The document describes three methods for determining calibration intervals for instruments: the drift method, periodicity ratio method, and OPPERET method. The drift method models wear trends to determine maximum drift and is best for equipment that experiences drift. The periodicity ratio method calculates uncertainty ratios to link interval length to a ratio score. The OPPERET method qualitatively rates criteria like use frequency to assign intervals. The methods are complementary and a company should select the appropriate method for each instrument based on its characteristics.

1. January 2017
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Calibration intervals
FD X 07-014 Methods

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Optimization of calibration intervals
FDX07-014
• Drift method
• Periodicity ratio
• OPPERET method
Three complementary methods proposed by the FDX07-014 for the
management of a set of instruments

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Drift method
Method idea
• Applicable to an equipment that
actually drift
Example : Gauges
• Anticipate date of wear limit by
past behavior
Change in frequency of use of equipment may affect the drift
 Non-monotonic drift  wrong estimate of the wear date
Study the behavior of a set of equipment
12,596
12,595
12,594
12,593
12,592
12,591
12,590 Wear
limit
date

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Drift method
Application of the method
Study:
• Study on a group of similar equipments
• Modeling of the wear trend of each
instrument
• Determination of the case where the
drift is statistically maximum = αmax
Application :
• Next calibration date of each equipment
determined by αmax
12,596
12,595
12,594
12,593
12,592
12,591
12,590 Wear
limit
Last
calibration
α max
date
Next calibration
α max
12,596
12,595
12,594
12,593
12,592
12,591
12,590 Wear
limit
date

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Drift method
• Advantages :
- Specific study for company
- Periodicity technically justified
- Periodicity adapted to each equipment
new ring : Large periodicity – Worn ring : low periodicity
• Disadvantages :
- Method limited to equipments that actually have drift
- Need for a large number of equipment for the statistical study
minimum 20 equipment by category
- Need to know the history of measurement
3 or 2 previous calibrations of the equipment

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Periodicity Ratio
Method idea
Uncertainty in measurement
5M method
uequipment uprocess
Determination of the weight of the equipment in the
uncertainty of the measurement process: uequipment et uprocess
• If uequipment << uprocess
The equipment has little impact
on the measurement process
 LARGE interval
• If uequipment ≈ uprocess
The equipment predominates in
the measurement uncertainty
 SHORT interval
Man
Power
Machine
Milieu
Materials
Method
____________
___
__________
__________
__________
____________
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_______
_______
_______

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Periodicity Ratio
Application of the method
• Definition of Periodicity Ratio
 Quantification of the weight of the equipment in the overall
uncertainty of the measurement process
𝑅 𝑝𝑒𝑟 =
𝑢 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡
2
𝑢 𝑝𝑟𝑜𝑐𝑒𝑠𝑠
2 × 100
Périodicité(an)
Rper (%)
0 20 40 60 80 100
0
2
4
6
8
10
• Determination of periodicity
 Define a link between Rper and periodicity.
Mathematical relationship + hypothesis
Example :
𝑅 𝑝𝑒𝑟 = 0% → 𝑝𝑒𝑟 = 10 𝑦𝑒𝑎𝑟𝑠
𝑅 𝑝𝑒𝑟 = 50% → 𝑝𝑒𝑟 = 1 𝑦𝑒𝑎𝑟
𝑅 𝑝𝑒𝑟 = 100% → 𝑝𝑒𝑟 = 0 𝑦𝑒𝑎𝑟
Periodicity(year)

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Periodicity Ratio
• Advantages :
- Periodicity adapted to the use of the equipment
- Identify the case in which the equipment has a small or a big impact
• Disadvantages :
- Need to evaluate individual uncertainty
- Do not take into account some qualitative parameters
Frequency of use of the equipment, aggressive environment…

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OPPERET method
Method idea
Frequency of use
aggressive
environment
Self-service
equipment
…
Common sense put into equation
Calibration
Interval
The calibration interval intuitively depend on qualitative parameters.
These parameters will help to determine the periodicity

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OPPERET method
Application of the method
• Definitions of evaluation criteria, ratings and weights
base score for an instruments park
• Rating of instruments according to the criteria defined
Example : Criteria -2 0 2
Severity of an erroneous
measurement (3)
Customer Security
Potentially noticed
by the customer
Never noticed
by the
customer
need metrological performance (2)
Weight in the
process
Low impact in the
process
No interaction
in the process
Drift of the equipment and/or
robusness of the equipment (2)
Drift with
consequences
Drift without
consequences
No drift
Number of Aggravating Factors(1) 4 ou + 2 None
cost of calibration (2) Reduced cost Average cost High cost
• Association of a periodicity according to the rating
Calculation made by a mathematical method described in the standard
(n) = weight

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OPPERET method
• Advantages :
- Intuitive principle of the method
Easy to integrate a new equipment into this method
- Suitable method for a wide variety of equipment and uses
- Periodicity adapted to the use of each instrument
Ex : 2 identical devices used differently may have 2 different periodicities
• Disadvantages :
- need of a large number of various equipment (minimum 50)
- setting can be judged long for a park with many equipments
The notation is individual, but quick implementation solutions exist
- Assumptions to be observed when setting up the rating base

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FDX07-014 – Complementary methods
The three methods presented are complementary
It is up to you to associate them correctly to your instruments
according to the different characteristics of the methods
• Drift method:
- Equipment that derives
- Historical of calibration
- Determination the maximum
wear out slope
• Periodicity Ratio:
- Equipment and process uncertainty
- Weight of the equipment in the overall uncertainty
- Link between periodicity and Ratio
• OPPERET :
- Qualitative parameters
- scoring
- lots of different equipments

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