We are well equipped to perform many types of measurement of length, angle and related quantities, and our facilities are also available for appropriate scientific and industrial measurement applications:
laser wavelength standards and laser interferometers end standards (gauge blocks, length bars, height setting micrometers, step gauges, pitch reference screws, rigid linear scales, stage micrometers, surveying tapes) coordinate measuring machine electronic distance measuring instruments angle standards (combination angle gauges, precision polygons) measuring tools (optical flats, optical parallels) diameter standards (external cylindrical standards, cylindrical ring standards, roller gauges, steel ball gauges) roundness surface roughness machine tools dimensional measuring instruments and measuring machines nanoparticle size measurements
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Before consigning an instrument for calibration always consult us to discuss your requirements. For further information contact calibration.coordinator@measurement.gov.au.
Note on reporting results
Temperature effects influence the accuracy of measurements and considerable care is taken to reduce these effects to negligible levels wherever possible, or to make appropriate corrections where necessary. Unless otherwise requested the results of measurement are normally referred to a standard temperature of 20°C.
In many length measurements the method adopted may require the application of a small compressive force. Corrections for this compression are applied where necessary and, unless otherwise stated, all quoted results are referred to zero applied force.
The uncertainty values that are quoted in a report normally correspond with internationally accepted values for the class of measurement. Achievement of this level of uncertainty depends on a number of factors including the precision of the geometry and the finish of the surfaces of the test item. For example, in the case of an angle gauge, the quoted uncertainty in the departure of the angle from its nominal value will be greater than normal if there are excessive departures from flatness of the measuring faces or from squareness of those faces to the side faces. When necessary, the appropriate uncertainty requirements for a calibration should be discussed with NMI staff.
The vacuum wavelength of a laser may be determined by frequency comparison against NMI's primary standard lasers. At present this facility is limited to 633 nm, 612 nm and 543 nm helium-neon lasers.
A performance test can be carried out on laser length measuring interferometers. It includes examination of the environmental compensation units.
Gauge blocks are rectangular blocks usually ranging in length from 0.5 mm to 1 m, that have very flat, parallel faces. The length of these blocks can be measured either by interferometry or by comparison with NMI standard gauge blocks depending on the accuracy required. Reports giving the departure from nominal size of each gauge block are issued, along with the associated uncertainties.
With interferometry the gauge blocks length can be measured to an accuracy that is of the order of 40 nm for blocks that are 100 mm long.
Typical uncertainties for comparison are given below.
Bars of square and circular cross-sections that are up to 1 000 mm in length can be calibrated by direct comparison with NMI's standard bars as follows:
A more accurate interferometric measurement can be performed on suitable bars that have lengths up to 1 000 mm.
Height setting micrometers used as reference standards of length for work performed on a surface plate are examined for accuracy of the measuring faces and of the micrometer. Accessory riser blocks are also examined.
Step gauges are used as reference standards for the calibration of coordinate measuring machines (CMMs) and machine tool scales. Step gauges up to 750 mm long are calibrated on NMI's CMM using an integrated laser interferometer measurement system.
Pitch reference screws used as reference standards for measuring the errors of screw-pitch-measuring machines are examined for departures from nominal pitch along the marked generator.
NMI examines rigid linear scales up to 1 m in length. The accuracy with which an interval on such a scale can be determined depends on many factors, among which are the material and form of the scale, the nature of the surface on which the lines are ruled, and the quality of the lines. Two classes of accuracy are offered for measurements of one or more intervals:
A typical calibration usually involves measurements of up to 30 intervals in the following manner:
Measurement of the length of an interval is carried out at a temperature close to 20°C. The coefficient of thermal expansion of the material of the scale must be known with sufficient accuracy to enable the observations to be corrected to standard temperature. The results of the calibration as quoted in the report apply at the mean temperature during the observations.
NMI examines stage micrometers used as reference standards in the calibration of eyepiece graticules and of micrometer eyepieces.
An 80 m tape tunnel is available to calibrate surveyors tapes and laser interferometers.
NMI examines precision surveying tapes in respect of one or more of the following features:
The maximum width of cross-section of a tape that can be calibrated is 9.5 mm.
In general, two classes of test are offered for the determination of length:
For Invar tapes a knowledge of the coefficient of expansion is required to an accuracy commensurate with the class of test. When no specific information is supplied with the tape submitted for calibration a coefficient of +1 x 10-6 per °C is assumed. For steel tapes the coefficient of expansion is assumed to be +11 x 10-6 per °C.
Unless otherwise requested, the length of a tape is given for a temperature of 20°C and at the standard value of gravity, 9.80665 m/s².
NMI's high accuracy CMM is equipped with comprehensive measurement and evaluation software and can measure a wide range of reference standard artefacts and components within its 800 mm x 600 mm x 600 mm volume. It is suited especially to complex evaluations and to measurements requiring low uncertainties. Examples include the measurement of ballplates, dies, gears, height-setting micrometers and high accuracy proof components.
