Calibration-paradigm of conformity

Boris Katz, Metrology consultant, Netanya, Israel (BORISKATZ123@GMAIL.COM)
Guy Katz, Israel, Netanya, Gk Calibration

XXV Annual Meeting of the Israel Analytical Chemistry Society

January 14-15, 2025, Tel Aviv, Israel

 

Calibration-paradigm of conformity

 

Boris Katz ^a, Guy Katz ^b

 

^a Metrology Consulting, Netanya, Israel, email address: boriskatz123@gmail.com

^b GK Calibration, Netanya, Israel, email address: gkatz1@gmail.com

 

Abstract - In general, calibration certificate includes the nominal value of measurand, measured value, measurement error, measurement permissible error (MPE) and measurement uncertainty (MU). Naturally, the last step of calibration process obliges to take into account ratio between MPE and MU, and to define the decision rule of conformity of calibrated item. Guide ILAC G8-2019 "Guidelines on Dcision Rules and Statements of Conformity" provide suggestions for decision rules when considering measurement uncertainty in determining conformance to specifications (MPE). Applying these guidelines can assist businesses in avoiding disagreements with customers and suppliers about conformance to specifications and in managing costs associated with conformance decisions. It is clear that some laboratories, their personnel and their customers may be required to improve their knowledge related to decision rule risks and associated statistics.

For an adequate understanding of the probleme guidelines provide terminology and specify the content that must be addressed when stating a decision rule used for deciding the acceptance or rejection of a product according to specification:

 

• 
  Decision rule- a documented rule, that describes how measurement uncertainty will be allocated regard accepting or rejecting a product according to its specification and the result of a measurement.


• 
  Binary decision rule- a decision rule with only two possible outcomes, either acceptance or rejection


• 
  Specification zone (of an instrument or workpiece)-the set of values of a characteristic between, and including the specification limits


• 
  N:1 decision rule- a situation where the width of the specification zone is at least N times larger than the uncertainty interval for the measurement result


• 
  Acceptance zone-  the set of values of a characteristic, for a specified measurement process and decision rule,

that results in product acceptance when a measurement result is within this zone

• 
  Rejection zone: the set of values of a characteristic, for a specified measurement process and decision rule, that results in product rejection when a measurement result is within this zone


• 
  Guard band - the magnitude of the offset from the specification limit to the acceptance or rejection zone boundary


• 
  Simple acceptance: the situation when the acceptance zone equals and is identical to the specification zone.


• 
  Simple rejection- the situation when the rejection zone consists of all values of the characteristic outside the specification zone.


• 
  Stringent acceptance- the situation when the acceptance zone is reduced from the specification zone by a guard band.

 

Using different statistical approaches, the guide provides opportunities for informed choice of decision rules.

 

 

Keywords: calibration, measurement error, permissible measurement error, measurement uncertainty, conformity, decision rule

 

 

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Short Biography of Presenting Author

1992-2000 The calibration laboratory of Standard Institution of Israel

2000-2008 Accredited calibration laboratory Quality Control Center Hazorea

2008-2017 Accredited calibration laboratory PK Labs

20017-Metrology consulting