6. MEASUREMENT STRATEGY
HVR systems include a .090X telecentric lens. Magnification is the image size at the camera charge coupled device (CCD) detector divided by the object size. For example, a 2.0-inch circle would be .18-inches on the CCD array (2.0 x .090=.18). This value is different than total magnification, which is the size of the object on the monitor.
6.1 Measurement Accuracy and Depth of Field
The telecentric lens included with the system provides high accuracy, high throughput field-of-view (FOV) measurements. The 0.090 lens accommodates parts up 92.7 mm x 76.2 mm (3.65 x 3.0 inches).
Accurate measurement requires proper focus of the image. When measuring flat parts, always ensure that the stage glass has been leveled.
Always work at best focus. Telecentric lenses have a large focus range, also known as depth of field. Within this range, the instrument is expected to measure wi th an accuracy of approximately 10 microns or better for a one-inch object. The most repeatable results can be achieved by taking the time to adjust focus using digital zoom. Focus is determined by digitally zooming in on the edge of an object and adjusti ng focus until the pixels appear on that edge. This ensures the best and most repeatable measurements are obtained. See the figures below that illustrate poor focus and good focus.
Note:
For best results, view these figures online with a high-resolution monitor. A printed version of these figures does not provide a clear distinction of difference between good and poor focus.
Example of Object with Poor Focus
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