CP-003 Calibration of Vernier Caliper [PDF]

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CP-003 CALIBRATION OF VERNIER CALIPER. REFERENCES: IS: 3651(PART 1)-1982 (REAFFIRMED 2005) IS: 3651(PART 2)-1985 (REAFFIRMED 2005) ASME B89.1.14-2018 Nomenclature of digital and analogue Vernier calipers: ISO1.017025



2.0 Scope: 2.1 Covers the methods of testing the accuracy of Digital, Dial and Analogue Vernier Caliper. 3.0 Cleaning: 3.1 Prior to use and again after use and prior to storage, measuring instruments should be cleaned to remove contaminants. 3.2 Clean the measuring faces by inserting lint free paper between them, lightly close, and pull the paper through. 3.3 Callipers can be cleaned by using a soft brush or clean cloth and solvent. 3.4 Care should be taken to prevent trapping of solvent in holes or crevices. 3.5Avoid spraying solvent directly on the dial or electronic digital display. 4.0 Equipment Required (Standards): 4.1 Measuring Ceramic Gage blocks 4.2 Calliper checker (Mitutoyo) 4.3 Calibrated Ring gauge 4.4 Calibrated Surface plate. 5.0 Visual Inspection: 5.1 The measuring faces should be inspected for any damage or excessive wear and thoroughly cleaned. Verify smooth movement of the slide along the bar. The zero reading of the measuring faces should be checked. 6.0Frequency of calibration: 6.1 The frequency of calibration for digital, dial and Analogue Vernier Callipers is 6 months if calibrated in house ** 7.0Traceability: 7.1 All standards, used in determining the conformance of a Digital, Dial and Analogue Vernier Calliper to specifications, must have traceability to National or International standards e.g. (NABL, NIST) 8.0 Soak time: 8.1 Measuring instruments should be stored in a constant temperature room before they are calibrated to ensure they are nearby the same temperature as the measurement laboratory. Gages must soak in the calibration lab for 15 minutes per inch of gage length prior to calibration



9.0 Accuracy Specifications: 9.1 Two accuracy specifications cover the most important metrological



characteristics of callipers. In accordance to the ASME Standard, as well the international standard ISO 13385-1, these two characteristics are called the partial surface contact error, E and the scale shift error, S. 9.2 The partial surface contact error applies to any measurement made using the outside measuring faces. 9.3 The scale shift error applies to measurements using any other measuring faces available on the calliper such as inside, step and depth measurement. 9.4 The key difference is that all specifications apply when the zero is set using the outside measuring faces and therefore there is a possibility of large errors when using the other measuring faces. 9.5 The table below lists the default specification values that are in the ASME B89.1.14 standard. These specifications are stated as Maximum Permissible Errors, or MPE values, for the E and S errors. TABLE 1



10.0 Procedure: 10.1 The most important aspect of the calibration of a calliper is to verify conformance with stated accuracy specifications. In accordance with ASME B89.1.14 standard, the conformance verification test for EMPE and SMPE are described below.



10.2 Using the outside measuring faces, conformance to EMPE is verified by measuring gage blocks, a calliper checker or other reference standards across the measuring range of the calliper. A minimum of three to five test points is required depending on the measuring range of the calliper. Measuring Range M mm 0 ≤ M ≤ 150 150 < M < 300 300 < M ≤ 1000



in 0≤M≤6 6 < M ≤ 12 12 < M ≤ 40



Minimum Number of Test Points 3 4 5



10.3 At least 90% of the measuring range shall be covered. 10.4 In addition, the reference standards shall be located at various positions on the measuring faces, from close to beam to near the tip of the jaws.



10.5 Prior to testing for line contact error, assessment of the possibility of wear or parallelism issues by bringing the outside measuring faces together and observing any light gap between the two measuring faces is recommended. If wear or parallelism is not suspected, then additional testing of the line contact error with the cylindrical measurement standard may not be necessary. 10.6 The line contact error L, is the error of indication when measuring a small



cylindrical measurement standard e.g. a pin gage, at any position across the outside measuring faces. This error is calculated as the maximum difference (range) between the line contact error observed at any position on the outside measuring faces and at the same nominal position in the measuring range of the calliper 10.7 The line contact error detects the effects of the parallelism of the outside measuring faces as well as any flatness error or localized wear. When testing for conformance to specification, the line contact error shall be tested at one position in the measuring range of the calliper. This is done by placing a small cylindrical measurement standard between the jaws as near as possible to the calliper’s beam, and then slowly moving the measurement standard towards the opposite end of the jaws while carefully observing the callipers readings. The range of readings is the line contact error. 10.8 Conformance to SMPE must be verified for all the other modes of operation that are possible with the calliper with at least a single test point. 10.9 The reference standard for testing the inside measurement is typically a Calliper checker, a Ring gauge or gage blocks and accessories. The default size for testing is between 0.75 in (20 mm) and 2 in (50 mm). 10.10 For depth and step measurements, the reference standard is typically a Gage block on a surface plate. A square gage block provides a useful hole to insert the depth bar. By default, the size for testing should be less than 2 inches (50 mm).



10.11 The internal measuring faces on many styles of callipers use crossed knife-edges. Due to the thickness of the faces and clearances between them, additional errors can occur when measuring small internal diameters. 10.12 For callipers that utilize cross knife-edge measuring faces, ASME B89.1.14 requires an additional test using a 0.2 in (5 mm) diameter Ring gage for all callipers with measuring ranges up to 12 in (300 mm) 11.0 Tolerance:



11.1 The Tolerance is as per Table No 1. 12.0 Documentation: 12.1 Proceed to measure the specified points listed in the Gage management Software. Record the results in the Gage Management Software. 12.2 A register of the monitoring and measuring equipment shall be maintained. The register shall include the equipment type, unique identification, location, and the calibration method, frequency and acceptance criteria. 12.3 Old calibration stickers shall be removed and new calibration stickers filled out and properly affixed. 13.0 Packing and Preservation: 13.1 For storage, shipment between facilities or shipment from a facility to a Calibration laboratory, measuring instruments should be coated with a corrosion preventative as soon as possible after cleaning operations. 13.2 The corrosion preventative to be used will depend on the type of measuring instrument being stored or shipped. 13.3 An approved rust-preventative (light, medium or heavy) should be used. 13.4 Close-tolerance gauging surfaces should be coated with an approved light preservative. 13.5 Store the calliper with a gap between the outside measuring faces. ** Customer requirements supersede the requirements of this procedure.