TR CRITERIA FOR LABORATORY ACCREDITATION IN THE FIELD OF DIMENSIONAL METROLOGY

Transcription

1 CRITERIA FOR LABORATORY ACCREDITATION IN THE FIELD OF DIMENSIONAL METROLOGY Approved By: Chief Executive Officer: Ron Josias Executive: Accreditation: Mpho Phaloane Revised By: Specialist Technical Committee Date of Approval: Date of Implementation: SANAS Page 1 of 15

2 CONTENTS: 1. Purpose and Scope Definitions and References Environmental Requirements Measurements to be made Parameters Guidelines on Determining the Suitability for Calibration of Instruments or Gauges with Particular Reference to the Issuing of SANAS Certificates... 9 APPENDIX 1: Schedule of Accreditation ADDENDUM 1. Amendment record SANAS Page 2 of 15

3 1. Purpose and Scope The purpose of this document is to define the specific technical requirements to be met by accredited laboratories in the field of Dimensional metrology. This document is applicable to South African National Accreditation System (SANAS) Accredited Laboratories in this field. This document is applicable to accredited bodies undertaking this work and as defined in the Accreditation Act, Act No. 19 of Definitions and References SANAS PM SANAS Policy Manual SANAS A01 References, Acronyms and Definitions Accreditation Act Accreditation for Conformity Assessment, Calibration and Good Laboratory Practice Act, Act No. 19 of Environmental Requirements 3.1 An accredited laboratory working in the field of Dimensional measurements shall operate under the following conditions: The laboratory should be maintained at a temperature of 20 C ± 1 C and relative humidity of 40% to 60%. Where measurements are performed outside these specified requirements, the laboratory must produce documented evidence that it has made measurements under extreme conditions outside the prescribed requirements to determine that the measurement results are not invalidated. Should the results be adversely affected, the evidence must be produced to indicate that these influences are considered in the uncertainty budgets. This should be recorded on the certificates The reported measurements must be referred to the standard/reference temperature of 20 C and be recorded on the certificates Rates of change and gradients of temperature must be kept low. Localised control, using air or oil baths is permissible A high degree of cleanliness shall be maintained and adequate lighting shall be provided The laboratory shall be sited away from such sources of mechanical vibration, shock, and electrical and radio interference, as this would affect the accuracy of measurement. 3.2 It may not be possible for a laboratory to produce extreme conditions at will to do the necessary calibration measurements. It can thus be accepted if a laboratory produces evidence that it has commenced such calibration measurements at a specific date, and will continue to record such results over a period of one year to have a full cycle of climatic effects on the laboratory environment. In the interim, it will still be required that the laboratory allow for the unknown component of the effects on the measurement results in the uncertainty of measurement calculations. 3.3 In the event that the coefficient of expansion is unknown, then the laboratory is to quote the values recommended by the National Mertology Institute of South Africa (NMISA): Steel: 11,5 µm per meter per 1 C Tungsten Carbide: 4,23 µm per meter per 1 C SANAS Page 3 of 15

4 4. Measurements to be made Note: All the parameters defined must appear on the certificate. If not measured a statement must be made to that effect with the reason for non-measurement. 4.1 First calibration The first time a gauge or instrument is calibrated, if it is required, after discussions with the customer, that not all the parameters listed in this document be measured or checked the SANAS certificates issued must include statements concerning each, and a disclaimer regarding suitability for use. For example, if length bars were measured for length only then the certificate must, in addition to the length result, include a statement such as: Plus Parallelism Squareness Straightness Flatness - Not measured - Not measured - Not measured - Not measured This calibration was done to users requirements and does not verify the suitability of the equipment for its designed purpose. or 4.2 Subsequent calibrations "This calibration was done to users requirements and does not guarantee fitness for purpose" It is not necessary to repeat all measurements or checks on all the parameters listed in this document when gauges are re-calibrated. The customer should be consulted to determine what measurements or checks he requires. lf information, e.g. a previous calibration certificate is not available, it must be assumed that 4.1 applies. 5. Parameters MEASURED QUANTITY, INSTRUMENT OR GAUGE GAUGE BLOCKS LENGTH BARS OPTICAL PARALLELS OPTICAL FLATS PARAMETERS THAT MUST BE MEASURED OR CHECKED 1. Parallelism 2. Length 3. Flatness 1. Parallelism 2. Squareness 3. Straightness 4. Length 5. Flatness 1. Length 2. Parallelism 3. Flatness 1. Flatness SANAS Page 4 of 15

