In Reply to Parent Post by jfgunn
Couple of thoughts:
1.) You use the acuracy of gage blocks in your calculation. This is correct. You should also have a factor equal to the calibration of the gage blocks. When you had your blocks calibrated, you were given an uncertainty at k=2. Take this number and use a divisor of 2.
2.) It would appear that the bench micromter you are to test has a resolution of 20 millionths. I would use 1/2 this value for the contributing factor, therefore 10 millionths.
3.) I would reccomend calculating the uncertinaty at 1, 5, and 10 inches. you could then have a statement of the uncertainty that has the form something like "(16 + 3L)uin where L is the length in inches".
4.) Is your bench micrometer the only one you will be testing? If so, you temperature stability numbers look OK. If not, you should allow for a larger swing of temperature for on-site work where the lab is not within 1C.
Hope this helps some.
Thanks for the feedback
1.) I didn't use the accuracy of the gage blocks, I will be using actual data values given to me at thier last calibration, The uncertainty of measurement reported on the gage blocks was (4.2 + 1.9L) so the SU there was 23.2 uIn on my 10 inch block (worst case unc)
2. and 3.) Thanks, I will be making the recommended changes.
4.) Most likely scenario is it stay in the lab. If my customer has the demand and the money, My hands would be tied by my management forcing us into the field with it. That being said, Temperature correction values? This is what I've found so far:
-ASME/ANSI Y14.5M 1.4(k) states all temperature correction factors should be referenced to 20 C.
-ASME B89.1.9 states the CTE of gage blocks should be between 10.5 and 12.5. (No uncertainty associated with these values)
AISI 1050 steel has a stated of 11.5 between 15 and 25 degrees C.
AISI 52100 steel is stated at 10.5 between 19 and 21.
With all of that, What number do I assign to my blocks for expansion values and is and auditor/assessor going to nitpick the value I assign. I see some labs using 9.5 and some as high as 13.5.
I have mitutoyo grade 2 blocks, I contacted mitutoyo and they claimed all thier blocks manufactorerd during the period of time mine where conformed to AISI 1050 Steel within 90 percent of thier material. Do I take the 11.5 stated and add 10 ucertainty to the value?
Also using the Veriteq Spectrum as a lab temperature monitor, It has a stated accuracy of + or - 1 degree, Should I include this in my budget as a possible 2 degree swing in lab temp due to the unknown of my tempurate monitor? Or will the auditor not even bother with that much information?
Thanks again Jfgunn, And if anybody else can provide insight with the temp correction factors, Please educate me.