Calibration Standards
Calibration Standards
(OP)
I am looking for a standard calibration deviation tolerance.
i.e. if you have .010 ±.005 given to the machinist to cut. What will the + percentage be for some one to calibrate to, and is there such a thing?
i.e. if you have .010 ±.005 given to the machinist to cut. What will the + percentage be for some one to calibrate to, and is there such a thing?





RE: Calibration Standards
Years ago a 10:1 factor was used. But it was expensive. Now-a-days a 4:1 ratio is prefered. Per your example of .010" +/- .005" The tolerance of .005" is divided by 4. Therefore your calibrating instrument myst be accurate to .00125 or better.
RE: Calibration Standards
Thanks
Scott Cobb
CSM Manufacturing, Inc
csm-mfg.com
RE: Calibration Standards
"...the collective uncertainty of the measurement standards shall not exceed 25 percent of the acceptable tolerance for each characteristic being calibrated. ..."
Note that this is somewhat tighter than what one might reasonably do with RSS'ing of the component tolerances, since the words imply a simple arithmetic sum of the tolerances. Usually, though, most customers accept the argument for RSS'ing of the tolerances.
TTFN
RE: Calibration Standards
MIL-HDBK-52B Evaluation of Contractor's Calibration System, paragraph 5.1 Calibration system requirements, states:
"...This is commonly called a 4:1 test accuracy ratio..."
Likewise MIL-HDBK-1839A Handbook Calibration and Measurement Requirements, paragraph 5.4.3 Test Uncertainty Ratio, states:
"The recommended TMDE shall be capable of measuring or generating to a higher accuracy than the measurement parameters being supported. Unless otherwise specified, a minimum TUR of 4 to 1 is desired. The actual TUR shall be documented."
TTFN
RE: Calibration Standards
RE: Calibration Standards
Therefore, the NIST standard could be as much as 4x4x4=64 times smaller tolerance than anything you're actually measuring.
For linear distances, the above is quite easily obtainable, since distance measurement is reasonably accurate down to the submicrometer level. In other areas, 1% relative accuracy is pretty darn good.
TTFN
RE: Calibration Standards
RE: Calibration Standards
TTFN
RE: Calibration Standards
RE: Calibration Standards
"The error attributable to calibration should be as small as possible. In most areas of measurement, it should be no more than one third and preferrably one tenth of the permissible error of the confirmed equipment."
TTFN
RE: Calibration Standards
Thanks
SMR
RE: Calibration Standards
TTFN