5 POLYGONS 1. Squareness of base to face 2. Angular error of facets 3. Flatness MICROMETER SETTING PIECES: A) FLAT ENDED 1. Parallelism 2. Gauge length 3. Flatness B) ROUND ENDED 1. Gauge length THREAD MEASURING CYLINDERS MICROMETER HEADS BENCH MICROMETER AND MICROMETER HEAD HEIGHT SETTING MICROMETER RISER BLOCKS DIAL INDICATORS PLUNGER TYPE DIAL INDICATORS LEVER TYPE SINE BARS & SINE TABLES SURFACE PLATES & TABLES (CAST IRON or GRANITE) ENGINEERS SQUARES 1. Actual diameter of individual wire 2. Uniformity of diameter 1. Squareness of measuring face to spindle axis 2. Error over one revolution 3. Periodic error over full travel 4. Flatness 1. Micrometer screw error 2. Parallelism of faces 3. Measuring force of fiducial indicator 4. Error over one revolution 5. Flatness 1. Squareness to spindle base 2. Distance between measuring face (individual and cumulative) 3. Error over one revolution 4. lndexing error check on micrometer drum 1. Co-planarity of support pads 2. Parallelism of support pads 3. Mean height of riser blocks 1. Repeatability of reading 2. Hysteresis (as per spec.) 3. Discrimination 4. Maximum error in reading (as per spec.) ln Going and Out Going 1. Repeatability and hysteresis of readings (counter-clockwise and clockwise) 2. Discrimination (counter-clockwise and clockwise) 3. Maximum error of (counter-clockwise and clockwise) 1. Flatness of all faces 2. Squareness of sides to measuring faces 3. Parallelism of measuring faces to axis of rollers 4. Parallelism of axis of rollers 5. Centre distance between rollers 1. Flatness 1. Straightness of blade edges 2. Parallelism of blade edges and stock edges 3. Flatness of working faces of stock 4.Squareness of blade edges to working faces of stock SANAS Page 5 of 15

6 SCREW PLUG GAUGES METRIC TYPE GO AND NO-GO SCREW PLUG GAUGES UNIFIED AND WHITWORTH SCREW RING GAUGES REFERENCE DISCS 1. Major diameter 2. Simple eflective diameter 3. Form of dearance 4. Thread profile 5. Pitch 6. Flank angle 1. Major diameter 2. Minor diameter (Go only) 3. Simple eflective diameter 4. Eflective diameter equivalent of pitch and angle error 5. Thread form 1. Minor diameter 2. Simple eflective diameter 3. Form of dearance and thread profile 4. Pitch 5. Flank angles 6. Or by means of calibrated check plugs 1. Diameter measured over the centre half of the gauge (lead, centre, trail - 0 & 90 o ) 2. Roundness PLAIN RING 1. Diameter (lead, centre, trail - 0 & 90 o ) GAUGES 2. Roundness PLAIN PLUG GAUGES 1. Diameter (lead, centre, trail - 0 & 90 o ) 2. Roundness CYLINDRICAL TAPER GAUGES TAPER RING GAUGES CYLINDRICAL SQUARES SOLID AND OPEN BLOCK SQUARES RIGHT ANGLE AND BOX ANGLE PLATES SCALES AND LINE STANDARDS 1. Diameter at datum point 2. Angle of taper 3. Length 4. Roundness 5. Straightness of taper 6. Datum step (where applicable) 1. Diameter at datum point 2. Angle of taper 3. Length 4. Roundness 5. Straightness of taper 6. Datum step (where applicable) 1. Straightness of cylinder sides 2. Flatness of end faces 3. Squareness of cylindrical surface to end faces 1. Flatness 2. Parallelism and squareness of working surfaces 3. Flatness and squareness of front and back surfaces 1. Flatness and squareness of working faces 2. Parallelism of longitudinal and opposite end faces 3. Squareness of working faces to end faces 1. Deviation from nominal length 2. Deviation from nominal at suitable intervals 3. Squareness of ends (steel rules) SANAS Page 6 of 15

