Uncertainty

Started by ruebenn, 07-11-2013 -- 08:49:07

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ruebenn

07-11-2013 -- 08:49:07
Greetings.
Hope you guys are in good health.
I have a rather simple question that i would appreciate all the help that i can get .
Say , if we wish to determine the uncertainty equation for R, resistance using the ohm's law - how do we go about it?
I know R = V/I but how do we put it in uncertainty equation inclusive of the sensitivity coefficients added to it as well?
Thank you in advance.
Rgds

RFCAL

#1
07-11-2013 -- 09:03:17
Where did the numbers for R, V, I come from? If you are just talking about Ohm's Law, there would not be a calculable uncertainty for the formula itself.

Hawaii596

#2
07-11-2013 -- 09:24:06
Just guessing, but I would think all three are ratiometric reference points.  They don't so much need numbers as consistency.  Each one is defined as having a relationship to the other two.  The only one with actual numbers I think is the ampere... according to Wikipedia  "In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241 × 10E18 electrons, or one coulomb per second constituting one ampere."  I don't think they knew that number when the three ratiometric values of Ohm's Law was created.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

USMC kalibrater

#3
07-11-2013 -- 15:17:48
 You need to know the uncertainty of V and of I with respect to the value of R you are calculating the measurement uncertainty for.
What type and value resistor/resistance are you measuring, what standards are being used, what type of enviroment are you measuring in, what type of leads are being used what is the uncertainty of the standards etc
Your question is missing to many values for a solid answer
Jason
"Be polite, be professional, but have a plan to kill everybody you meet." -General James Mattis

Hawaii596

#4
07-11-2013 -- 15:30:57
My apologies that in my haste, I missed the fundamental of the question.  Duh.  Long day.   Sorry for the somewhat irrelevant answer.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

griff61

#5
07-14-2013 -- 19:21:46
Quote from: Hawaii596 on 07-11-2013 -- 15:30:57
My apologies that in my haste, I missed the fundamental of the question.  Duh.  Long day.   Sorry for the somewhat irrelevant answer.
Would you say that you were a bit...uncertain?
Sarcasm - Just one more service I offer

Hawaii596

#6
07-15-2013 -- 08:00:07
If I could imitate the voice of one of those little Minions from "Despiccable Me 2" I would reply with "Ooo Ha ha."  (great movie, by the way - for a kids movie).
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

USMCPMEL

#7
07-16-2013 -- 15:42:50
Did you stay all the way till the end and watch the credits??? Also did you watch it in 3-d???

Hawaii596

#8
07-17-2013 -- 08:01:53
I did watch the credits.  I can't remember if I watched 3D (been to a lot of movies lately - and a lot of them in 3D).  Good movie, though.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883
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