry, or with a programmable processor (e.g., a special-purpose processor or a general-purpose processor such as a computer), firmware, software, or combinations thereof. Apparatus embodying these techniques may include suitable input and output devices, a programmable processor, and a storage medium tangibly embodying program instructions for execution by the programmable processor. Processes embodying these techniques may be performed by the programmable processor executing a program of instructions to perform a desired function by operating on input data and generating appropriate output. The techniques may advantageously be implemented in one or more programs executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Generally, the processor receives instructions and data from a read-only memory and / or a random-access memory or other non-transitory computer-readable medium. Suitable storage devices for tangibly embodying computer program instructions and data include, for example, all forms of non-volatile memory, including semiconductor memory devices (such as EPROM, EEPROM, and flash memory devices), magnetic disks (such as internal hard disks or removable disks), magneto-optical disks, and DVD disks. Any of the foregoing may be supplemented by, or incorporated in, specially-designed application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs). [Example]

[0068] Illustrative Embodiments Although specific embodiments have been shown and described herein, it will be understood by those skilled in the art that any configuration which is expected to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any modifications or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.

[0069] Example 1 includes a system for calibrating and testing an optical particle sensor, the system comprising: a carrier having at least one micro-target configured to emulate a particle; a frame configured to receive the carrier, the frame further configured to position the at least one micro-target to pass through a measurement volume of the optical particle sensor; a drive coupled to the frame configured to move the frame such that the at least one micro-target on the carrier moves through three dimensions of the measurement volume such that a light beam from the optical particle sensor is reflected / scattered toward the optical particle sensor; and at least one processor configured to determine one or more characteristics of the at least one micro-target on the carrier based on the reflected / scattered light.

[0070] Example 2 includes the system of example 1, wherein the at least one microtarget comprises at least one reflective line of known width and / or at least one reflective dot of known diameter and / or at least one reflective two-dimensional or three-dimensional structure of known size formed on the layer of optically transparent material.

[0071] Example 3 includes the system of example 2, wherein the at least one reflective line and / or the at least one reflective dot has a triangular cross-section.

[0072] Example 4 includes the system of any of Examples 1-3, wherein the carrier comprises an opening, and the at least one micro-target comprises a wire stretched in free space within the opening.

[0073] Example 5 includes the system of any of Examples 1-4, further comprising an interface adapted to be coupled to a window associated with the optical particle sensor.

[0074] Example 6 includes the system of any of Examples 1 to 5, further comprising a communication interface between the system and the optical particle sensor configured to communicate data between the system and the optical particle sensor.

[0075] Example 7 includes the system of any of Examples 1-6, further comprising a light conditioning subsystem that modifies the light beam incident on the microtarget, the light conditioning subsystem comprising an optical attenuator configured to reduce the incident power of the light beam and / or a half-wave plate configured to rotate the polarization of the light beam by 90 degrees.

[0076] Example 8 includes the system of any of Examples 1-7, wherein the microtargets are positioned to allow testing and calibrating the location and size of the measurement volume of the optical particle sensor, and testing the ability of the optical particle sensor to reject measurements outside the measurement volume.

[0077] Example 9 includes the system of any of Examples 1-8, wherein the drive is configured to change the frame position within the measurement volume while the carrier rotates.

[0078] Example 10 includes the system of example 9, wherein the carrier has a conical shape, and the at least one microtarget includes a plurality of microtargets arranged in a row between an apex and a base of the carrier.

[0079] Example 11 includes the system of example 10, wherein the conical shape of the carrier is implemented as a stack of concentric cylinders that decrease in size from the bottom to the top of the carrier.

[0080] Example 12 includes the system of example 11, wherein the at least one microtarget includes a microtarget formed on a top surface of each of the concentric cylinders near an edge of the concentric cylinder.

[0081] Example 13 includes the system of example 11, wherein the carrier is configured to translate in a plane parallel to a base of the stack of concentric cylinders, and the stack of concentric cylinders is further configured to rotate about a central axis of the stack of concentric cylinders.

