rement areas.
Results of Temperature CorrectionIf temperature compensation is necessary, one cannot assume there will be no more temperature influences. Despite the correction for thermal influences, there is a remaining measurement uncertainty that is lower when the expansion coefficient of the workpiece is known and the temperature is measured more precisely. (See Table 2.)
Limit deviation is defined as the maximum possible (estimated) deviation from the true value. It is assumed to be distributed rectangularly.
According to international standards, the expanded measurement uncertainty is the standard deviation multiplied by the expansion factor k=2. Therefore, it applies to a confidence interval of 95%.
For the selected measurement example, it is assumed that the temperature can be measured at a limit deviation of 0.5 K. The expansion coefficient of the workpiece is known with a maximum deviation of 5%. A measurement uncertainty of 16 microns thus remains. Here, that is only 7.7% of the original error of 207.8 microns without correction.
Tips for Practical ApplicationTemperature correction is more reliable and effective if the following actions are taken:
- Allow as little temperature change as possible.
- Avoid air drafts.
- Enclose the devices if rapid changes in temperature
- Keep heat sources in constant operation.
- Install devices at least 1 meter from the walls.
- Thermally insulate the floor.
- Do not allow direct sunlight.
- The measured object should be at the ambient
- Avoid touching parts with hands, or wear gloves.
- Ensure constant temperature during a measurement
- Carry out a drift check by reviewing the reference coordinate system, for long measurement cycles.
must sometimes measure at temperatures that deviate greatly from calibration
- For measuring small lengths, a simple linear correction in each
measurement axis can be implemented at a
- Lengthwise expansions of the scale and workpiece can compensate for
one another if the scale and workpiece are made of the same
- New modular CMMs measure temperatures with sensors and use scales to calculate thermal expansion automatically.