NEW CALIBRATION SERVICES AND RESEARCH ACTIVITIES SERVICES OF NMISA S LENGTH SECTION. O.A. Kruger, length section NMISA. Pretoria.

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1 NEW CALIBRATION SERVICES AND RESEARCH ACTIVITIES SERVICES OF NMISA S LENGTH SECTION O.A. Kruger, length section NMISA Pretoria 0001 oakruger@nmisa.org 1. Abstract Previously, a paper was presented on the new approach of the National Metrology Institute of South Africa (NMISA) Length section to the maintenance and dissemination of National Standards to industry. Proposed ways for NMISA to best serve industry requirements were discussed. In this paper; the progress to date, the implementation and the impact of these plans on the industry will be discussed. The following areas that will be covered: i) New services of the Length section ii) New equipment acquired iii) Research projects Projects within NMISA cutting across different disciplines and involves different laboratories to work towards a common goal to support industry, will be discussed. Three cross cutting projects have been identified, one of which is advance manufacturing. While there will be contributions from different laboratories within NMISA, this paper we will discuss the involvement of the Length section. SI Perspective NMISA is mandated to maintain the National Measurement Standards and its associated measurement systems and to dissemination traceability throughout the country. In the field of length and dimensional measurements, NMISA reproduce the SI definition of the metre and maintains a series of secondary standards that are used in the calibration of equipment submitted by industry. The National Measurement Standard for length in South Africa is the Iodine-Stabilised Helium Neon laser, stable to 2 parts in 10-11, as published in the Government Gazette. Stated uncertainties quoted, are based on a standard uncertainty multiplied by a coverage factor of k = 2, which, unless specifically stated otherwise, provides a level of confidence of approximately 95%. In the CMCs uncertainty statements, the notation Q[a; b] stands for the root-sum-square of the terms between brackets: Q[a, b] = a 2 + b 2 The uncertainties associated with accredited parameters are available on the SANAS website Uncertainties stated on the calibration certificates may differ from the uncertainties as per the schedule of accreditation, due to the following reasons: i) The quality of the Standard under Calibration. ii) The environment under which the calibrations were performed.

2 It is important to remember that the standard under calibration may be used under different conditions than when it was calibrated. The temperature, support conditions and differences in the measuring equipment will influence the readings and additional uncertainties will generally occur. All calibrations are carried out in an environment controlled to a temperature of 20 C ± 1º C and a relative humidity of 45 % ± 15 %, unless otherwise stated. Figure 1: Capabilities of laboratory illustrated with the range and the uncertainty. 2. Laser Calibrations The frequency of single-mode frequency-stabilised lasers is calibrated by referencing it to the iodinestabilised He-Ne laser. Measurements are made by a beat frequency comparison between the test and reference laser. With this technique, the beams from the reference and test laser are combined and focussed onto a detector. The resulting beat frequency signal is the difference in frequency between the two lasers. This calibration service is available for 633 nm (red) lasers. Laser interferometer displacement calibrations are done by direct comparison against a standard laser interferometer. Displacements of up to 10 metres are calibrated. Velocity of Light Compensation: The air temperature, pressure and humidity sensors of laser systems can be calibrated by the appropriate laboratories.

3 Figure 2; National Measurement Standard for length in South Africa, the iodine stabilised HeNe laser(winters system). 3. End Standards up to 300 mm (Gauge Blocks) NMISA accepts steel, tungsten carbide and ceramic gauge blocks for calibration which are classified as Grade 00, 0, Calibration or Reference grades. Gauge blocks of grades 1 and 2 or gauge block accessories are not accepted for calibration. NMISA is capable of calibrating both metric and imperial gauge blocks. A TESA Gauge Block Interferometer, which uses two lasers; red and green, is currently used for the calibration of gauge blocks. Each gauge is measured by wringing the measuring surface to a quartz base platen and determining the perpendicular distance from the base plate surface to the centre of the exposed face. The practical length is derived from the mean value of two measurements. The correction associated with the coefficient of thermal expansion will depend on the material of the gauge block. Figure 3; A steel gauge block wrung onto steel platen.

