Issues in Uncertainty Estimation

fahimk

Involved In Discussions
#1
Folks,

I need your help in tracing the errors and in further refining the Uncertainty Budget (sheet attached).

I wanted to keep it simple and therefore for Type B, I just considered the following three flavors:

UB1= due to calibrator inaccuracy
UB2 = calibration certificate
UB3 = resolution of the UUT

The confusion part: The Uncertainty (UB1) is causing a whooping increase in the final expanded uncertainty calculations.....
(In the Tab UB1, the column V shows the uncertainty after applied the essential coefficients (coverage factor, and the distribution coefficient etc).

Now, how i got it...

1) I got the concept after having a look on the Fluke's webinar: http://download.flukecal.com/pub/literature/webinar-uncertainty-presentation-Dec%202011.pdf (Page 37)

2) Then, i consulted the specification table from the Fluke's Operator Manual http://download.flukecal.com/pub/literature/5520a___omeng0600.pdf (Section: 1-12. Specifications)

I applied the method from (1) on (2) @ 50 Hz and eventually it lead me to the uncertainty in column V.

Can anybody please help me identify the blunder(s) i made?

Thanks a lot in advance...
 

Attachments

Elsmar Forum Sponsor
#2
I am not certain (I'm just learning about making budgets myself), but hasn't the values in UB1 already been factored in the reference standard's uncertainty value? Hopefully someone with more uncertainty budget expertise than myself will chime in on this.
 

dgriffith

Quite Involved in Discussions
#3
I'm at work (playing with your spreadsheet... :geek: ) and I think you should look at your formulas. Example; Line 17 on UB1; S17 references A17, which is empty. Col. O is percent of output. In cell S17 you do math but it doesn't look like you account for the percent in O17. I think it's less confusing to have it as ppm, i.e. 12ppm of output. Then from S17, O17 * A17 (which is now 10V) is 0.000120uV, plus P17/1000000 (which is 20uV).

You now have [email protected]%CL. I'm almost certain this calibrator distribution is Gaussian, not rectangular. Removing the *Sqrt(3) from formula in V17 gets 0.000050, or 50uV.
 
Last edited:

fahimk

Involved In Discussions
#4
I'm at work (playing with your spreadsheet... :geek: ) and I think you should look at your formulas. Example; Line 17 on UB1; S17 references A17, which is empty. Col. O is percent of output. In cell S17 you do math but it doesn't look like you account for the percent in O17. I think it's less confusing to have it as ppm, i.e. 12ppm of output. Then from S17, O17 * A17 (which is now 10V) is 0.000120uV, plus P17/1000000 (which is 20uV).

You now have [email protected]%CL. I'm almost certain this calibrator distribution is Gaussian, not rectangular. Removing the *Sqrt(3) from formula in V17 gets 0.000050, or 50uV.
Thanks mate for the response. I will be reviewing the work thoroughly!

Just a quick question: for writing final standard uncertainty, for category B, am i right if put two numbers in the denominator (one to represent the confidence level and another for the distribution)? Secondly, if no distribution scheme is provided then i should assume a rectangular distribution (i.e. denominator as root of (3)?

Looking forward....
 

Wolf.K

Quite Involved in Discussions
#6
Thanks mate for the response. I will be reviewing the work thoroughly!

(...)

Looking forward....
Hi, could you update your spreadsheet and post it here again? Elsmar is full of alpha version documents, but people unfortunately often forget to post the final result of the discussions here! :)
 
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