Standard accuracy/uncertainty

[Xrayvissle]

I have a serious question.  Anyone in quality position can assist with the answer as well as techs that have some knowledge in it.  It's just something boggling my mind.  Say you have UUT that outputs voltage and you have to input current.  You measure the current output with a valid standard thats more accurate than the current in use. Is the accuracy of the current before measurement neccesary for the calculation of the UUT accuracy? I just want an opinoin from a second, third or however many can give an answer.  Secondly, Why?

[OlDave]

OK, one question.

If you input 5mA into the UUT will your output voltage be different than if you input 20mA? If so, then the input current value and accuracy makes a difference and will need to be included in your uncertainty analysis.

Why? See above....

[Mike]

Maybe

If I understand your question correctly...

You are setting up your input current using a more accurate standard before applying it to the UUT. 

The loading of the UUT and the Standard may affect the current source differently...so if it has a "Constant Current" spec under different loads...like a power supply...then you would probably need to include that...but, the actual current accuracy of the current source would probably not need to be included.

Again, not sure if I got your question right...

[beadwork]

I would include it in your Uc budget.   If it's small enought it won't really make much difference in the budget outcome but including it shows that you considered it.   Usually the UUT resolution is the biggest contributor to the Uc budget.

Uc budgets are always improving as you gain more experience.   That's why they are to be reviewed periodically.

Sincerely,

Mike Boothe (USMC)
Quality Manager, ASQ CCT
Cal Lab Co. , Inc.
www. callabco. com

[Xrayvissle]

Thanks, and yes you got the question on the nose Mike.  I need to recheck my UUT's then. 

[scottbp]

Uc budgets are always improving as you gain more experience.   That's why they are to be reviewed periodically.

Yeah, the funny thing about uncertanties is the more you understand them, the bigger they get!