1. Calibration of Weighing Instruments
Conference Centre, Centurion
August 1st
Denis LOUVEL, MT-SI
Calibration of Weighing Instruments
Measurement Uncertainty

2. Agenda 1 What is the most important? 2 Risk management 3
Uncertainties related to a weighing 4
Physics behind a weighing result 5
Safe Weighing Range 6 7 8 9
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3. Product or balance?
What is the most important the product or the balance?
Do you need a compliant product or a compliant balance?
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4. Product or balance?
What is the most important the product or the balance?
Do you calibrate the balance for the balance?
Do you calibrate the balance for the product?
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5. Product or balance?
What is the most important the product or the balance?
Are you sure that the content of your current calibration certificate helps?
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6. Agenda 1 What is the most important? 2 Risk management 3
Uncertainties related to a weighing 4
Physics behind a weighing result 5
Safe Weighing Range 6 7 8 9
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Click the arrow, press shift key and move top or bottom
For internal use - Confidential

7. Risk management Preferential regime?
We can assess the balance uncertainty since more than 20 years.
Nevertheless, the classic verification for a balance is to compare the error against the maximum permissible error:
Error  Maximum permissible error (MPE)
This assessment is the same as requested by the Legal Metrology
For other measuring instruments (e.g. thermometers) the uncertainty is always taken into account in assessing compliance of the instrument:
Error + Uncertainty  Maximum permissible error (MPE)
It seems that balances are entitled to a preferential regime and can be assessed according to outdated criteria
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8. Risk management Decide what is the best for you
Knowing that a balance has an error smaller than the MPE, that's good.
Knowing the measurement uncertainty is much better.
Ignore uncertainty when you weight the product is risky.
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9. Agenda 1 What is the most important? 2 Risk management 3
Uncertainties related to a weighing 4
Physics behind a weighing result 5
Safe Weighing Range 6 7 8 9
To shift Highlight
Click the arrow, press shift key and move top or bottom
For internal use - Confidential

10. Uncertainties related to a weighing 3 uncertainties, not only 1
3 uncertainties are involved when you are weighing your product:
The uncertainty of the error of indication
The uncertainty of the balance
The uncertainty of the product weighed on the balance
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11. Uncertainty of the error of indication
All these properties contribute to the uncertainty of the error of indication
In the first level, parameters below are taken into account for the de­termi­nation of the uncertainty of the indication error U(EI):
Repeatability of the weighing
Resolution of the balance (at zero and on load)
Load eccentricity
Ambient temperature during calibration (sensi­tivity coefficient of the balance to temperature)
Standards weights (uncertainty + durability)
Basically, every balance has one important nominal property, the so-called readability. Readability accounts for the rounding error of a digital indication. This balance property is not measured but its contribution to the overall measurement uncertainty is given by the number of digits after the comma and thus is a fixed value.
(click)
A digital weighing instrument has four important measurement properties that contribute to the overall measurement uncertainty. These properties are
The sensitivity
The nonlinearity
The eccentricity, or corner load
And the repeatability
These properties are briefly explained in the next slides.
There are other properties besides these four measurement properties and the readability as a nominal property, but only these contribute significantly to the overall measurement uncertainty of the respective weighing system.

12. The accreditation domain
The balance has not only 1 uncertainty, but one per load
The accreditation covers only the uncertainty of the error of indication
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13. Uncertainty of the Balance
All these properties contribute to the balance uncertainty
A second level is necessary to take into account how the balance is used, installed, set:
the use or not of the internal adjustment device
the correction or not of the errors of indication EI
the temperature range in the room where the balance is used
the eccentricity
With these situations, we can define the balance uncertainty from which the user obtains the uncertainty for each weighing he carries out.
Basically, every balance has one important nominal property, the so-called readability. Readability accounts for the rounding error of a digital indication. This balance property is not measured but its contribution to the overall measurement uncertainty is given by the number of digits after the comma and thus is a fixed value.
(click)
A digital weighing instrument has four important measurement properties that contribute to the overall measurement uncertainty. These properties are
The sensitivity
The nonlinearity
The eccentricity, or corner load
And the repeatability
These properties are briefly explained in the next slides.
There are other properties besides these four measurement properties and the readability as a nominal property, but only these contribute significantly to the overall measurement uncertainty of the respective weighing system.

14. The accreditation domain No information for u(IP)
The accreditation covers only the uncertainty of the error of indication
The accreditation never covers the uncertainty of the balance
For internal use - Confidential

15. Uncertainty of the weighing of the final product
All these properties contribute to the balance uncertainty
A last level is necessary to finally know the influence of the balance on the product:
the uncertainty of the balance
the correction or not of the buoyancy effect
With this information, we can finally assess the product conformity.
Basically, every balance has one important nominal property, the so-called readability. Readability accounts for the rounding error of a digital indication. This balance property is not measured but its contribution to the overall measurement uncertainty is given by the number of digits after the comma and thus is a fixed value.
(click)
A digital weighing instrument has four important measurement properties that contribute to the overall measurement uncertainty. These properties are
The sensitivity
The nonlinearity
The eccentricity, or corner load
And the repeatability
These properties are briefly explained in the next slides.
There are other properties besides these four measurement properties and the readability as a nominal property, but only these contribute significantly to the overall measurement uncertainty of the respective weighing system.

16. The accreditation domain No information
The accreditation covers the uncertainty of the error of indication
The accreditation never covers the uncertainty of the balance
The accreditation doesn't help you to calculate the buoyancy effect (ncpa) and the uncertainty of the weighing result, U(M)
For internal use - Confidential

17. Agenda 1 What is the most important? 2 Risk management 3
Uncertainties related to a weighing 4
Physics behind a weighing result 5
Safe Weighing Range 6 7 8 9
To shift Highlight
Click the arrow, press shift key and move top or bottom
For internal use - Confidential

18. Physics Behind A Weighing Result
The balance is adjusted / verified / calibrated with weights and provides indications as if the weighed object has a density identical to the weights
All balance users know the buoyancy effect (Archimedes' principle), but none of them applies a correction.
They all think that the weight displayed by the balance is the true mass of the object and no correction is necessary.
Unfortunately, this is totally wrong and this can question the quality of the weighing result.
When balance is adjusted with standard weights, both equilibriums carried out to weigh an object (at zero and on load), leads to the following relation:
𝑀×(1 –𝑎/𝑟)=(𝑥–𝐸𝐼)×(1–𝑎/𝑟0)
Users of balances do not apply a correction related to the buoyancy effect.
The correction is not necessary as long as it doesn't jeopardize the compliance of the product.
Before to decide to neglect the correction, it is necessary to know it.
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19. Air Buoyancy Effect It may be neglected
The relative air buoyancy decreases when the density of the object increases.
Close to 8,000 kg/m3, it becomes null and becomes negative for greater densities.
According your weighing requirement, decide if a correction is necessary or not.
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20. Agenda 1 What is the most important? 2 Risk management 3
Uncertainties related to a weighing 4
Physics behind a weighing result 5
Safe Weighing Range 6 7 8 9
To shift Highlight
Click the arrow, press shift key and move top or bottom
For internal use - Confidential

21. Calibrate the process, not the balance
Contact Microsep about the safe weighing range of your balance
The uncertainty of the balance should be used at least to define the safe weighing range
Make sure that your balance is suitable for your process
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22. Thank you for your attention
Visit us on stand to see our solutions to evaluate the Risk Management with Minimum Weight