Dimensional metrology

Traceability to the SI unit of length: the metre

The metre is realized in accordance with its definition: "The metre is the length of the path travelled by light in a vacuum during a time interval of 1/299 792 458 of a second." In practice, length is measured in terms of the wavelength of light from a laser that is highly stabilized in its output frequency. The wavelengths of lasers that are used by the NRC for dimensional calibrations are calibrated by comparing them to optical frequency/wavelength standards maintained by the NRC. These standards include an ensemble of three helium-neon lasers that are stabilized on a transition component of the 11-5 band, R (127) line of iodine-127, with a relative expanded uncertainty (2s) of 4.2 x 10-11. They are used to calibrate the optical frequency/wavelength of helium-neon lasers in the red at 633 nm, which are widely used in precision interferometric dimensional metrology. Their accuracy is guaranteed through periodic comparisons with each other and through direct calibration, with traceability to the SI second and SI metre, provided by means of an optical frequency comb that is maintained by the NRC. Lasers at other wavelengths that are used by the NRC are calibrated directly by means of the optical frequency comb.

Facilities

The dimensional metrology facilities are temperature-controlled clean rooms maintained at 20.00 °C ± 0.05 °C with relative humidity controlled to 40 ± 2 percent.

Limitations

Dimensional and related calibrations are performed at 20 °C. The artifact must be in substantially new condition and of a quality that warrants the requested calibration. The acceptable accuracy-grade for a specific artifact can usually be judged from the uncertainty of the measurements described below; lower-grade artifacts and measuring instruments such as micrometers and vernier calipers should be referred to secondary laboratories accredited under the Calibration Laboratory Assessment Service.

Uncertainties

The uncertainties quoted in the descriptions below are expanded uncertainties representing a confidence level of approximately 95 percent. They were obtained assuming a normal distribution and multiplying the standard uncertainty (one standard deviation) by a coverage factor of k = 2.

Calibration services and fees

If you wish to order a calibration service, please request a quote from the following technical contact:

Dr. Brian Eves
Telephone: 613-991-3279
EmailBrian.Eves@nrc-cnrc.gc.ca

Note that the calibration costs quoted DO NOT include shipping, insurance or the cost of a customs broker. The client must arrange and pay for these services separately.

Calibration number Description Fee
A33-04-00-00 Custom dimensional metrology services Fee on request
A33-04-00-01 Handling fee, for processing items found not suitable for calibration. A charge is levied for any instrument or standard found to be unsuitable for calibration. This fee covers opening, inspection and return, and is based on the work done prior to discovery of the fault. $250
A33-04-00-02 Some items require special jigs and set-ups to adapt to existing calibration facilities and the client may be asked to pay for all or a portion of the cost. Fee on request

Laser wavelength/frequency

The frequency and vacuum wavelength are routinely determined for helium-neon lasers stabilized at a vacuum wavelength of 633 nm and 543 nm. Calibrations at other vacuum wavelengths may be possible by special arrangement.

Laser wavelength and frequency calibrations are carried out by the NRC metrologists. Please see the "Optical frequency" calibration services for more information.

End-standards (gauge blocks and length bars)

The NRC end-standard interferometer accepts end standards made from any suitable material, such as steel, carbides, and ceramics. Interferometric length calibrations are done using the method of exact fractions and three or more wavelengths from at least two radiation sources. Only the best grades of blocks are admitted for interferometric measurements. Gauges are first inspected to ensure that the end surfaces are flat, parallel, and will wring to a reference optical flat. Gauge blocks up to 100 mm are calibrated in a vertical orientation, wrung to an optical flat. Up to 18 gauge blocks can be loaded into the instrument at a time. Long bars over 100 mm and up to 1 m are calibrated one at a time in a horizontal orientation, supported at their airy points and with a small optical flat wrung to one end. Calibration uncertainty is commensurate with the quality of the gauges and under optimal conditions is limited to (20 + 300L) nm, where L is the length of the gauge in metres. Steel gauges are demagnetized and given a rust-preventative coating prior to being returned.

Short rectangular gauge blocks (between 1 mm and 100 mm) are the easiest to calibrate. Thin gauges (less than 1 mm) and hoke-type (square section) gauges are more difficult to inspect and measure.

Calibration of a set of one or more gauges consists of the preparation (unpacking, administration, instrument set-up and repacking) for which the handling fee applies, plus the inspection and calibration of each type of gauge in the set.

Research publications:

Calibration number Description Fee
A33-04-02-01 Handling & setup fee $500
A33-04-02-31 Calibrate a short (< 100mm) gauge block $220
A33-04-02-35 Calibrate a length bar (> 100mm, up to 1000mm) $725
A33-04-02-41 Calibrate a set of 112 short gauge blocks $23,145
A33-04-02-42 Calibrate a set of 88 short gauge blocks $18,335
A33-04-02-52 Calibrate a set of 81 short gauge blocks $16,820
A33-04-02-55 Calibrate a set of 9 short gauge blocks $2,270
A33-04-02-61 Calibrate a set of 8 length bars $6,120

Contact

Dr. Brian Eves
Telephone: 613-991-3279
EmailBrian.Eves@nrc-cnrc.gc.ca

Business OfficeMSS-SMEBusiness-Affaires@nrc-cnrc.gc.ca