# Absolute to Relative Uncertainty - Expressing the U as a percent of the reading

E

#### edge540

I am working on my uncertainty budget for a 1m long calibration device for testing machine crosshead travel and long stroke extensometers. Basically I want to express the U as a percent of reading. So far everything is absolute in um... so I'm a bit stuck.

I have had the instrument calibrated and they give a +/- 5um uncertainty to the device.
Resolution is 1um.

I calculated through a repeatability study appx 15um for the std dev. and then introduced a cosine error and came up with appx 23um for that std. dev.

In the end I calculate about a 27um Uncertainty... but I would rather express it as a % of reading.
I'm not too clear on how to do that though.

If this question has been asked (and it is probably buried here somewhere) I apologize in advance.

Any help is appreciated.

#### Stijloor

Staff member
Super Moderator
I am working on my uncertainty budget for a 1m long calibration device for testing machine crosshead travel and long stroke extensometers. Basically I want to express the U as a percent of reading. So far everything is absolute in um... so I'm a bit stuck.

I have had the instrument calibrated and they give a +/- 5um uncertainty to the device.
Resolution is 1um.

I calculated through a repeatability study appx 15um for the std dev. and then introduced a cosine error and came up with appx 23um for that std. dev.

In the end I calculate about a 27um Uncertainty... but I would rather express it as a % of reading.
I'm not too clear on how to do that though.

If this question has been asked (and it is probably buried here somewhere) I apologize in advance.

Any help is appreciated.
Any calibration/uncertainty experts who can help?

Thank you!

Stijloor.

M

#### Mike Boothe

Convert each item in your uncertainty budget to % of reading then your result will be in % of reading.

E

#### edge540

Convert each item in your uncertainty budget to % of reading then your result will be in % of reading.
Yes, I was thinking about it last night and decided to do that.

I have 10 set points and ten readings each but its in excel now so it should be easy to take care of that.

Should I then combine all to use in my Type A uncertainties or should I take each one individually in there?

Once in % I suppose I only need to take the Std Dev of all and use one Type A.

What about resolution? it is abs. 0.001mm
And the calibration report UnC is 0.005mm (the range will be 50mm to 999mm)
Should I use the 50mm point for those (since they are the worst case so to speak)

Resolution is then 0.002% and the Cal Cert Unc is then 0.01% (k=2)

Does that make sense? (that is the one question that I remember from my Uncertainty training course back about 10 years ago,,, problem is that some of this makes sense but I'm not so sure I know if that is me wanting for it to make sense or if it really does)

D

#### dv8shane

What about resolution? it is abs. 0.001mm
And the calibration report UnC is 0.005mm (the range will be 50mm to 999mm)
Should I use the 50mm point for those (since they are the worst case so to speak)

Resolution is then 0.002% and the Cal Cert Unc is then 0.01% (k=2)
Using the worst case is in my opinion OK but not preferred, as the customer will inherit your transfer uncertainty. Therefore at the points where your uncertainty is much better you are providing a lesser service to them.

I think the resolution contribution is lower than stated as the distribution of resolution is determined at a 100% level of confidence by dividing by root 12.
Question Do you also include degrees of freedom in your budgets?

Last edited by a moderator:
E

#### edge540

I do field service and am pretty conservative with my budgets. In this case, the parameter need not be super critical so I would rather take a higher uncertainty as I know that there will be setup issues and other contributors in reality once this is in service.

In I do use DOF in my calculations (normally using the Unc 3.2 calculator).

