Uncertainty Analysis: Understanding Errors in Quantity Measurements

[Henryflycat]

Hey,

I have a question about uncertainty analysis. So my university told me that, usually a quantity has 3 types of errors, reading error, standard deviation (which comes from some repeated measurements of that quantity), and equipment accuracy (which is usually stated on the equipment).

My question is, if I've got these 3 errors, to report the final quantity with X_est +/- X_error, which error should I use for X_error? Some references said I need to do a propagation of all these 3, like the square root of reading_error^2 + accuracy^2 + std_dev^2. Someone said we can ignore the smaller ones, just the take maximum of these 3 errors to be the final error X_error.

Which method is actually the standard way for error analysis? I'm pretty confused.

Thanks a lot.

 

[gleem]

Someone said we can ignore the smaller ones, just the take maximum of these 3 errors to be the final error X_error.

Ignore only if they do not significantly contribute to the overall uncertainty. It would not make a great deal of sense to include errors whose effect is less than the precision of the measure quantity.

 

[Dale]

Someone said we can ignore the smaller ones, just the take maximum of these 3 errors to be the final error X_error.

You can only do this if the largest is much larger than the others.

 

[Dr Transport]

what is your measurement equation?