Measurement Overkill and why “Accuracy” is the Wrong Word – #42

Metrology Podcast

May 20th is a special day – World Metrology Day! Get a bit of history and learn about all things metrology when you join Daniel Bogdanoff, Bob Stern, and Chris Cox in this special Metrology Day electrical engineering podcast!

App note mentioned by Bob: https://bit.ly/DecisionRules

More about Keysight metrology, calibration, and services: https://www.keysight.com/find/metrology

Topics and time tags:

0:00 World metrology day, and a brief history of the meter and the ohm

2:00 Keysight University has FREE test gear courses!

2:45 Bob Stern, Keysight Metrologist Chris Cox, Keysight Regional Metrologist

4:30 Why does metrology matter? How does it impact us? The global economy relies on a consistency of measurement and test, which is why metrology is important. It allows measurements made in one country to be used and replicated in other countries.

7:25 Metrology and measurement traceability is important. An unbroken chain of traceability is one of the key components of metrology and calibration. It’s a bit like a game of telephone leading back to SI units.

10:00 Keysight DMMs get calibrated off the first commercially available Josephson Junction – a tool that uses quantum physics to provide a very stable voltage.

11:16 Accuracy vs. Measurement Uncertainty A production engineer might say “accuracy” but really it’s all about “measurement uncertainty” Vocabulary of international metrology (VIM): https://www.bipm.org/en/publications/guides/vim.html

12:15 A practical example of how different instruments have different levels of uncertainty

13:45 What’s the significance of measurement uncertainty for a user of test gear or a production engineer?

15:33 The internal adjustments that the factory makes to an instrument are some of the most closely guarded intellectual property / trade secrets.

18:15 The Army uses mobile Josephson junctions to test the DMMs used in Apache helicopter field testing.

18:45 Metrology overkills – times when people went overboard with their measurement uncertainty

21:10 How do you quantify measurement uncertainty? There’s “test uncertainty ratio” which uses your expanded measurement uncertainty.

23:00 You can also get to percent risk, which is easy to wrap your head around. Bob Stern and Chris Cox authored some papers on this topic.

24:00 Why do people make measurements in the first place? There are no perfect measurements

26:45 Metrology in the government/military vs. private sector

29:00 There are a lot of factors for metrology equipment calibration and the engineering metrology equipment. There are different “levels” of calibration and different depth of reporting