The XL Achieves
Precision and Bias
A Report of Round Robins and Workshops Conducted with the XL Slipmeter
Last update by William English July 26, 2003
There was also a limited workshop for interested XL slipmeter
users at the January 1998 F13 meeting in San Diego where they got together
informally on Sunday evening to test the same surfaces with every participant
observing and critiquing everybody else’s operating technique. I was not
able to attend that meeting, but reportedly progress was made and the outliers
were brought into the fold as far as test results are concerned. Jim
Flynn of J2 Engineering in Fresno, CA was the denmother of all
of these experiments.
Following that first workshop, a couple of "mail-order" round robins were conducted in which the same three test surfaces were circulated to seven different labs and everybody used the same test foot. The purpose was to establish that the meters produced repeatable results in different labs.
In the third "mail-order" round satisfactory precision and bias were achieved, and David Underwood, PhD, produced a statistical evaluation using ASTM E691 software, including the following summary, which compares the XL’s performance with the other slipmeters for which precision and bias figures are published in their respective ASTM standards.
For the VIT
Dry reproducibility: std. deviation 0.02, wet reproducibility: std. deviation 0.03 (testing performed on 3 surfaces using 6 testers) This fine precision compares favorably with traditional slipmeters:
C1028 Horizontal Pull Dynamometer
Dry reproducibility: std. deviation 0.07, wet reproducibility: std. deviation 0.05 (testing performed on 1 surface using 6 testers)
D2047 James Machine
Dry reproducibility: std. deviation 0.03?*, not used fore wet testing. (testing performed with a leather foot using 3 testers)
F609 Horizontal Pull Slipmeter
Dry reproducibility: std. deviation 0.07,* not used for wet testing, (testing performed on 2 surfaces, 17 kinds of feet, using 4 testers)
*Procedure for establishing this figure is not clear—consult original ASTM research report for more detail
Just to put the icing on the cake, on the evening of June 8, 1998 ( in conjunction with the F13 meeting) another VIT workshop was conducted concerning the repeatability of Neolite® as a friction pad material. Results of this study were published at the January F13 meeting in Memphis. They were very good. Using ten different test feet of different ages and from different production batches, Jim Flynn obtained repeatability virtually as good as was obtained in the round robins where the same test foot was used on all machines. So Neolite® is the hands-down winner of the consistency derby for test foot friction pad material! Another Neolite® workshop was conducted in connection with the June 1999 F13 meeting. Preliminarily these results also appear promising, but complete analysis is still in process.
A more recent precision study was conducted in conjunction with the January 2000 F13 meeting in New Orleans, and eleven operators using eleven VITs, each with his own testfoot, produced approximately the same precision as the single foot on six machines. These tests show that Neolite® variability does not have a major effect on the XL output, even with the larger number of participants.
In additional to the slipmeter output numbers,
Shore A and Shore D hardness of the testfeet was measured, and no
clear link between Neolite® hardness
and slipmeter output was observed, and the repeatability was as good as
in the prior studies.
See statistical analyses of the January 2000 New Orleans P&B workshop in the Second Edition of Pedestrian Slip Resistance.
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