7 Measurement Strategy The KMR Mx200 is available with 6.5:1 zoom optics with adjustable magnification from 0.7X to 4.5X. As used here, magnification is the image size at the camera CMOS detector place divided by the object size. Since the CMOS size is fixed, each magnification has a corresponding field of view (FOV), which is the CMOS size divided by magnification. The higher the magnification, the higher the resolution, but also the smaller the field of view. 7.1 Zoom Optics Measurement Strategy Zoom optics are ideal to measure large parts which would not fit into a single FOV, also to measure smaller parts where extremely high magnification is required. The lowest zoom magnification setting accommodates parts up to 11.2 x 9.4 millimeters (0.44 inches x 0.37 inches) in the FOV. To measure large parts, locate the edge of interest at minimum magnification, then take the actual measurement at maximum magnification using the system's crosshairs. The zoom optics’ parcentricity feature ensures that a feature will remain at the optical center of the video image throughout the magnification range. In general, higher magnification provides greater resolution and accuracy; however, not all features should be inspected at the highest available magnification. Too high a magnification might make it difficult to discern edges by exaggerating edge defects such as burrs or chips. Try decreasing the magnification until the edge is more clearly identifiable. Also consider factors such as tolerance requirements, manufacturing processes, functional requirements and optical characteristics of the part. Features with loose tolerances might not need to be inspected at high magnification. Select the magnification best suited for the requirements. 7.2 Illumination Strategy Once the image has been properly focused and magnification has been set, adjust light levels as necessary using the light controls on the System Controller. The right lighting is paramount to accurate measurement with any video-based measurement system. Lighting that is too dim will result in a dark, low-contrast image with indiscernible features. Lighting that is too bright might result in a washed-out image and blooming, or oversaturated bright regions that distort features. When adjusting lighting, start with light that is lower than desired, and then increase lighting while viewing the image on the monitor. Maintain constant lighting for consistent results. Always use the same light level while sampling points for a single feature – do not to change light levels during a measurement run. Depending on the part characteristics and the feature being viewed, the right combination of lighting might aid in bringing out a particular feature. Take time to experiment by balancing the available light sources. 7.3 Magnification and Focus Strategy Accurate measurement requires proper focus of the image. With a zoom lens, focusing is most sensitive at highest magnification. A good strategy is to first focus the image at the highest magnification, and then decrease magnification to the desired level. In general, high magnification (or zoom) helps with accurate measurements. However, while high magnification provides high resolution, it does not always provide the highest accuracy, and not all features should be inspected at the highest available magnification. Too high a magnification might make it difficult to discern the edge of a feature by exaggerating edge defects such as burrs and chips. Try decreasing the magnification until the edge is more clearly definable. Also, there is an inverse relationship between magnification and field of view; using a lower magnification might be more convenient.
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