As the largest source of dimensional measurement uncertainty, addressing the challenges of thermal variation is vital to ensure product and equipment integrity in the factories of the future. Whilst it is possible to closely control room temperature, this is often not practical or economical to realise in all cases where inspection is required. This paper reviews recent progress and trends in seven key commercially available industrial temperature measurement sensor technologies primarily in the range 0-50˚C for invasive, semi-invasive and non-invasive measurement. These sensors will ultimately be used to measure and model thermal variation in the assembly, test and integration (AIT) environment. The intended applications for these technologies are presented alongside some consideration of measurement uncertainty requirements with regard to the thermal expansion of common materials. Research priorities are identified and discussed for each of the technologies as well as temperature measurement at large. Future developments are briefly discussed to provide some insight into which direction the development and application of temperature measurement technologies are likely to head.

Thermal effects in uncontrolled factory environments are often the largest source of uncertainty in large volume dimensional metrology. As the standard temperature for metrology of 20˚C cannot be achieved practically or economically in many manufacturing facilities, the characterisation and modelling of temperature offers a solution for improving the uncertainty of dimensional measurement and quantifying thermal variability in large assemblies.Technologies that currently exist for temperature measurement in the range of 0-50˚C have been presented alongside discussion of these temperature measurement technologies' usefulness for monitoring temperatures in a manufacturing context. Particular aspects of production where the technology could play a role are highlighted as well as practical considerations for deployment.Contact sensors such as platinum resistance thermometers can produce accuracy closest to the desired accuracy given the most challenging measurement conditions calculated to be ~0.02˚C. Non-contact solutions would be most practical in the light controlled factory (LCF) and semi-invasive appear least useful but all technologies can play some role during the initial development of thermal variability models. Main textIn large volume metrology, thermal effects make a significant contribution to the uncertainty of measurements. Large structures that are often 20 m in length or greater are currently being assembled in factory environments where there can be thermal gradients of around 3-5˚C from floor to ceiling at any given time. Over a 24 hour cycle, the variation in ambient temperature can be as much as 15˚C.Whilst dimensional measurements in industry are sometimes taken alongside ambient temperature measurements which are used for linear scaling within the metrology software, this is often a sole measurement at one point in space, at one instance.One potential solution to the problem of thermally induced uncertainty is to model the thermal characteristics of the measurand. This can be achieved by monitoring the temperature and using this data to update a computational model that can more accurately predict the thermal and gravitational effects of the environment. The computational model makes use of the nominal CAD geometry of the measurand, alongside finite element analysis and tolerancing software.

Abstract. Ideally metrology is undertaken in well-defined ambient conditions. However, in the case of the assembly of large aerospace structures, for example, measurement often takes place in large uncontrolled production environments, and this leads to thermal distortion of the measurand. As a result, forms of thermal (and other) compensation are applied to try to produce what the results would have been under ideal conditions. The accuracy obtained from current metrology now means that traditional compensation schemes are no longer useful. The use of finite element analysis is proposed as an improved means for undertaking thermal compensation. This leads to a "hybrid approach" in which the nominal and measured geometry are handled together. The approach is illustrated with a case study example.

Control of temperature in large-scale manufacturing environments is not always practical or economical, introducing thermal effects including variation in ambient refractive index and thermal expansion. Thermal expansion is one of the largest contributors to measurement uncertainty; however, temperature distributions are not widely measured. Uncertainties can also be introduced in scaling to standard temperature. For more complex temperature distributions with non-linear temperature gradients, uniform scaling is unrealistic. Deformations have been measured photogrammetrically in two thermally challenging scenarios with localised heating. Extended temperature measurement has been tested with finite element analysis to assess a compensation methodology for coordinate measurement. This has been compared to commonly used uniform scaling and has outperformed this with a highly simplified finite element analysis simulation in scaling a number of coordinates at once. This work highlighted the need for focus on reproducible temperature measurement for dimensional measurement in non-standard environments.

No abstract