Instrument calibration specimens of regular geometrical surface profile can be calibrated. Roughness comparison specimens and roughness can be made in accordance with USASI B46.1.

measurements

Instrument calibration specimens for surface roughness measuring equipment having regular geometrical surface profiles can be calibrated by comparison with NBS reference specimens or by graphical analysis.

Roughness measurement of roughness comparison specimens or of other surfaces can be measured in accordance with USASI B46.1, using our instrumentation.

212.227.2z Surface roughness measurements are made as special tests.

212.228 Angular standards.

Fixed angular standards having flat defining surfaces can be calibrated by autocollimation and interferometric techniques.

212.228.1 Angle gage blocks.

Angle gage blocks are calibrated using autocollimation techniques. Squares used as angle gage blocks are considered to be polygons having 4 sides, 212.228.2a.

212.228.la One gage block of 1, 3, 5, 20, or 30 seconds; 1, 3, 5,

20,

or

minutes; or 1, 3, 5, 15, 30, or 45 degrees nominal sizedetermination of flatness of faces, squareness to sides, and angle between faces. Accuracy of angle determination is within ±0.5 second.

212.228.1b Angle gage block set of 16 blocks calibrated as in item a. 212.228.1z Special measurements not covered by this schedule.

The calibration of polygons is done with autocollimation chniques. It consists of the determination of flatness of each face, riation of the angle between each face and the base (where possible the lygon will be adjusted for minimum variation), and the angle between ces. The accuracy of the angular values determined is within ±0.5

212.228.3 Solid angle calipers and step mirrors.

The solid angle calipers and step mirrors are calibrated by utocollimation or interferometric techniques as to the angle between

12.228.3z Angle calipers and step mirrors are calibrated as special

measurements.

212.228.4 Fixed refractive angular standards: Wedges.

Wedges are calibrated by by autocollimating or interferometric echniques at a specified wavelength for deviation angle.

Item

Description

12.228.4z Wedges are calibrated as special measurements.

212.228.5 Mechanical angular references.

Mechanical angular references such as cylindrical squares achinist's squares usually are calibrated by mechanical techniques.

and

212.228.5z Mechanical angular standards and tools are calibrated as special measurements.

212.229 Angular measuring and setting instruments.

Direct inquiries to, and mark shipments for the attention of: Engineering Metrology Section, MET - A107, National Bureau of Standards, Washington, DC 20234. Telephone: 301-921-2140.

Instruments and tools used for the precise measurement of angle, such as precision angular rotary and indexing tables, autocollimating telescopes, or angle generating equipment, are calibrated. 212.229.1 Precision angular rotary and indexing tables.

Rotary and indexing tables are calibrated for angular motion at specific angular settings.

212.229.1z Angular rotary and indexing tables are calibrated as special measurements.

settings.

Item

212.229.2 Autocollimating telescopes.

Autocollimating telescopes are calibrated at specific angular

Description

212.229.2z Autocollimating telescopes and similar devices are calibrated as special measurements.

212.310 General.

(a) Direct inquiries to, and mark shipments for the attention Mass and Volume Volume Metrology Branch, MET B116, National Bureau of ndards, Washington, DC 20234. Telephone: 301-921-2511.

support the or

(b) The Mass and Volume Branch provides services to ments of the national measurement system which rely directly irectly on mass measurements. These services include the calibration of erence standards of mass, of glass and metal volumetric reference ndards, and of reference standard hydrometers, also the density erminations of solids and liquids, and are offered only if suitable vice is not available otherwise. In order to provide prompt and useful vice, the acceptance of the items for calibration or test is based on scussions with each user to determine details necessary to meet asurement and delivery requirements, and on inspection of the item at the reau with reference to its suitability for the usage intended. Sections 2.311, 212.312, and 212.313 apply to the calibration (or test) most equently requested in each measurement area. The services of the Branch, wever, are not limited to these specific items. Inquiries are invited cerning other measurement problems in the above areas.

