The Cove Business Standards Discussion Forums More Free Files Forum Discussion Thread Post Attachments Listing Cove Discussion Forums Main Page
UL - Underwriters Laboratories - Health Sciences
Go Back   The Elsmar Cove Business Systems and Standards Discussion Forums > Common Quality Assurance Processes and Tools > General Metrology, Measurement Device, Calibration and Test Laboratories > Measurement Uncertainty (MU)
Forum Username

Elsmar Cove Forum Visitor Notice(s)

Wooden Line

Weight Calibration Uncertainty

Elsmar XML RSS Feed
Elsmar Cove Forum RSS Feed

Monitor the Elsmar Forum
Sponsor Links

Courtesy Quick Links

Links that Cove visitors will find useful in your quest for knowledge:

International Standards Bodies - World Wide Standards Bodies

ASQ - American Society for Quality

International Standards Organization - ISO Standards and Information

International Quality Services

Marcelo Antunes'
SQR Consulting, and
Medical Devices Expert Forum

Bob Doering
Bob Doering's Blogs and,
Correct SPC - Precision Machining

Ajit Basrur
Claritas Consulting, LLC

NIST's Engineering Statistics Handbook

IRCA - International Register of Certified Auditors

SAE - Society of Automotive Engineers

Quality Digest

IEST - Institute of Environmental Sciences and Technology

Thread Tools Search this Thread Rating: Thread Rating: 1 votes, 5.00 average. Display Modes
  Post Number #1  
Old 12th June 2001, 04:20 PM

Total Posts: n/a
Screw Weight Calibration Uncertainty

Our calibration lab has initiated uncertainty measurements of weight standards.
They are responsible for calibrating around 60 different weight sets (around 25 weights per weight set) and around 200 individual weights.

They just showed me what they were doing to calculate uncertainty -- it looked close and might be OK -- but I thought I'd check to see what more experienced people thought.

They calculated uncertainty based on the uncertainty of the lab standard weight and the standard deviation of three reps of ABBA sequences (A= standard ; B= unknown). THey calculated a standard deviation based on six differences (A's - the adjacent B's).

Is this OK -- or would it be better to pool the standard deviation from like weight calibrations? THey have no historical data.

Sponsored Links
  Post Number #2  
Old 13th June 2001, 08:19 AM

Total Posts: n/a
How did they "calculate" the uncertainty? How are the measurements being performed? What is the resolution of any instruments? Are instruments analog or digital? What are the uncertainties of all of the components of the measuring system?
Sponsored Links

  Post Number #3  
Old 13th June 2001, 08:57 AM

Total Posts: n/a
Thank you very much for your response. The balance that is used is digital. It is considered to be the "Standard" balance for weight calibrations. For a given weight calibration, the same balance is always used, i.e., for all 1 gram weights, a particular Mettler or Sartorius balance is used.

Calculations at this point are based on three repeats of six comparisons of working standard to lab standard. Here's an example of the data

A 0.99997
B 1.00015
B 1.00021
A 0.99998
A 0.99995
B 1.00020
B 1.00019
A 0.99987
A 0.99993
B 1.00019
B 1.00014
A 0.99991
A&B DIFF 0.00024

MEAN A 0.99994
MEAN B 1.00018

Uncertainty was calculated by determining the standard deviation of the lab standard's weight (not the uncertainty of the differences between the lab standard and the reference) and combining that with the standard deviation of the reference.

I see referenced in EA-4/02 that the difference within each ABBA grouping should be considered a single observation. If I directed the lab in that direction, there would only be three observations. Since they calibrate many similar sets of weights to the same reference, can I pool the standard deviations from similar comparisons (e.g., all similar 1 gram weight references)?

Sorry this is so long, I really appreciate comments and responses that I have gotten.
  Post Number #4  
Old 14th June 2001, 10:27 AM

Total Posts: n/a
I'll give you some of the details of a 1 gram analysis I just did.

Subject unit is a class F 1 gram mass.

Measurement parameter is 1 gram reference mass calibrated with a stated uncertainty of 0.01832 mg from the calibration source.

five readings on the class F mass yield standard deviation of .005 mg at 95.0 confidence level.

next I use uncertainty=(xmass*(1-(air density/ref mass density)))/(1-(air density/mass density\))-.001

combining these values gives uncertainty of .018mg with infinite degrees of freedom.

root sum square of the component uncertainties give combined uncertainty of .0259mg at 95% confidience level and 348 degrees of freedom.

Hope this helps

  Post Number #5  
Old 14th June 2001, 11:26 AM

Total Posts: 944
Try downloading the freeware proficiency calculator from It is in the downloads section. There are examples for mass and scale calibration, along with many others. It was very useful on a recent 17025 audit for a scale calibration company I consulted for.

Hope this helps,


Last edited by howste; 1st November 2009 at 03:09 AM. Reason: fixed URL
  Post Number #6  
Old 14th June 2001, 03:09 PM

Total Posts: n/a

I downloaded the software -- looks real good.
I have a few things to figure out -- (I'm referring to the UC mass 10 kg nominal.unc file. For example 'comparator linearity'.

This example and the replay from Greg have helped me a lot. We were initially going to ignore boyancy -- but I can see that I need to take that into account.

I'm sure we will be using this software. I like that examples are included.

  Post Number #7  
Old 14th June 2001, 03:13 PM

Total Posts: n/a

Thanks for your help. I've looked up a lot of information on boyancy -- I see that I can't ignore it. I'll have to go down to the lab and check out conditions to figure out the air density. I already know temperature and humidity.

I really appreciate you taking the time to review the information in my post and reply.

Thanks again.

  Post Number #8  
Old 14th June 2001, 03:58 PM

Total Posts: 944
You might be able to get more help from your state department of weights and measures. In Michigan, the Dept. of Agriculture certifies most of the calibration standards in use by scale companies. They might be more willing to help than a commercial lab. I found a link to all of the different state departments here:

*** Dead Link Removed ***

You can try

Lower Navigation Bar
Go Back   The Elsmar Cove Business Systems and Standards Discussion Forums > Common Quality Assurance Processes and Tools > General Metrology, Measurement Device, Calibration and Test Laboratories > Measurement Uncertainty (MU)


Visitors Currently Viewing this Thread: 1 (0 Registered Visitors (Members) and 1 Unregistered Guest Visitors)
Thread Tools Search this Thread
Search this Thread:

Advanced Forum Search
Display Modes Rate Thread Content
Rate Thread Content:

Forum Posting Settings
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Similar Discussion Threads
Discussion Thread Title Thread Starter Forum Replies Last Post or Poll Vote
Weight Calibration Standards - External Calibration Frequency smryan General Measurement Device and Calibration Topics 11 29th December 2013 09:45 PM
Calibration Reference Standard for Mass Weight Calibration FIRAS_N General Measurement Device and Calibration Topics 2 7th August 2012 02:07 AM
Determining Calibration Uncertainty with Unknown Reference Standard Uncertainty howste Measurement Uncertainty (MU) 8 18th February 2011 04:34 PM
A little weight on my mind for New Year's - Measurement Uncertainty ScottBP Measurement Uncertainty (MU) 3 12th January 2009 01:47 PM
Weight Measurement Uncertainty - F1 10 Kg weight comparison with 10 Kg E2 weight ahmadfy2003 Measurement Uncertainty (MU) 4 5th January 2007 03:30 PM

The time now is 03:45 PM. All times are GMT -4.
Your time zone can be changed in your UserCP --> Options.


NOTE: This forum uses "Cookies"