that a weight meet the adjustment tolerances established for Classes A, B M, or S-1 (as described in Circulars 3 and 547, Volume III, of NBS Handbook 77*) prior to submission. Normally weights are available from manufacturers, many of whom can furnish directly documentation suitable for meeting quality assurance contracts and requirements. (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 to 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. (c) The values of true mass (and an apparent mass correction) included in the report will be determined by using computed volumes based on 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 density values. values. The apparent mass corrections are computed for 20 °C with reference Normal Brass (density 8.4 g/cm3 3 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 manner. If these tests indicate that no significant changes have occurred, a continuation report so stating and referring to the previous NBS Report of Calibration will be issued. 212.311z Calibration of reference mass standards or supporting services described in TN 288. 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. or quality control will be accepted for test. Values will be furnished in letter report. the (2) Suggested test procedures for the verification of ompliance of precision grade glassware with specifications and tolerances re available on request. (b) The usual calibration procedure for metal volumetric pparatus consists of determining the value "to contain" or "to deliver" by ither gravimetric means or by the use of transfer standards. Normally the ureau will accept instruments for calibration which have values in the ange 1 gill to 1,000 gallons, which comply essentially with the specificaions contained in NBS Monograph 62, "Testing of Volumetric Standards, nd which are free from dents, bumps, or scratches. (1) While it is preferred that the zero index or the gage cale be adjusted and scaled prior to calibration, these operations can be ncorporated into the calibration procedure if requested. Slicker ype standards should be adjusted by the manufacturer. plate Item Description 12.312z Calibration of reference standard volumetric apparatus. 212.313 Density determinations of liquids and solids. (a) The usual procedure for determining the density of solids is ydrostatic weighing. At the Bureau liquid densities usually are deermined by gravimetric methods. The picnometer can be filled at a pecified temperature between 0 and 70 °C. Other methods are available epending on the requirements. The Bureau will accept requests for density eterminations if the need is critical, as in the support of scientific tudies or standard sample programs. Limitations on the mass, physical imensions, or volume of the sample are available on request. (b) Specific gravity hydrometers covering the range 0.62 to 3 nd proof spirit hydrometers in the range 0 to 200 proof, which are esignated reference standard hydrometers (used to test other hydrometers), ormally are accepted for calibration. A limited number of other types of eference standard hydrometers will be accepted for multipoint calibration ubject to a discussion of detailed requests. Instruments accepted must omply essentially with the requirements of NBS Circular 555, "Testing of ydrometers."* 2.313z Density determination of liquids or solids or the calibration of reference standard hydrometers. vailable from Superintendent of Documents, U.S. Government Printing fice, Washington, DC 20402. Acoustic Measurements 213.010 General. for the attention (a) Direct inquiries to, and mark shipments of: Sound Section, FW - 222, National Bureau of Standards, Washington, DC 20234. Telephone: 202-EM 2-4040-7083. (b) Fees for the regular services described in these schedules are listed in Part 8 of this publication. Fees for z items and other services have not been fixed and charges will be made for actual costs incurred. Upon request, estimates will be furnished for specific tasks which should provide a close approximation of actual cost. 213.011 Microphones. (a) Pressure calibrations are performed only on type-L microphones satisfying the requirements of USA Standards Institute Publication S1.12.1967, Specifications for Laboratory. Standard Microphones. In addition, microphones must be suitable for use with the calibrating couplers shown in Figures 6 and 10 of Publication S1.10-1966, Calibration of Microphones. Copies of these Standards can be purchased from the Institute at 10 East 40th Street, New York, New York 10016. (b) Pressure calibrations are reported in terms of open-circuit voltage per sound pressure applied uniformly to the diaphragm. The open-circuit voltage at the electrical terminals of a microphone depends on the stray capacitance connected across these terminals. The stray capacitance is defined by the geometrical configuration of the ground shield shown in Figures 6 and 13 of S1.10. If the ground shield dimensions not adhered to in making use of the response levels reported by the Bureau, errors may result. Methods for the measurement of open-circuit voltage are described in Clause 2.1 and in Figures 1 and 7 of S1.10. are (c) The free-field response levels of Western Electric Company Type 640AA condenser microphones, or equivalent, can be computed with good accuracy from the pressure response levels reported by the Bureau, using Table Al of S1. 10, provided the microphone is mounted on a preamplifier of size and shape illustrated in Figure 12 of S1.10. However, the use of manufacturers' response levels in conjunction with Table Al might result in errors unless the manufacturer has measured pressure response levels in accordance with S1.10. or (d) Associated preamplifiers power supplies should not be forwarded to the Bureau. The response levels reported are independent of the electronic equipment used in the test. Item 213.011a Description Pressure calibration of Western Electric Co. Type 640AA condenser microphone or equivalent from 50 to 10,000 Hz at discrete frequencies. Response given in terms of open-circuit voltage per unit sound pressure applied to the microphone. 11b discrete Pressure calibration of Western Electric Co. Type 640AA condenser microphone or equivalent from 50 to 20,000 Hz at frequencies. Response given in terms of open-circuit voltage per unit sound pressure applied to the microphone. 11z Special measurements not covered by this schedule. em 012 a 012b 012z 213.012 Hearing equipment. Description Calibration of earphones; applied voltage response as prescribed in the American Standards Association Specification Z24.9-1949, at not more than 20 frequencies between 100 and 10,000 Hz. Calibration of pure tone audiometers for screening purposes at nine fixed frequencies. Special measurements not covered by this schedule. 013a 013b Sound absorption coefficient, obtained by reverberation room 500, 1,000, 2,000, and 4,000 Hz. In case of tests on acoustical plasters or paintability tests, any construction work or painting done by the Bureau will be charged to the sponsor in addition to the fee listed. Sound absorption coefficient by impedance tube method at 500 Hz in the laboratory on acoustical tiles. 013z Special measurements not covered by this schedule. Engineering Mechanics 213.040 General. Direct inquiries to, and mark shipments for the attention of: neering Mechanics Section, ington, DC 20234. Telephone: EM 219, National Bureau of Standards, 301-921-2621. Item 213.041a Description Determination of Brinell number of a block to be used for calibration purposes, 5 separate indentations on each specimen. 213.042 Load cells with remote-reading electrical indicators. (a) Individual load cells or load cell systems must be accompanied by readout or indicating equipment and all associated cables and fixtures. (b) For the fee quoted, calibration will be made on one machine with up to 10 incremental loads applied consecutively without without return to zero load. For each load in excess of 10, an additional fee equal to onetenth of the applicable fee will be charged. For any device requiring the use of more than one machine, a charge will be made covering the cost of the additional work involved. (c) When devices submitted are found to be unsuitable for test or unreliable, the test may be discontinued and a charge will be made to cover the cost of the work done. Capacity exceeding 112,000 pounds but not exceeding 300,000 pounds: 213.042g Compression. 213.042h Tension. 213.0421 Tension and compression. |