(c) Additional services are available which include the formution of procedures (1) to establish a quantitative measure of the state statistical control in the user's laboratory for measurement processes ich involve mass, (2) to enable the user to monitor his calibration ocess, and (3) to assist in coordinated evaluation of the results. The ture of these services is described in NBS Technical Note 288, "Measuret Philosophy of the Pilot Program for Mass Calibration."

(d) Arrangements for calibration (or test) must be completed fore shipping apparatus to the Bureau. While al1 of the work of the anch is on an actual cost basis, subject to a $25 minimum charge, a cual agreement on the work to be performed generally results in subantial savings for the user. Detailed packing and shipping instructions e available on request. Items not accepted for calibration or test will returned, the cost of inspection or the minimum charge will be

plicable.

(e) The results of a calibration or test will be reported either a National Bureau of Standards Report of Test (which in many cases is epared by a computer program), a continuation report, or a letter report. each of these, the values reported are accompanied by an appropriate imate of uncertainty (allowance for random and systematic errors) as termined by an analysis of the specific measurement process. A continuaon report is used for those items submitted for recalibration on which eliminary tests indicate that no significant changes have occurred since e last calibration. Usually a letter report is used to report a test for pliance with a specification which states limits for the departure of

e actual value from nominal.

212.311 Reference standards of mass.

(a) The Bureau's calibration of reference standards of mass proles extensions of the mass unit embodied in the NBS standards of mass. A mal calibration consists of establishing a mass value, and the apopriate uncertainty for that value, for each weight which has been

that a weight meet the adjustment tolerances established for Classes A, M, or S-1 (as described in Circulars 3 and 547, Volume III, of NBS Handbook 77*) prior to submission. Normally Normally weights are available from manufacturers, many of whom can furnish directly documentation suitable for meeting quality assurance contracts and requirements.

to

(b) Individual weights, or sets of weights, in the range of 30 kilograms to 1 milligram or 50 pounds to 1 micropound in decimal subdivisions, which are designated as reference standards, must be of design, material, and surface finish comparable to but not necessarily limited present Classes A, B, M, S, or S-1. Design, material, and surface finish of large mass standards (over 50 lb to 50,000 lb) must be compatible with the intended usage. For these large mass standards, an adjustment with reference to a nominal or desired value can be included as a part of the calibration procedure.

on

(c) The values of true mass (and an apparent mass correction) included in the report will be determined by using computed volumes based the manufacturer's statement of density of the material, on the density computed from measured volumes, or, in the absence of this information, on estimated density values. The apparent mass corrections are computed for 20 °C with reference to Normal Brass (density 8.4 g/cm3 at 0 °C, volume coefficient of expansion 0.000054/C°) in an ideal air density of 1.2 mg/cm 3 Apparent mass corrections to any other basis can be furnished if requested.

(d) For periodic recalibrations of reference mass standards, the user need measure only differences between weights or groups of weights within a set and compare them with computed differences. As long as the agreement is within allowable limits, the values can be considered constant within the precision of the comparison process. Mass standards which are submitted to the Bureau for recalibration frequently are tested in this If these tests indicate that no significant changes have occurred, continuation report so stating and referring to the previous NBS Report of Calibration will be issued.

a

Item

Description

212.311z Calibration of reference mass standards

described in TN 288.

or supporting services

212.312 Reference standards of volumetric apparatus.

(a) The procedure used almost universally for testing glass volumetric apparatus is to weigh the amount of distilled water contained or delivered with reference to the graduations marked on the instrument, the volume being computed from the density of the water (for tables see NBS Circular 19, available on request). The quality of the markings and the exercised in reading or setting the liquid level are major factors in test calibration and usage. Normally the Bureau will accept instruments for calibration which have volumes in the range 1 mm. to 1 gallon and which conform essentially to requirements contained in NBS Circular 602, "Testing of Glass Volumetric Apparatus, "* Federal Procurement Specifications NNN-B00789 (Buret, straight, precision), NNN-F-00395a (Pipet, volumetric) NNNP-00350a (Pipet, measuring), or NNN-F-00289a (Flask, volumetric), if such instruments are to be used as reference or transfer standards.