Thread starter Similar threads Forum Replies Date
Absolute Interval measurement of CTS/CSE Waveforms IEC 60601 - Medical Electrical Equipment Safety Standards Series 0
N Understanding the absolute uncertainty specification for a Fluke 5500A Measurement Uncertainty (MU) 3
Training the absolute beginner to understand AQL Training - Internal, External, Online and Distance Learning 1
Pressure Calibration to psiA (psi Absolute) General Measurement Device and Calibration Topics 8
9 ANSI Y14.5M Absolute Limits and Measurement question Various Other Specifications, Standards, and related Requirements 6
How Many Absolute Shalls Are There In ISO 9001:2000? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 25
A What's the absolute minimum requirements/costs? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 12
A PFMEA - Is having the DFMEA An Absolute Requirement when doing a PFMEA FMEA and Control Plans 19
Acceptable maximum RSD (relative standard deviation) for an sample size Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
S Methods to reduce relative humidity in Datacenter IEC 27001 - Information Security Management Systems (ISMS) 3
J Relative Humidity and Plastic Raw Material Moisture Manufacturing and Related Processes 4
E RSD (Relative Standard Deviation) Calculation for two series of numbers Statistical Analysis Tools, Techniques and SPC 4
Definition Brief Period of Time relative to Temperature Excursions for Finished Products Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 1
Relative - "The machine that changed the World" Book, Video, Blog and Web Site Reviews and Recommendations 1
E ASTM E2309-05 Classification Table - Fixed to Relative Errors General Measurement Device and Calibration Topics 5
N Uncertainty calculations for RH (Relative Humidity) sensors Measurement Uncertainty (MU) 5
D Procedures or Quality System relative to a Telecommunication Organization TL 9000 Telecommunications Standard and QuEST 3
A Relative or Combined Type A & Type B Uncertainty Calculation? Measurement Uncertainty (MU) 4
K Relative Humidity Requirement on Calibration Certificates General Measurement Device and Calibration Topics 5
C Interpreting Minitab Gage R&R study results - Relative Crease Strength (RCS) Using Minitab Software 3
A Relative Humidity + ISO 9001:2000 Audit of Maintenance Department ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 30
A How to calculate Relative Uncertainty - Measurements are in different units Measurement Uncertainty (MU) 4
A Does anyone know something about Relative Uncertainity? Measurement Uncertainty (MU) 1
R What relative information should be provided in Monthly QA Reports? Document Control Systems, Procedures, Forms and Templates 11
Convert Dewpoint Temperature specification to RH (Relative Humidity) General Measurement Device and Calibration Topics 2
How Big is a Micron? Relative sizes graphic for visual contrast General Measurement Device and Calibration Topics 7
M Relative Elements to Audit General Auditing Discussions 2
D Product Safety - 4.2.3.4 - Safety considerations relative to the supplier's product? QS-9000 - American Automotive Manufacturers Standard 2
Uncertainty not Required Measurement Uncertainty (MU) 3
Should resolution be included in uncertainty budget for digital caliper or micrometer calibration? Measurement Uncertainty (MU) 5
Uncertainty budgets and meeting 4:1 TUR for digital calipers and micrometer Measurement Uncertainty (MU) 0
Measurement Uncertainty in Optical Microscopy Measurement Uncertainty (MU) 1
Uncertainty calculation for an average Measurement Uncertainty (MU) 1
Determining Uncertainty from Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
IEC 60601-2-10 - Accuracy of Pulse Parameters - Required Measurement Uncertainty IEC 60601 - Medical Electrical Equipment Safety Standards Series 3
Missing value of Uncertainty B Measurement Uncertainty (MU) 10
Issues in Uncertainty Estimation Measurement Uncertainty (MU) 5
Operator Manual and Type B Uncertainty Measurement Uncertainty (MU) 3
Learning Uncertainty Budget for Novice - Fluke 5520A Measurement Uncertainty (MU) 1
Does pitch/increment/resolution of a ruled scale apply to measurement uncertainty as line item? Measurement Uncertainty (MU) 10
Uncertainty in measurement larger than tolerance Measurement Uncertainty (MU) 2
Uncertainty Budgets - Phase Noise (SSB), Harmonics Measurement Uncertainty (MU) 2
ISO 17025:2017 clause 7.6.2 - Performing calibration of its own equipment shall evaluate the measurement uncertainty ISO 17025 related Discussions 6
Informational US FDA Final Guidance – Consideration of Uncertainty in Making Benefit-Risk Determinations in Medical Device Premarket Approvals, De Novo Classificati Medical Device and FDA Regulations and Standards News 0
Uncertainty Budget - Externally produced sensor module Measurement Uncertainty (MU) 1
Discussion between co-worker on tolerance and uncertainty and how to apply it. Thoughts? 17025 ISO 17025 related Discussions 1
Assigning a calibration tolerance - An x-y coordinate machine - Uncertainty as my verification tolerance General Measurement Device and Calibration Topics 4
3 Operator Std. Dev. and uncertainty calculation Measurement Uncertainty (MU) 2
Reporting measurement uncertainty for custom items Measurement Uncertainty (MU) 2
L Gage R&R for test precision or uncertainty prediction? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2