GAR Precision Reference Standard
The GAR Precision Reference Standard provides and economical calibration tool which permits the technician to calibrate surface analyzing equipment to its peak efficiency. The Precision Reference Standard is rectangular in shape, (2-1/2" x 3-3/4"), it is made of electroformed nickel and is rhodium plated for superior abrasion resistance. It is supplied in a leather case and includes certification traceable to N.I.S.T.
The surface of the Precision Reference Standard consists of a series of parallel, uniform, "V-shaped" grooves having an included angle of 150 degrees between the sides. Since the surface character of the Precision Reference Standard is unlike normally machined surfaces, it is not recommended for use in visual and tactual comparison.
Method of Calibration used reported by N.I.S.T.
The patch mean values identified on the border of the standard is the roughness average (Ra) obtained from five measurements taken in the areas defined in the sketch shown. The sketch applies to both patches by simply rotating the standard 180 degrees. These values represent the average surface roughness of each trace using 0.0004" (0.010mm) radius diamond stylus and a 0.030" (0.8mm) roughness width cutoff, in accordance to the American National Standards Institute (ANSI) specification titled: "Surface Textrue, Surface Roughness, Waviness and Lay" ANSI/ASME B46.1
The Specimen under test was calibrated by a one-step transfer from the appropriate master using a stylus type instrument. Five measurement were made over each of five areas distributed over the whole
PATCH MEAN VALUE
AREA NO. | 16.10 microinches* | 119.5 microinches |
1 | 16.20 | 119.40 |
2 | 16.20 | 119.16 |
3 | 15.66 | 118.10 |
4 | 16.00 | 119.63 |
5 | 16.26 | 119.50 |
* This patch is intended only for indicating the effective size of the diamond stylus.
Reports of Calibration by U.S. Department of Commerce, National Institute of Standards and Technology
The property of surface roughness in the 125 microinch range and below is maintained by N.I.S.T. by means of master roughness specimens conforming to ANSI B46.1. The master specimens were calibrated by measuring their surface profile with a stylus instrument which in turn was calibrated by a interferometrically measured step. The areas under the profile curves were then measured and the roughness average computed. The accuracy of this measurement is 2% for the 119.5 and 1 microinch for the 16.1.
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