InteraqCT Comparison on Assemblies - Final Report

Alessandro Stolfi, Leonardo De Chiffre

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    An interlaboratory comparison on industrial X-ray Computed Tomography (CT) was organized by the Centre for Geometrical Metrology (CGM), Department of Mechanical Engineering, Technical University of Denmark (DTU) and carried as part of the Marie Curie ESR Project INTERAQCT. In the comparison, 22 laboratories from 7 countries were involved, and two assemblies, Assembly 1and Assembly 2, having different materials and sizes were circulated. Assembly 1 is a physical item while Assembly 2 is a CT scan of industrial assembly. Various measurands are considered, encompassing lengths, diameters, roundness and concentricity. A multi-material length is also included in the comparison. Two different scanning approaches were considered within the comparison exercise for Assembly 1. The first approach, coded as “Own Choice”, does not apply any scanning restrictions on any of the scanning parameters. The second one, coded as “FastScan”, introduced a series of limitations, including the scanning time and the number of images perprojection. 22 samples of Assembly 1 were circulated in parallel to the participants. A single sample of Assembly 2 was electronically circulated to the participants. The results of each participant are kept confidential. Participants can identify their individual results using an anonymous identification number provided by the coordinator at the beginning of the circulation. All samples were measuredby the coordinator using a coordinate measuring machine before and after circulation. The samples of Assembly 1 have shown a good stability over the total comparison time of 8 months. No stability investigation was conducted on Assembly 2 due to the absence of circulation. Depending on the item and measurand, the reference expanded uncertainties (k=2) ranged from 1.1 μm to 2.6 μm. Participants stated measurement uncertainties in the range between 2 μm and 100 μm for all measurands of Assembly 1. The majority of participants stated measurement uncertainties based on MPE, whereas just a few participants used more complex uncertainty models. The metrological consistency of participants´ results was investigated using the En value, where |En| < 1 indicates agreement between measurement results while |En| ≥ 1 shows disagreement. 71% of the measurements conducted using the Own Choice approach are in agreement with the reference values. 59% of the measurements carried out using the Fast Scan approach are in accordance with the reference values. L2, L3, and T, which are bidirectional measurands, show lower agreement than L1 and L4, which are unidirectional lengths. The majority of participants obtained similar results in both scanning approaches. A few participants achieved significantly different measurement results, most probably due to the impossibility of selecting suitable scanning parameters. Systematic errors were detected for some participants, especially in CT systems not built for metrology. Results for Assembly 2 showed that increasing the complexity of the measurand increases the range of variation among participants. A good agreement was obtained among InteraqCT_FinalReport Page 4 of 74 participants for diameters, whereas a worse agreement was registered for roundness and concentricity. It was also observed that participants obtained different results although they used similar inspection software and measuring strategies. Measuring procedures provided by the coordinator for both assemblies were followed by participants without problems. Most participants carried out measurements and sent their results to the coordinator according to the schedule.
    Original languageEnglish
    Number of pages74
    Publication statusPublished - 2016

    Bibliographical note

    The InteraqCT comparison on assemblies is as an activity within the Marie Curie ESR Project INTERAQCT - International Network for the Training of Early stage Researchers on Advanced Quality Control by Computed Tomography funded by the European Commission's 7th Framework Programme FP7-PEOPLE - Under grant agreement No 607817. Detailed information is available at


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