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Hi
I was just going through some old threads on calibration accuracies. Some very good info, but I'm still confused as to how one should spec a calibration accuracy requirement.
Suppose you need to measure a spec of say +/-0.002" (total tolerance = 0.004"), then my understanding from prior threads is that:
1) I should use a piece of eqpt that has resolution of at least 0.0004" (10:1 rule of thumb)
2) I should calibrate using a standard that is at least 4 times more accurate than the accuracy I want (4:1 rule of thumb)
But how do I decide on the accuracy needed?
From looking at previous threads, a common answer seems to be that I need to calibrate to an accuracy of 1/4 the tolerance (i.e. 0.001"). I find it hard to believe that the 4:1 rule is intended to be used like this - 0.001" just seems way too crude. As I understand it, the 4:1 rule refers to the accuracy of the standard relative to that of the equipment, not the equipment relative to the spec.??
Anyways, my question is would anyone know how would you go about specifying a calibration accuracy for the equipment in this case?
Thanks
I was just going through some old threads on calibration accuracies. Some very good info, but I'm still confused as to how one should spec a calibration accuracy requirement.
Suppose you need to measure a spec of say +/-0.002" (total tolerance = 0.004"), then my understanding from prior threads is that:
1) I should use a piece of eqpt that has resolution of at least 0.0004" (10:1 rule of thumb)
2) I should calibrate using a standard that is at least 4 times more accurate than the accuracy I want (4:1 rule of thumb)
But how do I decide on the accuracy needed?
From looking at previous threads, a common answer seems to be that I need to calibrate to an accuracy of 1/4 the tolerance (i.e. 0.001"). I find it hard to believe that the 4:1 rule is intended to be used like this - 0.001" just seems way too crude. As I understand it, the 4:1 rule refers to the accuracy of the standard relative to that of the equipment, not the equipment relative to the spec.??
Anyways, my question is would anyone know how would you go about specifying a calibration accuracy for the equipment in this case?
Thanks
