Metrology Monday! #50 Introduction to and practical guidance on Sensitivity Coefficients
Happy New Year Metrology Mavericks!
I am resuming our discussion about measurement uncertainty and today’s topic is about sensitivity coefficients.? A Sensitivity Coefficient provides information on how sensitive the measurand is to a change in any input quantity.? The simplest example of a sensitivity coefficient is when the measurand is the quantity indicated on a DMM display and the input is the value that the calibrator is set to.?
If we were to increase the output of the calibrator by 1%, the indicated reading on the DMM would increase by 1%, so in this case the sensitivity coefficient is one.? The good news is that for most of your calibrations, the sensitivity coefficient will be one.
The formal definition of the sensitivity coefficient is the partial derivative of the defining equation with respect to the variable (input quantity) in question.? Recall that an equation for power is:
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?If we wanted to understand what the sensitivity coefficient for current was in this equation, the partial derivative with respect to current is:
Each component of uncertainty needs to be multiplied by its sensitivity coefficient before uncertainty components are combined.
If you are not strong in calculus, there are tools out on the internet that will do most of this work for you.? If you just don’t have time to learn how to use them, you can approximate the value for the sensitivity coefficient by increasing or decreasing the value out of calibrator or whatever is your input quantity and observing how much relative change your indicated value changes.? Be sure to do this as a percentage of the original value for both the input and indicated value.
Do you want to accelerate your metrology education, but are worried that the training will be over your head?? Check out the NCSLI Technical Exchange.? This is a special event that is organized by NCSLI to provide technician level instruction on various metrology topics.? It will be held on January 22 to 24 2024 in New Orleans Louisiana!? In particular you should catch Fluke Metrologists Frank Liebmann and his Thermodynamics Tutorial, Michael Johnston doing his tutorial on Understanding Instrument Specifications, Mike Coleman presenting Temperature Calibration Best Practices, or Rong Ding’s tutorial on fixed point cell theory, realization and usage.? You still have plenty of time to register! Check out the other tutorials as well #MetrologyMonday #FlukeMetrology
instructor Emeritis at Ridgewater College
1 年Thx
Especialista en Gerencia de Calidad, Ingeniero Mecánico
1 年Interesting post
Founder @ METROTEKA calibration lab and LORISQ lab equipment management app. Current president of the Croatian Metrology Society. Generally, I like to improve things.
1 年When I began calculating calibration uncertainties many years ago, I did not have the patience to do it - to calculate all the sensitivity coefficients "by the book". That was because after studying physics, I just had a different approach about it. Or so I thought. It took me 10 years to understand I am actually using sensitivity coefficients all along, and that my "intuitive" results were identical to those "by the book".
Love the name of Metrology Mavericks! :)