Focusing shadowgraph is an optical measurement device based on the principle of light refraction, used to visualize density gradient changes in transparent media (such as gas flow, thermal convection, etc.). Its installation requires a combination of mechanical stability, optical path alignment, and electrical safety. The following is a detailed step-by-step installation process:
1、 Preliminary preparation and equipment inspection
1. List of Tools and Materials
-General tools: wrench, screwdriver, level ruler, laser pointer (or crosshairs), tape measure, gloves, dust cloth.
-Special accessories: adjustable bracket, reflector frame, focusing lens group, blade assembly, light source (LED/laser), power cord, data acquisition system (CCD camera or photoelectric sensor).
-Auxiliary equipment: computer (pre installed control software), grounding wire, blackout curtain.
2. Equipment inspection
-Check whether all optical components (such as mirrors, lenses, and cutting edges) are clean and free of scratches, and clean them with lens paper if necessary.
-Check the brightness and uniformity of the light source to ensure there are no flickering or dark areas.
-Verify the integrity of mechanical components such as brackets and guide rails, and match the threaded hole positions.
2、 Mechanical structure assembly
1. Platform construction and horizontal adjustment
-Place the main support platform on a stable desktop or experimental platform, and adjust it to a horizontal position using a spirit level (with an error of<0.5 °).
-Fix the light source module at one end of the platform, ensuring that the light source emission end is perpendicular to the optical axis (adjustable with the assistance of a laser pointer).
2. Installation of Light Path Pillars
-Layout the pillars according to the design drawings, with spacing that meets the optical path length requirements (typical schlieren system optical path length is 0.5-2 meters).
-Use an adjustable bracket to install the reflector (tilted at 45 °), ensuring that the center of the mirror surface coincides with the optical axis.
3. Positioning of key components
-Blade component: placed behind the last reflector, the blade direction should be perpendicular to the optical axis, and the precise movement of the blade position (used to adjust sensitivity) can be achieved by adjusting the screw.
-Focusing lens group: installed 10-20 cm in front of the blade, the focal length of the lens needs to match the size of the measured field (for example, a 50 mm lens is suitable for small-scale flow fields).
-Imaging screen/camera: located at the focal plane of the lens, ensuring that the CCD target surface is perpendicular to the optical axis.
3、 Optical path alignment and debugging
1. Coarse dimming path
-Turn on the light source and observe whether the light passes through the centers of each reflector in sequence. If there is a deviation, the pitch angle and horizontal angle of the mirror frame need to be adjusted.
-Place a grid target (or white screen) in front of the blade and preliminarily check whether the shape of the light spot is symmetrical.
2. Fine collimation
-Mirror adjustment: By using a laser beam or a crosshair target, adjust the mirrors one by one to make the incident light and reflected light strictly coincide (verified using the "back and forth reflection method").
-Lens coaxial calibration: Move the imaging screen back and forth until the light spot is clear and there is no vignetting effect, then lock the lens holder.
-Blade alignment: Fine tune the blade to the center of the light spot and observe whether the boundary between light and dark on the imaging screen is sharp.
3. Focus on verification
-Place the test sample (such as the air layer above the heating plate), adjust the distance between the lens and the cutting edge until clear flow field refractive fringes are observed.
-If the stripes are blurred, the focal length of the lens or the inclination angle of the cutting edge can be adjusted (usually the angle between the cutting edge and the optical axis is ≤ 5 °).
4、 Electrical and software configuration
1. Line connection
-The light source is connected to a regulated power supply, and the grounding wire is reliably connected to avoid electromagnetic interference.
-The camera is connected to the computer via USB or Ethernet cable, and the accompanying driver software (such as Image Pro Plus, NI LabVIEW) is installed.
2. Parameter settings
-Light source adjustment: Adjust the brightness to the appropriate value (to avoid overexposure), and the laser light source should be evenly illuminated with a beam expander.
-Camera parameters: Set exposure time (typical value 10-100 ms), resolution (≥ 1024 × 1024 pixels), and trigger mode (continuous/single frame).
-Blade control: If it is an electric blade, the blade movement speed (usually 0.1-1 mm/s) needs to be set in the software.
5、 System calibration and testing
1. Benchmark calibration
-Remove the sample and take a background image using a uniform medium (such as still air) as a reference benchmark.
-Adjust the blade position to ensure that the background brightness uniformity error is less than 5%.
2. Function verification
-Dynamic testing: Introduce disturbance sources (such as blowing air or heating plates) and observe whether the deformation of the stripes meets physical expectations (such as the upward bending of the stripes caused by the rise of hot air).
-Resolution testing: Use standard interference fringe plates or resolution targets to evaluate the spatial resolution of the system (usually requiring 10-20 line pairs/mm).
3. Data recording
-Save images under typical operating conditions (such as. bmp or. tif format), and annotate experimental conditions (such as ambient temperature, light source intensity, etc.).
-Analyze the displacement of stripes through software and convert the density field distribution (combined with calibration formulas).