7 Understanding Measurement Strategy
MVR systems can be operated with any of six telecentric fixed-focus lenses with magnification from 0.30X to 4.0X or with 6.5:1 zoom optics with continuously adjustable magnification from 0.7X to 4.5X. Magnification is the image size at the camera CCD detector place divided by the object size. Since the CCD size is fixed (namely 9.93 x 8.70 mm for the 2 Mpixel camera), each magnification has a corresponding field of view (FOV), which is the CCD size divided by magnification. The higher the magnification, the higher the resolution but the smaller the field of view.
Note that the centering of the optics can vary by a small amount in the quick-change bayonet optics mount, so all measurements on the same part need to be taken with the same optics.
7.1 Telecentric Lens Measurement Strategy
Select telecentric optics to perform high accuracy, high throughput field-of-view (FOV) measurements. If all measurements are to be in the FOV, select the highest magnification lens whose FOV encompasses the entire part. The 0.30X lens accommodates parts up to 51 x 38 mm (2.00 x 1.50 inches). If the entire part cannot fit into the FOV, move the stage by up to 200 mm (8 inches) for the MVR200 or 300 mm (12 inches) for the MVR300, and the M3 software will seamlessly integrate FOV measurements with encoder readings from stage motion.
7.2 Zoom Optics Measurement Strategy
The 6.5:1 zoom optics allows magnification to be continuously adjusted from 0.7X to 4.5X. While the zoom optics can provide the same FOV as the four higher magnification telecentric lenses, they do not offer the same low optical distortion that is required for accurate FOV measurements across the entire FOV. However, they are equally as accurate as telecentric lenses when used at high magnification in combination with stage motion. Select zoom optics to measure large parts which would not fit into a single FOV, also for smaller parts where extremely high magnification is required. The lowest zoom magnification setting accommodates parts up to 11.2 x 9.4 mm (0.44 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 will ensure that a feature will remain at the optical center of the video image throughout the magnification range.
7.3 Illumination Strategy
Once the image has been properly focused and magnification has been set, adjust light levels as necessary using the slider controls in M3 software. The right lighting is paramount to accurate measurement with any video-based measurement system. Lighting that is too low will result in a dark, low-contrast image with indiscernible features. Lighting that is too bright may 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, 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 change light
Made with FlippingBook - professional solution for displaying marketing and sales documents online