Calculating Measurement Uncertainty for Durometers

[Joe Ruland]

I am confusing myself trying to figure the uncertainty for Durometers. I have computed by repeatability in Dura. I have taken the half interval of the resolution & divided by the square root of 3.

The pooled uncertainty of my weights used as a standard is .0612 gram.
I believe that all uncertainties must be in the same units so how can I convert grams to Dura? Is there a uncertainty example out there for durometers?

[Charles Wathen]

I was curious to this as well, and I emailed the people at Shore. I got this response from Mike:
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Refer to ASTM D2240-03, Table 1 is the chart for spring force calibration for all durometer types. The values are given in N for durometer values 0-100 in increments of 10. The "N per durometer unit" is also given. Simply convert N to gf and use these values for your purpose.

The method is available from ASTM at:
http://www.astm.org/cgi-bin/SoftCart.exe/STORE/filtrexx40.cgi?U+mystore+kfcm7012+-L+D2240NOTSTATUS:<NEAR/1>:REPLACED)+/usr6/htdocs/astm.org/DATABASE.CART/REDLINE_PAGES/D2240.htm

If you should have further questions, please do not hesitate to contact me directly. It should give you some comfort to know that I am the Chairman of ASTM D11.10.02 (the Task Group on Durometer Hardness) and the author of the test method.

Highest Regards,
Michael Kent Warner

OREC™ Ozone Research Equipment
A Wholly Owned Subsidiary of CCSi, Inc.
Florida Office
1219 SW 1st Place
Cape Coral, Florida 33991-2806
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Looking at the table that Mike refered to, type A, B, E, and O would be .075 N/durometer unit or 7.6478716 grams.
C, D, DO: 0.4445 N/durometer unit
M: 0.0044 N/durometer unit
O, OOO: 0.00908 N/durometer unit
OOO-S: 0.01765 N/durometer unit