7 TAPES AND WIRES SCREW RING TAPER (ANTP AND BSPT) SCREW PLUG TAPER (ANTP AND BSPT) GAP GAUGES ENGINEERING PARALLELS VEE BLOCKS STRAIGHT EDGES ROUNDNESS STANDARDS TRIPOINT INTERNAL MICROMETERS STICK MICROMETERS EXTERNAL MICROMETERS DEPTH MICROMETER VERNIER CALLIPERS 1. Deviation from nominal at suitable intervals 2. Chord length with catenary correction 3. Mass per unit length 4. Tension 1. Simple eflective diameter at specified points 2. Angle of taper 3. Tolerance step 1. Simple eflective diameter at specified points 2. Angle of taper 3. Tolerance step 1. Dimensions across faces 2. Parallelism where applicable 1. Squareness 2. Straightness 3. Parallelism 4. Thickness and width 5. Equality of pairs 1. Flatness of faces 2. Parallelism of opposite faces 3. Squareness of adjacent exterior faces 4. Parallelism of Vee axis to side faces 5. Centrality of Vee 6. Equality of matched pairs 7. Equality of semi-angle of Vee 1. Straightness of working faces 1. Radial error. (Spherical) 2. Radial error and squareness to base (Cylindrical) 1. Micrometer screw error 2. Set to zero 1. Error in length of each extension rod when thimble reads zero 2. Micrometer screw error 1. Flatness of measuring faces 2. Parallelism of measuring faces 3. Zero reading 4. Micrometer screw error 1. Micrometer screw error 2. Flatness of base 3. Error in length of each extension rod when thimble reads zero 1. Parallelism of outside jaws 2. Straightness and parallelism of inside jaw or knifeedges 3. Accuracy of sliding scale in 5 to 8 positions 4. Repeatability of dial if present 5. Zero setting of depth rod SANAS Page 7 of 15

8 VERNIER HEIGHT GAUGES VERNIER DEPTH BEVEL PROTRACTORS MECHANICAL OR OPTICAL ROUNDNESS MEASURING INSTRUMENT SURFACE TEXTURE BORE COMPARATOR 1. Flatness and parallelism of working faces of measuring jaw (when applicable) 2. Parallelism of fneasuring jaw and scriber to base 3. Flatness of base 4. Accuracy of reading of beam and vernier scale at 5 to 8 places along working length 1. Flatness of stock face 2. Readings at a minimum of 3 equidistant positions throughout range 1. Straightness of working edge of stock 2. Straightness of working edge of blade 3. Parallelism of working edge of blade 4. Error of indication in blade positions at specified intervals 1. Radial error 2. Magnification 3. Axial error of instrument 4. Straightness of column if applicable 5. Squareness 1. Parameters and magnification according to standard available 1. Repeatability of measurement 2. Accuracy of setting masters 3. Accuracy of Dial / Analogue / Digital read-out if present SANAS Page 8 of 15

9 6. Guidelines on Determining the Suitability for Calibration of Instruments or Gauges with Particular Reference to the Issuing of SANAS Certificates 6.1 It is most important that the status and credibility of SANAS calibration certificates be upheld. 6.2 SANAS Criteria for the approval of laboratories are designed to ensure that Accredited Laboratories can guarantee traceability at a suitable, known level of accuracy. 6.3 Individual gauges which form part of a set, are required to be identified individually so that the user has traceability to each individual gauge. Where gauges are individually marked, the serial numbers shall be recorded on the calibration certificate. Where gauges are not individually marked, the serial number of the set shall be used. 6.4 Although accuracy of calibration of an instrument can be defined only at the time of the actual performance of that calibration, the subsequent stability of the instrument can have a decided influence on the apparent value or credibility of the calibration certificate, it is therefore most undesirable for SANAS Accredited Laboratories to issue certificates of calibration for obviously unstable devices. 6.5 The status of a SANAS certificate can also be affected by the appearance of the gauge or instrument for which it is issued. 6.6 On the other hand: i) Instruments must be calibrated to ensure accuracy at whatever level they are used. An inaccurate tape measure may have an even more dangerous influence than an inaccurate gauge block. ii) iii) For the purchaser of calibration services the guarantee of traceability is extremely important. Heads of SANAS Accredited Laboratories must do all in their power to satisfy the demand for calibrations whose traceability is guaranteed by SANAS certificates. SANAS Page 9 of 15

10 APPENDIX 1: Schedule of Accreditation SCHEDULE OF ACCREDITATION DIMENSIONAL METROLOGY Laboratory Accrediattion Number: 1234 ITEM Measured Quantity or type of gauge or Instrument Range of Measured Quantity Frequency, Standard, etc Calibration and Measurement Capability (CMC) Expressed as an uncertainty (±) 2.3. Line Standards Precision line scale Stage micrometer Grid plate One dimension grating Two dimension grating Linewidth standard Surveyor / Engineer measuring tape ( Pi) 0 mm to 100 m (0,4 + l x 10-4 ) l in mm Surveyor levelling rod Engineers or machinest scale (Fish length board) 2.4 Diameter Standards 0 mm to mm 25 µm External cylinder(plug, piston, pin, wire) 1 mm to 50 mm 0,5 µm Internal cylinder (ring) 3 mm to 6 mm 0,5 µm Sphere (ball) 3 ANGLE 3.1 Angle by circle dividers Polygon Index table Rotary table 3.2 Small angle generators Sign bar or table 3.3. Angle Instruments Autocollimator Electronic Level 2 µm/m Clinometer Up to SANAS Page 10 of 15