4 4. End Standards up to mm (Length Bars) NMISA is capable of calibrating both metric and imperial length bars and bars with rectangular, square or circular cross-sections are calibrated. Bars with nominal sizes between 100 mm and 1000 mm are calibrated on the Length Bar Measuring Machine using a Hewlett Packard laser measurement system, traceable to the National Measurement Standard of Length; the Iodine Stabilized He Ne Laser. The bar is supported in a horizontal position at the Airy points. Corrections are made for the variation of the laser wavelength with ambient atmospheric conditions and the length of the bar is corrected to 20 C. Figure 4; One metre length bar on length bar measuring machine. 5. External and Internal Diameter Standards External and Internal diameter standards are calibrated on a Pratt and Whitney Lab Master. Measurements are achieved by gauging probes that movies on a virtually frictionless air slide. The relative position of the probes is detected by a laser interferometer, gauge blocks are used as standards. Internal diameter standards are calibrated for diameter, and roundness. Diameters of nominal sizes between 5,0 mm and 250 mm are calibrated using the Pratt and Whitney Lab Master. External diameter standards in the form of discs, plugs or thread wire cylinders which may or may not be supported between centres are calibrated for diameter and roundness. Plug gauges of nominal sizes from 0,1 mm diameter up to 330 mm diameter can be calibrated. Thread wire cylinders are calibrated using the Wedge Comparator. Diameter standards are calibrated for roundness on the Talyrond 252.

5 Figure 5: Gauge block set up as standard on universal measuring machine. 6. Line Scales (Rules, Stage Micrometers, Surveying Tapes) Line scales in the form of stage micrometers as used in the calibration of eyepiece graticules, microscopes, precision linear scales, glass rules, steel rules, tapes and staffs are calibrated. The accuracy of scales calibrated depends on: i) The material and form of the scale. ii) The nature of the surface on which the lines are ruled. iii) The quality of the lines. For the highest accuracy precision scales, the SIP 214B is used. The instrument incorporates: i) A laser interferometer for the linear scale which supplies the traceability link. ii) An electronic microscope as the locking device on the individual lines. iii) A thermocouple for measuring the temperature of the line scale. Steel rules up to mm are calibrated against a laser interferometer, while supported on a flat surface. Precision surveying tapes and wires of up to 50 m are calibrated in catenary under a specified tension. The rate of change with tension of tapes or wires can also be calibrated. The tape material and the value for the tension weights must be submitted. For the tension weights the value of gravity is taken as 9,80665 m/s 2. Electronic Distance Meters (EDMs) are calibrated up to 50 m in the tape tunnel and against two base line positions, 50 metres and 500 metres. The base line positions are calibrated with differential GPS.

6 Figure 6: 50 metre tape tunnel used for tapes, EDMs and rules. 7. Optical Flats and Optical Parallels Optical flats and parallels are used to calibrate the flatness and parallelism of measuring anvils. The optical flats and parallels are measured with a Zygo GPI interferometer, using a He-Ne laser light source; wavelength 632 nm. The master optical flat is calibrated using the three flat method where three optical flats are calibrated against each other, two at a time. The absolute flatness of each flat is calculated using the separation of errors technique. Optical parallels are calibrated for both flatness and parallelism on the Zygo interferometer. Mirrors can also be calibrated for flatness, as well as 90 prisms (penta prisms) and corner cubes for which an individual uncertainty is calculated. 8. Roundness Standards Roundness standards and magnification standards are calibrated for roundness using the Talyrond 73 or the Talyrond 252. Hemispheres are calibrated on the Talyrond 73 using the error separation technique where the hemisphere is measured and then moved through a specified angle (30 ) and remeasured. This is repeated till a full circle is completed, resulting in 144 readings. These readings are entered into a matrix which separates the errors of the hemisphere from the spindle errors. Magnification standards are calibrated on the Talyrond 252.

7 Figure 7: A glass hemisphere is calibrated on the Talyrond Surface Texture Standards Surface texture and step height standards are calibrated on a Form Talysurf Series 2 measuring machine. The Form Talysurf is calibrated using a calibration ball of 22 mm in diameter. The Talysurf has a resolution of a low 0,2 nm over the full range of 10 mm. Parameters required for the surface texture calibration must be clearly specified during contract review, currently the laboratory is only accredited for Ra and Rt parameters. The Form Talysurf can also measure radii and angle on small surfaces, for example moulds and dies. The surface texture on curved objects can also be measured. Figure 8; Form Talysurf with 10 mm travel in z axis down to 0,2 nm resolution and 120 mm travel in x axis. 10. Angle Standards All angle calibrations are performed using a Moore Index Table interferometer. NMISA has 2 index tables, one with 1440 teeth and the other This allows a movement of the tables at 15 minute and 10 minute intervals respectively. If used in combination it can be moved at 5 minute intervals.

