Dimensional Metrology - Calibration Services

Ordering Calibrations Services

The Dimensional Metrology Program maintains the primary length standard, provides calibration facilities for length and related quantities, advises clients on instrumentation, testing procedures, and new developments in length metrology, and conducts research to develop new atomic wavelength standards for length metrology and other applications.

 National Standard of Length
 Facilities
 Limitations
 Uncertainties
 Calibration Services and Fees

Contact: Dr. Jim Pekelsky
Tel. (613) 993-7578

National Standard of Length

The metre is realized in accordance with the guidelines published by the Bureau International des Poids et Mesures (BIPM) (CCDM "mise en pratique", 1992), which specify the construction and operating conditions for sources of radiation at a variety of recommended wavelengths. The uncertainty for the published wavelengths depends on the source device and ranges from 6 x 10-12.

The Group maintains two 633-nm (visible red wavelength) helium-neon lasers stabilized on the 11-5 R(127) component of iodine-127, with an uncertainty of 5 x 10-11.

One of these lasers is designated as the National Standard of Length. The second laser possesses equivalent accuracy and is used in comparisons with the National Standard to monitor their long term frequency behaviour. The second laser system is also used as a transportable transfer standard for international comparisons.

Facilities

The dimensional metrology facilities are class-10,000 cleanrooms with the temperature maintained at 20.0 ± 0.1°C and relative humidity controlled to 40 ± 2%. A separate underground tape facility, also temperature-controlled to 20.0 ± 0.1°C, is equipped to measure tapes up to 50 m.

The Group calibrates 633-nm helium-neon reference lasers against the National Standard laser. These are then used in interferometers and comparators to measure the length of gauge blocks and other types of artifacts, thereby providing a calibration that is traceable to the National Standard of Length for each instrument and artifact used in the laboratory.

Limitations

Dimensional and related calibrations are performed at 20°C. The Group will undertake a calibration only if the artifact is in substantially new condition and is of a quality that warrants the requested work. 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 (CLAS).

Uncertainties

The uncertainties quoted in the descriptions below are expanded uncertainties representing a confidence level of approximately 95%. 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

Ordering Calibrations Services NEW procedures effective March 23, 2006.

 Laser/Wavelength Frequency
 End-Standards (Gauge Blocks & Length Bars)
 Precise Scales
 Level Rods & Target Bars
 Diameter & Roundness Standards
 Angle Standards
 Surface Roughness Standards
 General Form & Profile Measurements

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 INMS Frequency and Time Group.

End-Standards (Gauge Blocks and Length Bars)

(A33-04-02-01 to A33-04-02-70)

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 38 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 end-standard attendant processes such as unpacking, administration, instrument set-up, reporting, and repacking, plus the inspection and calibration of each type of gauge in the set.

Precise Scales

(A33-04-03-01 to A33-04-03-02)

The NRC Line-Standard Interferometer accepts precise scales up to 1 m long on metal or glass substrates having either dark lines on a highly reflective plane, such as metre bars formerly used to define the metre, or high-reflectance lines on a dark plane, such as microscope stage micrometers and moir‚ encoder scales. Calibration of the length of intervals between the lines is done by counting the number of reference optical wavelengths as the scale is traversed under a photoelectric line-detecting microscope. Calibration uncertainty is commensurate with the quality of the scales. The lowest uncertainty (not less than 20 nm) is achieved in the labour-intensive stationary-mode and is used only for the best scales. The scanning mode is more automated, but has a greater uncertainty (not less than 100 nm). The fee depends on the number of intervals to be calibrated.

Level Rods and Target Bars

(A33-04-05-01 to A33-04-05-02)

Three-metre level rods with scales on an invar ribbon, and 60-inch target bars for optical triangulation systems are calibrated using a long-bed Abbé comparator equipped with a laser interferometer. Under optimal conditions, these artifacts can be calibrated to an uncertainty commensurate with the quality of the gauge, but not less than 10 µm.

Diameter and Roundness Standards

(A33-04-06-10 to A33-04-06-40)

Diameters from 5 mm to 300 mm are measured on a Mitutoyo Legex 707 CMM using a gauge-block substitution technique. Smaller external diameters, down to 0.1 mm are measured on a 1-D mechanical comparator (SIP305M). The best-measurement capability uncertainty depends on the size and quality of the artifact:

External cylinders (plugs), 5 mm to 300 mm: U = [0.15 + 0.7D/1000] µm, D is diameter in millimetres

External cylinders (pins, wires), 0.1 mm to 5 mm: U = [0.25 + 0.01D] µm, D is diameter in millimetres

Internal cylinders (rings), 5 mm to 300 mm: U = [0.15 + 0.7D/1000] µm, D is diameter in millimetres

Balls, spheres, 5 mm to 250 mm: U = [0.15 + 0.7D/1000] µm, D is diameter in millimetres

Diameter of a cylinder is usually measured in the marked reference direction across the circle, taken at three elevations. Special diameter measurements are available, and additional work can be done at cost in order to reduce the quoted routine uncertainties. Roundness and sphericity of artifacts up to 350 mm in diameter and 406 mm in height are measured on a vertical-spindle rotating-stylus type instrument (TR73 HPR). Routine calibrations are offered for:

External cylinders (plugs), 5 mm to 350 mm diameter

Internal cylinders (rings), 5 mm to 300 mm diameter

Spheres and hemispheres, 5 mm to 250 mm diameter

with roundness variations not exceeding 400 mm. Best measurement capability uncertainty is U= [17 + 11R] nm, R is the roundness in micrometres. Roundness of cylinders is usually measured at 3 elevations (charged as separate traces). Special roundness measurements are available, and additional work can be done at cost in order to reduce the quoted routine uncertainties.

Fees for Diameter and/or Roundness Standard calibration are calculated by adding the fees for the specific aspect measurements requested (A33-04-05-3x series) to the base fee (A33-04-06-30).

Angle Standards

(A33-04-07-00 to A33-04-07-41)

The angle calibration facility uses an interferometric optical sine bar to generate angles over a 10 degree range to an uncertainty of 0.005 seconds. Combined with a 2-axis autocollimator and a precise indexing table, a variety of angle devices can be calibrated. These include: 1- and 2-axis autocollimators, angle gauge blocks, optical polygons, and index tables. Calibration uncertainty is commensurate with the quality of the angle standard, but not less than 0.1 seconds for routine calibrations.

Surface Roughness Standards

Measurements of surface roughness are made using stylus equipment (RTH Form Talysurf) and a wide range of surface-roughness parameters can be determined (Ra, Rq, Ry, Rz, etc.). The instrument resolution is 10 nm over a 6 mm range. Roughness patches, steps, or grooves can be measured to an uncertainty commensurate with the quality of the standard, but not less than 2% + 4 nm for any parameter.

General Form and Profile Measurements

General form (shape and size) within an envelope of 700 mm x 700 mm x 450 mm can be measured on the Group's high-precision coordinate measuring machine (Mitutoyo Legex 707 CMM) with a linear uncertainty commensurate with the quality and size of the standard, but not less than 0.5 µm, and volumetric uncertainty not less than 0.8 µm. Smaller profiles, up to 6 mm high x 120 mm long, can be measured using the RTH Form Talysurf Stylus-type profiling instrument. The measurement uncertainty is given by (5L) nm, where L is the length of the profile in millimetres, but is not less than 100 nm.