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B
Additional Methodology
B.1.
B.1.1.
Gage Linearity and Bias Study for Force Measurements
Background
A Gage Linearity and Bias procedure was used to estimate the accuracy of the force measurement
system. The force measurement system is accurate if the bias is small. Bias indicates how close
the measurements are to the reference values. Linearity refers to the how much the bias changes
throughout the normal operating range of the measurement system. If the bias is consistent, then
the linearity is small. The objective of this study was to compute the linearity and bias values of
the force measurement system for the uncertainty analysis.
B.1.2.
Procedure
Four reference loads (M1 = 98 N, M2 = 196 N, M3 = 294 N, and M4 = 392 N) were placed on the
geometrical center of the top plate of the two force platforms and 50 repeated measurements were
recorded for 5 sec each at sampling rate of 30 Hz. The mean value (and standard deviation) was
computed for each sample. The study performed by one operator.
B.1.3.
Statistical Analysis
The Grubbs’ test was used to check for outliers. A regression line was fitted on the bias against the
reference values and statistics for the linearity and accuracy of the measurement system computed.
It is assumed that biases are corrected by the manufacture’s calibration procedure, therefore, only
the uncertainties of the correction are presented. The range over which the measurements varies
due to normal variation computed by the R&R study (Table B.2).
B.1.4.
Results Report
Table B.1 shows the results of the analysis. The maximum absolute value of the bias per part
(load) and the linearity values were added to the uncertainty budget for calculating the expanded
uncertainty of the measurement system (Table 3.3). Based upon a total of 200 measurements
(mean values) on 4 parts (M1→4 ), the estimated mean bias of the force platform 1 was −2.92 N
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