Fluke Digital Multimeter Calibration Manual

©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 1

Applying Measurement Uncertainty To

Digital Multimeter Calibration

An introductory study of measurement

uncertainty and its application to digital

multimeter calibration

Teleconference:

US & Canada Toll Free Dial-In Number: 1-[phone]

International Dial-In Number:[phone]

Conference Code: 1010759559

©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 2

Welcome

Greetings from –
Fluke Corporation

Everett, Washington, USA
We are very pleased to bring you this

presentation on measurement

uncertainty for DMM Calibration.

©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 3

Welcome

This presentation is based on Fluke’s

extensive experience with:

− Use and design of calibration
Instruments

− Our experience and understanding of the
problems faced when applying
measurement uncertainty for both
regular and accredited metrology

Thanks for your time, we hope you find it
both valuable and useful.

Welcome and Thanks!

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Presented by

Fluke’s Calibration Business Unit

and Jack Somppi

Electrical Calibration Instruments
Product Line Manager

[e-mail]

©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 5

Web seminar etiquette

• Choice of Audio – VOIP or Teleconference

− VOIP receives audio only while teleconference is two way
sound

• Don’t mute your phone if you have background

music enabled

• Use Q&A or chat to send me questions or request
clarification

• There will be an opportunity throughout the

discussion to pause and ask questions.

• You can view the material using either full screen
or multi window methods

©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 6

Applying Measurement Uncertainty To

Digital Multimeter Calibration

An introductory study of measurement

uncertainty and its application to digital

multimeter calibration

©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 7

Objectives

In this session you will -

• Be introduced to the concept of measurement

uncertainty and why it is important

• Observe the basic elements that influence

measurement uncertainty for DMM calibration
applications

• Study a simple but detailed example of calculating

measurement uncertainty

• Consider some benefits of automating measurement

uncertainty calculations

• Receive a variety of references for further research on

this topic

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Benefits

• Introduce measurement uncertainty to

those in calibration/metrology who are
not familiar with it

• Understand why measurement

uncertainty is important for quality
metrology

• Understand measurement uncertainty

with respect to DMM calibration

• Appreciate to the benefits of automation

• Have technical references for more

detailed information

• Obtain copies of this presentation via

email

©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 9

Measurement Uncertainty

& Why It Is Important

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Facts regarding measurement -

• Can you ever measure the true value of
something?

− No, there will always be errors

• How important is this fact?

− Very important, as measurement is never complete
unless you know how good it is!

• How is this taken into account in today’s

calibration & metrology?

− By applying & documenting the measurement uncertainty
process to the tests being done

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Measurement uncertainty in

metrology today…

Measurement errors were not rigorously evaluated in all
cases. Often in industrial labs, accuracy ratio analysis

(referred to as TUR’s or TAR’s or TSR’s) had been frequently

used to evaluate the significance of the calibrator’s errors on

the measurements. Other errors were sometimes ignored.

Individually analyzed, calculated, & documented measurement

uncertainties are more thorough and are required to be

considered - as stated in

− ANSI/ISO/IEC 17025:2005 General Requirements for the
Competence of Testing and Calibration Laboratories

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ISO 17025 –

about measurement uncertainty…

5.4.6 Estimation of uncertainty of
measurement

− 5.4.6.1 A calibration laboratory, or a testing

laboratory performing its own calibrations, shall
have and shall apply a procedure to estimate the

uncertainty of measurement for all calibrations

and types of calibrations.

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… about the sources of

uncertainty…

ISO 17025, Section 5.4.6.3:

− NOTE 1: Sources contributing to the uncertainty

include, but are not necessarily limited to,

• The reference standards and reference

materials used

• Methods and equipment used

• Environmental conditions

• Properties and condition of the item being

tested or calibrated

• Operator

There are many contributors to uncertainty

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ISO 17025, Section 5.10.4

Calibration Certificates shall include …
for the interpretation of calibration results

a. The conditions of the test
b. The uncertainty of measurement &

compliance statements to metrological standards
c. Evidence of traceability
When statements of compliance are made, the

uncertainty of measurement shall be taken into account

…about calibration certificates…

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An example of an accredited

calibration certificate –

“Measurement uncertainties at the

time of test are given in the following

pages, where applicable. They are
calculated in accordance with the
method described in NIST TN1297,

for a confidence level of 95% using a

coverage factor of approximately 2
(K=2).”

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To summarize the importance of

measurement uncertainty….

From the NPL UK - “A Beginner's Guide to

Uncertainty of Measurement”

• Uncertainty of a measurement tells us something about

its quality

• Uncertainty of measurement is the doubt that exists

about the results of any measurement

• For every measurement – even the most careful – there

is always a margin of doubt

• You need to know the uncertainty before you can

decide whether the tolerance is met

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“How is this Measurement Uncertainty

obtained?”

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Properly Calculating Measurement

Uncertainty – a topic often discussed &

debated among metrologists

Initially, there were no standardized

process to quantify measurement

uncertainty….

But a standard technique was agreed

upon & published in October 1993:

ISO Guide 98 - Guide to the

Expression of Uncertainty in
Measurement (a.k.a. GUM)

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In the USA, refer to one of the Guides

relating to expressing of Uncertainty in

Measurement

ANSI/NCSL Z540.2-1997 (R2002) U.S.

Guide to Expression of Uncertainty in
Measurement

http://www.ncsli.org and find it in the store

under NCSLI publications

NIST Technical Note 1297

http://www.physics.nist.gov/Pubs/guidelines/
contents.html

Recommendation:
Refer to the GUMs -

Internationally, many metrology

organizations publish similar GUMs

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Questions?

- about measurement uncertainty

or why it is important

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Measurement Uncertainty &

Calibrating DMMs

A study of applying the GUM to DMM

calibration

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First – lets look at the concept

Our initial look –

• Consider verifying a

precision digital multimeter

• With a hypothetical study

of verifying the DMM’s

measurement performance

at 100 millivolts DC

• Let’s briefly look at what

measurement uncertainty

could be in this case

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Some sources of measurement

“doubt” when verifying a DMM

• The most obvious & significant sources of doubt:

− Inaccuracy of the calibrator’s output value

• 100.0000 mV might actually be 100.0000 mV .0030 mV

− Repeatability or randomness in measurement values from the DMM

• 100.0003 mV, 99.9995 mV, 100.0010 mV, etc.

− Resolution or sensitivity limits on the DMM

• It’s value is ½ the least significant digit,

• in this example it represents 0.05 V

• Many other factors that could also contribute to uncertainty:

− ambient temperature effects, thermal emfs, noise, loading, power line

conditions, etc.

• Consider all factors and include if they significantly contribute to

measurement uncertainty