terior diameter will be in focus at all times. On larger diameters, the instrument would have to be tipped slightly to focus on a specific area of sidewall. The instrument is suitable for viewing parts from 1 inch to 20 feet in length. The focus can be adjusted by holding the instrument in one hand and turning the zoom with the other hand for sharper definition of any depth of field. The area is sharp and in focus at any given focal plane and will vary from about 6 inches to 5 feet, depending on the length of the part and distance from the instrument. For more detail beyond 5 feet, a magnification booster is available. The zooming borescope does not have its own light source, but relies on existing ambient light. Unless the part is very small in diameter, or standard room illumination is poor, no additional light source is necessary. should additional light be necessary, an inspection flashlight (see Table 3-8) can be held against the other end of the part.
FIGURE 4-13. ZOOM-A-BORE INSPECTION INSTRUMENT WITH
MAGNIFICATION BOOSTER ATTACHED (Courtesy of Titan Tool Supply Company, Inc.)
(8) Micro-Bore Viewing System. Small area borescope viewing systems exist for optical checking of bores and cavities (see Figure 4-14). This system does not fit the definition of a rigid borescope; however, it is used for inspection of bores and cavities. The system was designed to overcome the lighting limichap 4 Page 136 Par 404
tations of some of the micro-borescopes and will not break as easily as the small-diameter borescope probes. This optical device in the illustration comprises 17 different lenses on a rotary system, each with a predetermined focal length (minimum of
0.020 inch to a maximum of 10 inches). It can be used for the internal viewing of micro-bores, tubes, and cavities from 0.039 to 0.315 inch diameter, with depths up to 10 inches. The illumination system is adjustable and contains a 2.5 volt Halogen light bulb. For deep cavities, additional illumination may be necessary, which can be provided by a small diameter inspection light.
FIGURE 4-14. MICRO-BORE VIEWING SYSTEM (Courtesy of Titan Tool Supply Company, Inc.)
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The micro-bore viewing system can be used in aircraft maintenance for checking the inside of small tubes, miniature drilled, bored, and ground holes for surface finish, cracks, dirt, weld cracks, porosity, etc. It can also be used for inspecting the inside of miniature holes in turbine blades and valve bodies.
(9) Mirror Tube Viewing Systens. These systems allow the viewing of small holes and cavities and are meant to be inexpensive alternatives to a rigid borescope for some applications.
The system shown in Figure 4-15 allows the viewing of holes and cavities to a depth of 2 inches with 5-power magnification without any attachments. Included with the unit are two separate twist-on mirror tubes, a 0.196 inch diameter, with a viewing depth of 1 inch, and 0.236 inch diameter, which allows a viewing depth of 1.2 inches. Illumination is provided by a miniature Halogen light bulb projecting the illumination directly on the axis down the hole. Powered by two AA batteries.
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90° Viewing FIGURE 4-12' (courtesy of Titan Tool Supply MIRROR TUBE VIEWING SYSTEM Company, Inc.)
The mirror viewing system shown in Figure 4-16 is for viewing holes up to 68 inches in depth. The main probe can be 4 to 20 mm in diameter. The field of view is 30 to 70 degrees.
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AC 43—204 8/14/97 FIGURE 4-16. DEEP-HOLE MIRROR VIEWING SYSTEM (Courtesy of Instrument Technology, Inc.)
Flexible Borescopes. Flexible borescopes are generally used in applications that do not have a straight line access path to the area to be inspected. Some typical uses of flexible borescopes in aircraft maintenance are inspection of corrosion, Chap 4 Page 140 Par 404
cracks, and scratches on bore walls of castings; inspection for corrosion and cracks of wing stringers, wing attachment fittings, spars, and other aircraft structural members; inspection of engine cylinder sleeves, pistons, and valves for damage; and inspection of aircraft turbines for cracks, corrosion, damage by foreign objects, and erosion. The two types of flexible borescopes are flexible fiberscopes and flexible videoscopes.
Figure 4-17 shows some typical flaws seen through a flexible fiberscope D FIGURE 4-17. TYPICAL FLAWS SEEN THROUGH A FLEXIBLE FIBERSCOPE (Courtesy of Olympus Corporation) Chap 4 Par 404 Page 141
Flexible Fiberscopes. A typical flexible fiberscope consists of a fiber-optic light-guide bundle, a fiber-optic image-guide bundle, an objective lens, interchangeable viewing heads, and remote controls for articulation of the distal tip.