11 3.3.4 Spirit Bubble Level 2 µm/m Theodolite (Bevel) protractor Squareness tester 3.4 Angle artefacts Angle block Steel, granite square Up to 600 mm 5,0 µm Cylinder square Up to 600 mm 5,0 µm Cone (taper) gauge (External/Internal) 3.5 Angle prisms Optical square Retroreflection (cube-corner, cat eye)prism 4 FORM 4.1 Flatness standards Optical flat Optical parallel Up to 600 mm 5,0 µm Surface Plate/Table Up to 3000 mm 4 µm/m 4.2 Roundness standards External Cylinder 1 mm to 50 mm 0,5 µm Internal Cylinder 3 mm to 6 mm 0,5 µm Sphere or hemisphere Magnification standard (Flick) 4.3 Straightness standards Straight edge Up to 3000 mm Cylindrical straightness standard Straightness of guideway 4.4 Cylindricity standards External cylinder Dependant on overall performance Internal cylinder 4.5 Optical standards Lens, radius standards 5 COMPLEX GEOMETRY 5.1 Surface texture standards Groove (depth) or step height standard Tip-condition standard SANAS Page 11 of 15

12 5.1.3 Spacing standard Roughness standard (Ra, Rt,Rz) Profile coordinate standard 0,8 µm 0,2 µm Soft gauge standard 2.3 Line Standards Precision line scale Stage micrometer Grid plate One dimension grating Two dimension grating Linewidth standard Surveyor / Engineer measuring tape ( Pi) Surveyor levelling rod 0 mm to 100 m (0,4 + l x 10-4 ) l in mm Engineers or machinest scale (Fish length board) 2.4 Diameter Standards External cylinder(plug, piston, pin, wire) 0 mm to mm 1 mm to 50 mm 25 µm 0,5 µm Internal cylinder (ring) 3 mm to 6 mm 0,5 µm Sphere (ball) 3 ANGLE 3.1 Angle by circle dividers Polygon Index table Rotary table 3.2 Small angle generators Sign bar or table 3.3 Angle Instruments Autocollimator Electronic Level 2 µm/m Clinometer Up to Spirit Bubble Level 2 µm/m Theodolite (Bevel) protractor SANAS Page 12 of 15

13 3.3.7 Squareness tester 3.4 Angle artefacts Angle block Steel, granite square Cylinder square Cone (taper) gauge (External/Internal) 3.5 Angle prisms Optical square Retroreflection (cube-corner, cat eye)prism 4 FORM 4.1 Flatness standards Optical flat Optical parallel Up to 600 mm Up to 600 mm Up to 600 mm 5,0 µm 5,0 µm 5,0 µm Surface Plate/Table Up to 3000 mm 4 µm/m 4.2 Roundness standards External Cylinder 1 mm to 50 mm 0,5 µm Internal Cylinder 3 mm to 6 mm 0,5 µm Sphere or hemisphere Magnification standard (Flick) 4.3 Straightness standards Straight edge Cylindrical straightness standard Straightness of guideway 4.4 Cylindricity standards External cylinder Internal cylinder 4.5 Optical standards Lens, radius standards 5 COMPLEX GEOMETRY 5.1 Surface texture standards Groove (depth) or step height standard Tip-condition standard Spacing standard Roughness standard (Ra, Rt,Rz) Profile coordinate standard Up to 3000 mm 0,8 µm Dependant on overall performance 0,2 µm SANAS Page 13 of 15

14 5.1.6 Soft gauge standard Original date of accreditation: 1980 The CMC, expressed as an expanded uncertainty of measurement, is stated as the standard uncertainty of measurement multiplied by a coverage factor k = 2, corresponding to a confidence level of approximately 95% SANAS Page 14 of 15

15 ADDENDUM 1. AMENDMENT RECORD Proposed By: Section Change STC 1 Added last sentence STC 2 Added reference to the Accreditation Act STC 3.2 Test measurements changed to Calibration measurements STC 3.3 NMISA replaced NML STC Appendix 1 Appendix 1 introduced SANAS Page 15 of 15