Surface Finish and the Fotonic Sensor - MTI Instruments - #1

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MTI Instruments, Inc. 325 Washington Avenue Extension Albany, NY 12205 PH: +1-518-218-2550 OR USA TOLL FREE: 1-800-342-2203 FX: +1-518-218-2506 sales@mtiinstruments.com www.mtiinstruments.com APPLICATION NOTE Surface Finish and the Fotonic Sensor Introduction MTI Instruments has run a series of experimental tests using a standard MTI-1000 Fotonic Sensor looking at various surface fi nish samples. These tests were conducted by adjusting the MTI-1000 for normal operation against a 2-L surface; and then without changing this adjustment, other surface samples were substituted. 2L is a fi nely lapped, mirror-like surface. The additional samples were 8L, 16G, 63G, 63P, and 125M. These are considered “standard” surface fi nish reference numbers used throughout the machine tool industry and represent a wide variation in fi nishes. Preparation When using the Fotonic Sensor to measure smoothness or surface fi nish, the probe is usually separated from the target (specimen) at a distance which puts the standard Fotonic Sensor curve at its output peak. The output is comparatively insensitive to displacement resulting from non-fl at surfaces or slight deviation from true perpendicularity of the probe. The Fotonic Sensor then becomes sensitive only to smoothness or color changes. Surfaces under observation should be clean and free from oil, rust and dirt. The calibration standards should be of the same general color as the item to be observed. Since no carrier frequencies are used in the electronics and the frequency response of the pickup goes as high as 2 MHz; it is possible to scan larger surfaces faster. In-line examination of the entire surface of all parts is also practical. The Fotonic Sensor can detect surface scratches smaller than a microinch wide or deep. Without motion, the instrument may integrate smoothness over the entire area being viewed Advantages Over Stylus Measurements Fotonic Sensors have several fi ber optic arrangements and each have somewhat different capabilities. It is possible to measure smoothness without even moving the probe or part; whereas motion is necessary with stylus measuring means. Since most surfaces have a different roughness in different planes or directions, it is often diffi cult to say just what overall fi nish actually is. A groove may have a very smooth bottom in which the stylus rides - and a very rough side and peak. The roughness of a surface may vary over several orders of magnitude when measured with a stylus, depending upon the direction of measurement. MTII appnote: fotonicsmoothness.pdf - page 1 of 2