Flexible fiberscopes are available in diameters from 0.055 to 0.5 inch and in lengths of over 300 feet. The light-guide bundle is used to carry illumination from a remote source to the distal Since each fiber in the light-guide bundle transmits only illumination and not an image, the fibers do not have to be precisely aligned and are generally larger than those in the imageguide bundle. The image-guide bundle is used to carry the image formed by the objective lens back to the eyepiece, and the fibers in the image guide are precisely aligned so that they are in an identical relative position to each other at their terminations for proper image resolution. The diameter of the fibers in the image guide is a factor in obtaining good image resolution.
large number of small-diameter fibers in the image-guide will provide a bright image with high resolution (see Figure 4-18).
lich resolution allows the use of an obiective lens with a wider field of view and also allows magnification of the image at the eyepiece for better viewing of objects at the periphery of the image (see Figure 4-19). Interchangeable distal tips provide various directions and fields of view on a single fiberscope;
however, because the tip can be articulated for scanning purposes, distal tips with either a forward or side viewing direction are usually sufficient. Fields of view are typically 40 to 60 degrees, although they can range from 10 to 120 degrees. Most fiberscopes provide adjustable focusing of the objective lens.
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8/14/97 AC 43-204 Two views down a combustar con with the datal tip in the some pastion. A fiberscope with smaller diameter fibers and 40% more fibers in the image bundle provides better resolution (a) than a fiberscope Riben (b). Courtesy of Olympus Corporation FIGURE 4-18. COMPARISON VIEWS WITH DIFFERENT QUANTITIES OF
FIBERS IN THE FIBERSCOPE IMAGE BUNDLE (Courtesy of Olympus Corporation) chap 4 Par 404 Page 143
8/14/97 AC 43-204 ENGINE SN • 709100 * USAIR * J180 NEV CAN • 7 08/84/87 12:20:09 ENCINE SN # 709100 * USAIR * TTBD FUEL NOZZLE 08/04/87 12:58:25 0:19:05 FIGURE 4-19. FLEXIBLE VIDEOSCOPE IMAGES (Courtesy of Welch Allyn, Inc.)
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Flexible Videoscopes With CCD Probes. Flexible videoscopes have CCD imaging sensors at the distal tip to electronically transmit color or black and white images to a video moni- The fiber-optic image bundle inside the insertion tube is replaced by a wire assembly to carry video information. Videoscopes with CCD imaging sensors produce images with spatial resolutions on the order of those described in Figure 4-20.
90° FIELD OF VIEW 60° FIELD OF VIEW 30> FIELD OF VIEW UMM LIN. UMM LIM. UMM LIN.
102 T - USEABLE 4020 USEABLE ISEABLE - RESOLUTION 300 RESOLUTION 300 RESOLUTION 300 200 200 100 100
• ~ 20 80 100 40 6D 10%
OBJECT DISTANCE MM OBJECT DISTANCE MM OBJECT DISTANCE MM WIN. = Lines per inch UMM = Lines per millimeter SHARP FOCUS FIGURE 4-20. TYPICAL CCD VIDEOSCOPE RESOLUTION (Courtesy of Welch Allyn, Inc.)
The resolution of videoscopes, like rigid borescopes and flexible fiberscopes, depends on the object-to-lens distance and the field of view, since these two factors affect the amount of magnification. Generally, videoscopes produce higher resolution than fiberscopes, although riberscopes with smaller diameter fibers can be competitive with the resolution of videoscopes. A primary advantage of videoscopes is their longer working length. with a given amount of illumination at the distal tip, videoscopes can return an image over a greater length than fiberscopes.
features of videoscopes include (1) the display can help reduce eye fatigue (but does not allow the capability of direct viewing through an eyepiece); (2) there is no honeycomb pattern or irregular picture distortion as with some fiberscopes (see Figure 4-21); (3) the electrical image signal allows digital image enhancement and the potential for integration with automatic inspection systems; and (4) the display allows the generation of reticles on the viewing screen for point-to-point measurements.
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• FIGURE 4-21. COMPARISON BETWEEN VIDEOSCOPE AND FIBERSCOPE IMAGES (Courtesy of Welsh Allyn, Inc.)
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Borescopes With Special Features. Borescopes, fiberscopes, video systems, and related equipment are being used for more purposes, more complex inspections, and even some limited repair applications. Some of the borescope products briefly described are measuring borescopes and fiberscopes, working channels, flying probe, VideoHook Probe, power blending borescope, and ShadowProbe™.
(1) Measuring Borescopes and Fiberscopes. Measuring borescopes and fiberscopes contain a moveable cursor that allows measurements during viewing (see Figure 4-22). When the object under measurement is in focus, the movable cursor provides a reference for dimensional measurements in the optical plane of the This capability eliminates the need to know the objectto-lens distance when determining magnification factors. Measuring borescopes and fiberscopes can be used in aircraft maintenance for measuring cracks in aircraft turbine liners, blade damage, etc.
FIGURE 4-22. VIEW THROUGH A MEASURING FIBERSCOPE (Courtesy of Olympus Corporation) Working Channels. Working channels are used in borescopes and fiberscopes to pass working devices to the distal Figure 4-23 shows a retrieval tool in a working channel picking up a screw inside a machine. Table 4-3 shows some typical devices for use in working channels. working channels are presently used to pass measuring instruments, retrieval devices, and hooks for aiding the insertion of thin, flexible fiberscopes.
working channels are used in flexible fiberscopes with diameters Chap 4 Par 404 Page 147