In addition, NMI has an industrial accuracy CMM with an indexing head, scanning probe and a measuring volume of 1200 mm x 900 mm x 800 mm. This machine is available for the measurement of larger components and for the provision of training to CMM operators.
Facilities are available to input coordinate data (e.g. CAD/CAM) and to output measurement results using IBM PC compatible floppy disks.
Advice and consultation on CMM performance and applications can be provided. NMI actively collaborates with the CMM Group, a technical group for users, potential users and suppliers of CMMs, and provides a nation-wide coordinate measurement assurance program (COMAP) using a number of calibrated artefacts comprising stepgauges and ballplates.
NMI maintains a 650 m EDM baseline, consisting of seven pillars, which is traceable to the national standard of length. Procedures have been developed for the verification of precision EDM instruments on the baseline. As an alternative the baseline can be made available to approved surveyors for functional checks or for instrument verification.
A second alternative is to provide traceability of the EDM oscillator to the national standard of frequency. Simple functional tests are also offered.
NMI maintains a pair of precision, photoelectric autocollimators having a minimum resolution of 0.01 seconds of arc. The autocollimators are calibrated using a special sine table and are traceable to the national standard of length. The autocollimators are used in conjunction with a pair of precision indexing tables having a minimum increment size of 0.25 degrees. The indexing tables are cross calibrated against each other using the photoelectric autocollimators and the self defining property that there is exactly 360 degrees in one full circle.
Sets of combination angle gauges are examined for flatness of the measuring and side faces, squareness of the measuring faces to the side faces, and departure of the angles from their nominal values. The uncertainty of these measurements is typically 0.3 seconds of arc.
Precision polygons in the form of hardened steel or glass polygonal blocks having a number of equally inclined faces are examined for flatness of the measuring faces and the support face, squareness of the measuring faces to the support face, and the departure of each angle from its nominal value. The uncertainty of these measurements is typically 0.2 seconds of arc.
Facilities for the examination of most precise measuring tools are available at a number of NATA-accredited laboratories. NMI does not normally examine measuring tools apart from optical flats and optical parallels. In special circumstances we examine surface plates (particularly large plates requiring on-site examination) and toolmakers flats.
Each application for examination of an optical flat must give full particulars of the flat to be tested, including the material of which it is made, its approximate physical dimensions, the maximum acceptable departures from flatness of the working surface and the intended method of use. The uncertainty of flatness measurement is typically 0.05 µm.
Optical parallels for checking the flatness and parallelism of the measuring faces of external micrometers are examined in respect of the flatness and parallelism of the working surfaces and the overall length of each parallel. Measurement uncertainties are typically 0.05 µm for flatness, 0.03 µm for parallelism and 0.10 µm for length.
Standards in the form of discs, plugs or cylindrically ended bars, which may be supported between centres and are intended for use with screw-diameter measuring machines, are examined for mean diameter and variation in diameter. Concentricity of the gauging surface with the axis of the centres is also determined in the case of standards up to 50 mm in diameter. For cylindrical standards up to 150 mm in diameter, the uncertainty in the measured diameter is typically 0.4 µm while the uncertainty on roundness is typically 0.05 µm.
Cylindrical ring standards in the form of plain setting rings used as reference standards with internal-diameter-measuring machines are examined for conformity with AS 1001 Plain Setting Rings for Internal Measuring Equipment, Metric Series. The uncertainty of a single measured diameter is typically 0.2 µm and that of the roundness measurement is typically 0.05 µm.
Hardened steel rollers for use as reference standards are examined for diameter, departures from cylindrical form, flatness of the end faces and length. For roller gauges up to 30 mm in diameter, the uncertainty in the reported diameter is typically 0.5 µm, while for roundness the uncertainty is 0.05 µm.
Hardened steel ball gauges for use as reference standards are examined for diameter and departures from spherical form. The uncertainty in diameter is typically 0.2 µm and that in roundness is typically 0.05 µm.
Measurement of roundness is made using rotating spindle stylus equipment. Roundness standards such as hemispheres, magnification standards and inclined standards can be calibrated. The roundness and sphericity of precision parts and components can also be measured.
Measurements of surface roughness uses stylus equipment in accordance with the principles set out in international and Australian standards. A wide range of surface-roughness parameters can be determined and these include arithmetic-mean deviation, root-mean-square deviation, maximum peak-to-valley roughness height, and ten-point height. In particular we calibrate surface-roughness standards, grooves and steps used to determine the magnification of static-displacement-measuring instruments. Advice on problems related to surface roughness and its measurement can also be provided.
Facilities for the examination of most types of machine tools are available at a number of NATA-accredited laboratories. NMI advises on problems relating to the examination of machine tools, on measurement techniques, and on appropriate measuring equipment. In special circumstances the examination of a machine tool may be undertaken.
A wide variety of dimensional measuring instruments and measuring machines require regular calibration as part of their normal operation and maintenance. Advice on calibration methods and problems arising in calibration is available and in special circumstances calibrations are undertaken.
NMI offers a service for calibrating standard reference powders and nanoparticles down to 1 nm, using a high-level dynamic light scattering instrument.