8 The tables are calibrated by using the error separation technique similar to the method used for the calibration of the roundness standards. Autocollimators are calibrated on a small angle generator which incorporates a laser interferometer. A phase shifting flatness interferometer in place of the autocollimator is used in special applications. The interferometer has very good repeatability and overall accuracy, compared to the autocollimator. The calibration of levels is also performed on a small angle generator against a laser interferometer 11. Co-Ordinate Metrology Global Image CMM The DEA Global Image CMM has a measuring volume of 2000 mm x 900 mm x 800 mm and is fitted with a Renishaw PH10MQ indexable probe head. It has two probing systems, a TP200 touch trigger probe and a SP600M continuous scanning probe. The CMM is equipped with applicable stylus changers for use with the probing systems. Each of the three measuring scales (X, Y, Z) of the CMM is equipped with a temperature sensor, which record the temperature during measurement together with a part temperature sensor which enable the software/machine controller to perform temperature compensation. The coefficient of thermal expansion (CTE) for the machine scales are 10,5 x 10-6 / C. The CMM is mainly used for the evaluation of manufactured components according to specified tolerances as well as to provide the required data for reverse engineering purposes. Accuracy Specifications MPEE = ± (1,9 + 3L) µm MPEP = ± 1,9 µm Uncertainties of measurement Linear measurements = ± (2,4 + 3L) µm GD&T measurements = ± 2,4 µm

9 Figure 9; DEA Global Image CMM Micro-CMM The micro-cmm has a measuring volume of 245 mm x 200 mm x 175 mm and a two probing systems, a Renishaw TP200 touch trigger probe and a UMAP103 fibre optic touch probe with a diameter of 35 μm and a vision/camera system for non-contact measurement. The measurement software used is MCOSMOS for contact measurements and VISIONPAK for non-contacting measurements. The μcmm is used to measure various micro-parts and for the calibration of standards, for example: hardness indenters, acoustic microphones and optical apertures. Accuracy Specification MPEE (TP200) = ± (2,0 + 3L) µm MPEP = ± 1,9 µm MPEE (Vision) = ± (0,8 + 2L) µm UMAP103REP = ± 0,1 µm Figure 10; UMAP Micro-CMM Zeiss Prismo Ultra CMM The Zeiss Prismo Ultra CMM is the latest addition to NMISA and is the first CMM of its class in Africa. The CMM has a measuring volume of 1300 mm x 900 mm x 700 mm and is fitted with a VAST Gold probe head. The VAST Gold probe head can perform point-to-point measurements as well as for 3D scanning. The probe head is equipped with an integrated navigation system to automatically determine the optimum scan speed and point density during the scanning of GD&T measurements. The CMM is equipped with a stylus changer for use with the available stylus systems. The measurement scales of the three axis (X, Y, Z) are manufactured of Zerodur with a CTE of 0,01 x 10-6 / C. Temperature sensors record the part temperature during measurement which enables the

10 software to perform temperature compensation. The measurement software used is Calypso for general measurements and scanning. Gear-Po software is used for the inspection of gears and calibration of master gears. AFM Gauge-Check software is used for comparative calibrations of length standards and diameter standards. This high accuracy CMM is mainly used for the calibration of step gauges, length bars, ring and plug gauges, squares, involute gears and master parts. Accuracy Specification MPEE = ± (0,55 + L/500) µm MPEP = ± 0,55 µm Uncertainties of measurement Step Gauge calibration = ± (0,3 + 1 x 10-6 x L) µm Ring/Plug gauge calibrations = ± 0,4 µm GD&T measurements = ± 0,55 µm Figure 11; Zeiss Prismo Ultra CMM 12. Research Projects To stay on-par of new developments and to support the local industry, NMISA continually invest in research. The research areas that the Length section currently focussed on are: i) New optical frequency standards, the continued development of the National Measurement Standard of length. Not just to improve on its the current services, but to provide for new frequencies (wavelengths) measurements. ii) Refractometer for the measurement of the refractive index of air, used in all laser measurements to determine the velocity of light (V.O.L) compensation.

11 iii) Upgrade of the high accurate roundness machine for defining a National Measurement Standard of roundness measurements. Together with this, a new secondary roundness machine will be procured. iv) Upgrade of the surface texture measuring machine to improve its range and resolution. The upgrade of the software will enable NMISA to perform 3D measurements. v) Double ended interferometer to improve our calibration capabilities of gauge block and length bars. vi) Support to the manufacturing industry: Various projects e.g.; additive manufacturing (3D printing), thin film thickness measurements. New laser tracker. Figure 12; Leica laser tracker CMM vii) Dimensional measurements for Nano-metrology, a new Atomic force microscope (AFM) was installed and will be used for the measurements of standards to provide traceability for nanometrology

12 Figure 13; Nanosurf Flex AFM