Calibration & Testing Who, what, where ? Steve Sidney & John Wilson
Agenda So you want to do your own calibrations Definitions – Calibration, Testing etc. What is required in SANAS TR25-02 Practically, what does it mean? Where is the line between calibration and testing?
Introduction Testing Labs regularly send their standards to calibration labs to be calibrated The process of the “contract review” is often poor or not done at all This leads to the results from the Calibration laboratory being unclear or unfit for purpose
Introduction There is also a feeling that the testing labs should be able to calibrate their own standards This presentation will look at the definitions of the measurement system and then investigate what is required to do calibrations This will allow Testing labs to understand what would be required of them if they are to “calibrate their own standards”
Definitions Calibration (from VIM3) operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication
Definitions Calibration (from VIM3) Continued NOTE 1 A calibration may be expressed by a statement, calibration function, calibration diagram, calibration curve, or calibration table. In some cases, it may consist of an additive or multiplicative correction of the indication with associated measurement uncertainty. NOTE 2 Calibration should not be confused with adjustment of a measuring system, often mistakenly called “self-calibration”, nor with verification of calibration.
Definitions Calibration (from VIM3) Continued NOTE 3 Often, the first step alone in the above definition is perceived as being calibration.
Definitions Calibration (simple English) Make measurements (often by comparison) Assign a value Calculate and express an uncertainty (related to the assigned value)
Definitions Testing Not defined in the VIM !!!! However, Verification is defined ! They are basically the same thing
Definitions Verification (from VIM3) provision of objective evidence that a given item fulfils specified requirements EXAMPLE 1 Confirmation that a given reference material as claimed is homogeneous for the quantity value and measurement procedure concerned, down to a measurement portion having a mass of 10 mg. EXAMPLE 2 Confirmation that performance properties or legal requirements of a measuring system are achieved.
Definitions Verification (from VIM3) Continued EXAMPLE 3 Confirmation that a target measurement uncertainty can be met. NOTE 1 When applicable, measurement uncertainty should be taken into consideration. NOTE 2 The item may be, e.g. a process, measurement procedure, material, compound, or measuring system.
Definitions Verification (from VIM3) Continued NOTE 3 The specified requirements may be, e.g. that a manufacturer's specifications are met. NOTE 4 Verification in legal metrology, as defined in VIML, and in conformity assessment in general, pertains to the examination and marking and/or issuing of a verification certificate for a measuring system.
Definitions Verification (from VIM3) Continued NOTE 5 Verification should not be confused with calibration. Not every verification is a validation. NOTE 6 In chemistry, verification of the identity of the entity involved, or of activity, requires a description of the structure or properties of that entity or activity.
Definitions Verification (simple English) Make a measurement Assign a value Uncertainty still needs to be calculated and applied to make sure that the value Uncertainty is still within the required limits Check the value is within the required limits of the specification, regulation etc.
Summary In simple English Calibration Make Measurements Assign a value Calculate and express and uncertainty associated with the assigned value Verification (Testing) Make Measurements Assign a value Calculate an uncertainty associated with the assigned value Check that the assigned value (with the uncertainty) is within the prescribed limits, specification or regulation
Definitions Procedure (from VIM3) measurement procedure detailed description of a measurement according to one or more measurement principles and to a given measurement method, based on a measurement model and including any calculation to obtain a measurement result NOTE 1 A measurement procedure is usually documented in sufficient detail to enable an operator to perform a measurement.
Definitions Procedure (from VIM3) measurement procedure continued NOTE 1 A measurement procedure is usually documented in sufficient detail to enable an operator to perform a measurement. NOTE 2 A measurement procedure can include a statement concerning a target measurement uncertainty. NOTE 3 A measurement procedure is sometimes called a standard operating procedure, abbreviated SOP.
Definitions Validation (from VIM3) validation verification, where the specified requirements are adequate for an intended use EXAMPLE A measurement procedure, ordinarily used for the measurement of mass concentration of nitrogen in water, may be validated also for measurement of mass concentration of nitrogen in human serum.
Definitions Validation (in simple English) Check that the procedure is understood by others Check that the procedure repeatedly delivers the same result (within reason) Perform the measurement by another method to see if the same result is obtained Perform the calculation by another method to see if the same result is obtained Etc.
Practical Example A Testing Lab has a calibrated thermometer which it wishes to use as a reference to “calibrate” their other thermometers with. So why not just put them all in a bath and compare the values against each other?
Practical Example What needs to be considered – The accuracy (of the standard vs UUT) – Is it good enough (i.e. is it at least 4 times better than the UUT tolerance?) – Is the standard calibrated with appropriate uncertainties? – Is the standard within it’s calibration interval? – What is the ability of the bath (or similar) to uniformly “transfer” the temperature between the Standard and the UUTs. – What is the ability to read the standard and the UUTs – Etc, etc, etc
Practical Example The SANAS document TR 25-02 – Criteria for performing Calibration and Intermediate checks on equipment used in accredited facilities. The TR tells you it is a Technical Regulatory document That means you “shall” . (not negotiable) In the section related to “In-House” calibrations the document is very clear.
SANAS TR 25-02 Documented calibration procedure Calibration certificate or report (record data) Education & Training Records to demonstrate COMPETENCE of personnel Demonstrate TRACEABILITY Standards and Measuring Instruments shall be calibrated at appropriate intervals and have procedures to establish the calibration intervals
SANAS TR 25-02 Have a procedure (and capability) for the estimation of UNCERTAINTY Is ONLY ACCEPTABLE when the LAB is ACCREDITED for the in-house parameter Intermediate checks are to maintain confidence, they are NOT a substitute for calibrations (and uncertainty estimations are required)
So where to from here? Differentiate between Lab equipment and Lab Standards The Testing lab needs to understand that if it wants to do calibrations, it MUST comply with TR 25 If you are a testing lab, requiring calibrations from a calibration lab, ensure you have a good Contract Review and define clearly what you want
So where to from here? If you are a calibration lab, doing work for a testing lab, ensure you provide clear and useful information in line with the requirements of the Contract Review process. Remember, there is a very fine line between calibration and testing activities – remember the earlier definitions. Both types of laboratories have huge responsibilities and are at the end of the day, on the same side.
References www.bipm.org www.sanas.co.za www.nla.org.za
Discussion/Questions Thank you
Calibration (from VIM3) Continued NOTE 1 A calibration may be expressed by a statement, calibration function, calibration diagram, calibration curve, or calibration table. In some cases, it may consist of an additive or multiplicative correction of the indication with associated measurement uncertainty. NOTE 2 Calibration should not be .
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