How Important is Temperature Scale, and What Methods of Scaling are Best for Portable Metrology?by Richard Nelson on August 3, 2017 From Ask The Experts
Although we now have portable and stationary measuring systems which are far more robust having been designed to withstand many environmental changes, for example on the shop floor, the objects being measured are not. Technicians still need to account for changes in the size of parts being measured as temperature shifts can have a huge impact on critical metrology test results.
For example, a two-metre aluminium bar will grow 0.47 mm (0.019 in) as the temperature increases by 10°C (18°F). It might not sound like a huge proportion of the bar, but it is a significant shift to a metrologist and these shifts must be taken into account in order to make accurate comparisons to a design part.
Scale in SpatialAnalyzer® is applied as a property of a measurement station. As temperature changes during measurement, new stations can be added. By scaling the measurements to a consistent reference temperature, all the stations can easily be networked together for an accurate comparison to a design part.
As for what methods of inspection are best, it really depends on the situation. If an accurate delta temperature can be obtained, scaling based on Coefficient of Thermal Expansion (CTE) is ideal. The core temperature of the object must be accurately measured to ensure sound results.
Alternatively, you can use the measurements themselves to establish scale, which is known as Best-Fit Scaling (7DoF fits). Allowing scale to float during a best-fit works well with a set of reference points integrated into the part; however, establishing the network at a known temperature is required.
Richard Nelson is a Senior Applications Engineer at New River Kinematics (NRK) and member of the American Society for Quality. Prior to joining NRK, Richard worked in design and quality engineering within the transport and aerospace industries. He is now using his extensive experience to provide innovative solutions in portable metrology with SpatialAnalyzer® software.