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There are special considerations concerning R0, or Bird Bath Error. Trackers which are equipped with both ADM and
IFM may have an R0 coefficient for each measurement mode. Care must be taken to test each mode for this error.
KinAiry software will prompt an additional measurement step if a laser tracker is selected which operates in ADM and
IFM mode. Further detail is available in the documentation for the NIST Interim Field Test
[5]
.
Results
Traceability
Once all measurement points are complete and recorded, measurement errors can be calculated. For two-face errors,
the error is taken as the distance between the front and back-face measurement points for each target and test
position. For length measurements, the error is taken as the difference between the measured lengths in front face
only and the calibrated lengths.
The error values summarize the volumetric measurement performance of the laser tracker. They describe the
measurement error of the tracker in the conditions which it’s operating, and can be compared against other results
taken over time, results taken at the time the tracker is factory calibrated, error limits for an internal quality system, or
published MPEs.
The NIST Interim Field Test relies upon measurements of points and calculated distances between points. Traceability
of those measurements can be maintained following guidance from standards like: ASME B89.7.5, JCGM 200:2012, or
ILAC P10:01/2013. It is important to note that the documentation of traceability to a metrological terminus is intended
to come from the calibration of the laser tracker range system used to establish the reference length.
