EN 4861-2020 pdf download.Aerospace series – Metrological assessment procedure for kinematic fields measured by digital image correlation.
The calibration apparatus should be calibrated and should meet the performance requirements given in
Table B.1.
6.2 Traceability of metrological performance assessment
The calibration apparatus and the supporting equipment (such as micrometres, callipers, and optical projection microscopes) shall be calibrated using standards that are traceable to the International System of Units (SI).
The uncertainty associated with any measurement made by the supporting equipment shall not exceed one third of the allowable error of the extensometer system being calibrated, see Table 2. The temperature measurement instrument shall have a resolution of 0,1 °C.
7 Pre-assessment inspection
7.1 Aim
Prior to the assessment, the extensometer system shall be inspected. The quality of mechanical, optical, electronic components and devices have been validated in terms of equipment such as the free motion of tables, lenses, wiring and connections, hard drive space.
The extensometer system shall be assessed In the as-found condition if at all possible. The results shall be analyzed and, if necessary, the system shall be adjusted and re-assessed. In this case, both data sets shall be reported.
7.2 Records of the inspection
Records of the pre-assessment inspection shall be kept, identifying the ‘as-found” condition of the extensometer system, when the inspection was performed and who performed it. These pre-assessment inspection records can take the form of either a written report or a completed pro-forma” checklist.
7.3 Identification of extensometer system elements
The extensometer system shall be uniquely identified. Parts that may be changed by the user during normal use of the extensometer system that affects the metrological assessment of the extensometer system shall also be uniquely identified whenever possible (e.g. camera, lens, lighting). These unique identifiers are part of the records for the extensometer system. It will enable each component of the system and the adjustment parameters to be referenced (e.g. lens settings, calculation parameters of digital image correlation).
The measurement of the physical size of the pixel is performed according to the measuring system manufacturer specifications.
8.2 Case od monovision measurements – manual procedure
The measurement of the physical size of the pixel is performed according to the internal procedure of the user. The procedure and the result of this measurement shall be documented.
8.3 Case of monovision measurements – identification during the performance assessment procedure
An alternative is to consider an identification procedure proposed in Annex E. This procedure requires the user to be able to export the displacement field measurements in pixels with the extensometer system and metric measurements for the evaluation of the metrological performance.
8.4 Case of stereovision measurements
This measurement is not applicable because it is treated during the calibration step of stereocorrelation
codes.
9 Metrological assessment process
9.1 Environmental considerations
9.1.1 General
The ambient temperature during the metrological performance assessment of the extensometer system shall be recorded.
In general, the calibration of the extensometer system should be carried out at a temperature stable to within ± 2 °C, the target temperature being within the range of 18 °C to 28 °C. Temperature changes during the metrological performance assessment process may add to the uncertainty of the calibration and in some cases may affect the ability to properly assess the metrological performance of the extensometer system.
For extensometer systems used at temperatures outside the recommended range of 10 °C to 35 °C, the metrological assessment should be carried out at or near the test temperature. If facilities exist.
The extensometer system shall be placed near the system for the assessment of the metrological performance, or be mounted on it, for a sufficient duration prior to its assessment so that the parts of the extensometer system and of the system for the assessment of the metrological performance that are in contact stabilize at the metrological assessment temperature.EN 4861-2020 pdf download.