[0082] Example 14 includes a system for calibrating and testing an optical particle sensor, the system comprising: a disk-shaped carrier having a substantially circular surface facing the optical particle sensor, the carrier divided into a plurality of sections, each section having a height such that the surface of each section passes through a measurement volume of the optical particle sensor at a selected distance from the optical particle sensor, the carrier further comprising a plurality of concentric rings, each of the plurality of concentric rings having a plurality of micro-targets formed within the concentric ring on the surface of the carrier, the micro-targets being configured to emulate particles; a drive coupled to the carrier configured to rotate the carrier such that at least some of the plurality of micro-targets on the carrier move through three dimensions of the measurement volume such that a light beam from the optical particle sensor is reflected / scattered toward the optical particle sensor; and at least one processor configured to determine one or more characteristics of at least one micro-target on the carrier based on the reflected / scattered light.

[0083] Example 15 includes the system of example 14, wherein the plurality of micro-targets on the concentric rings are formed into a plurality of clusters of micro-targets, each of the plurality of clusters of micro-targets including micro-targets of various sizes.

[0084] Example 16 includes the system of example 15, wherein the micro-targets are formed at points across the concentric rings to cover a substantial portion of the width of the concentric rings.

[0085] Example 17 includes the system of any of Examples 14-16, further comprising an interface adapted to be coupled to a window associated with the optical particle sensor.

[0086] Example 18 includes the system of any of Examples 14 to 17, wherein the carrier has an even number of sections, each of the plurality of sections is paired with another section of the plurality of sections, the paired sections have equal heights and weights and are located directly opposite each other.

[0087] Example 19 includes the system of any of Examples 14-17, wherein the height of each section is selected to enable testing and calibrating the full depth of the measurement volume of the optical particle sensor, and testing the ability of the optical particle sensor to reject measurements from the sensor measurement volume.

[0088] Example 20 includes the system of any of examples 14-19, wherein the radius of the carrier is selected to enable simulation of particles of a selected velocity.

Claims

1. 1. A system (100, 1300) for calibrating and testing an optical particle sensor (102, 1308), comprising: a carrier (116, 1302) having at least one microtarget (113, 1304) configured to emulate a particle; a frame (118) configured to receive the carrier, the frame being further configured to position the at least one micro target to pass through a measurement volume (108, 1316) of the optical particle sensor; a drive (120, 1320) coupled to the frame, configured to move the frame such that the at least one micro-target on the carrier moves through three dimensions of the measurement volume such that a light beam from the optical particle sensor is reflected / scattered towards the optical particle sensor; and at least one processor configured to determine one or more characteristics of the at least one microtarget on the carrier based on the reflected / scattered light.

2. The at least one micro-target is 10. The system of claim 1, comprising at least one reflective line of known width, and / or at least one reflective dot of known diameter having a flat surface parallel to the surface of the carrier or inclined at an angle to the surface of the carrier, and / or at least one reflective two-dimensional or three-dimensional structure of known size formed on a layer of optically transparent material.

3. 10. The system of claim 1, comprising a two-dimensional or three-dimensional structure that allows controlled movement of micro-targets in two or three dimensions while the carrier is rotated about an axis of symmetry perpendicular to a surface of the carrier containing the micro-targets or translated along an axis parallel to the surface of the carrier containing the micro-targets.

4. the carrier includes a disk-shaped carrier having a substantially circular surface facing the optical particle sensor; the carrier is divided into a plurality of sections, each section having a height such that a surface of each section passes through a measurement volume of the optical particle sensor at a selected distance from the optical particle sensor; the carrier further includes a plurality of concentric rings, each of the plurality of concentric rings having a plurality of micro-targets formed within the concentric ring on the surface of the carrier, the micro-targets configured to emulate particles; 2. The system of claim 1, wherein the drive unit is configured to rotate the carrier such that at least some of the plurality of micro targets on the carrier move through three dimensions of the measurement volume, causing a light beam from the optical particle sensor to be reflected / scattered toward the optical particle sensor.

5. The system of claim 4 , wherein the plurality of micro-targets on the concentric rings are formed into a plurality of clusters of micro-targets, each of the plurality of clusters of micro-targets including micro-targets of different sizes.

6. The system of claim 4 , wherein the micro-targets are formed at points across the concentric rings so as to cover a substantial portion of the width of the concentric rings.

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