Accuracy, precision, stability and traceability
When using 3D scanning as a measurement system, it is important to understand aspects which contribute to a high level of confidence in the delivered results. Physical Digital undertakes project specific and long-term monitoring of these key performance indicators to ensure high measurement stability and provide unrivalled confidence in the results it delivers. These aspects differentiate Physical Digital from all other providers of 3D scanning in the aerospace industry and provide an industrial measurement solution in-line with traditional CMM measurements, with the advantage of full-surface data capture. Precision Precision can be shown in many forms, however the simplest way to understand this is by looking at the spread of results produced when taking the same measurement. Range is the basic form of this and shows the variation across the measured sample. It is also common to use statistics to extrapolate the range given any sample size. Precision should be the starting point of any measurement understanding, without a precise measurement system it is difficult to have confidence in the results produced and the measurement process is technically out of control. Physical Digital can provide supporting studies to any customer specification and typically use AS13003 as a standard when performing these for our aerospace customers. Accuracy Accuracy is the error between the measurement result and a known value, this is the bias of the systems and, providing the measurement is precise, can be easily compensated back to a nominal result if required. Accuracy can be calculated back to a golden part or calibrated artefact and provides a method of validating results against a known reference standard. Physical Digital continuously evaluates accuracy via the VDI/VDE 2634 Standard with artefacts of <1µm uncertainty. Stability The ability to produce the same measurement over any extended period is an important factor when undertaking long-term projects. Physical Digital operates Statistical Process Control (SPC) to monitor and maintain our systems over time and provide confidence to customers that results are stable over our long-term support contracts. Traceability Traceability is the ability to provide an unbroken chain of comparisons from a known standard to the delivered results. 3D scanning systems have historically lacked this; however Physical Digital maintain the highest level of industry calibration and traceability and utilise the GOM photogrammetry systems with traceable artefacts of less than <1µm uncertainty.