INTERPRETATION OF CALIBRATION REPORTS

Selection of Calibration Agency Calibration Periodicity What is Calibration ? Why Calibrate ? Selection of Calibration Agency Calibration Periodicity Review / Interpretation of a Calibration Report Requirements of ISO 17025 for reporting results Acceptance of Calibrations Reports How we can get updated ?

What is Calibration ? According to the International Organization for Standardization publication entitled International Vocabulary of Basic and General Terms in Metrology, Calibration is the set of operations that establish, under specified conditions, the relationship between values indicated by a measuring instrument, a measuring system or values represented by a material measure, and the corresponding known values of a reference equipment or material

Why Calibrate ? Industries, Research Organizations and Factories worldwide spend millions of dollars annually to calibrate their instrumentation yet the tangible evidence of what has been obtained in return for this investment generally receives inadequate attention

Why Calibrate ? Calibration is accepted as a performance comparison against a standard of known accuracy. Calibration is done, To ensure readings from an instrument are consistent with other measurements. To determine the accuracy of the instrument readings. To establish the reliability of the instrument i.e. that it can be trusted or traceable.

Types of Calibration Accredited Non Accredited In house Calibration

Selection of Calibration Agencies

Calibration Agencies In order to get valid calibration results with global metrology system and to provide globally accepted quality products / services, the selection of the calibration agency is crucial.

Selection of Calibration Agencies

Selection Criteria Calibration Range Sufficient Test Accuracy Ratio Traceability Better Calibration Measurement Capability Availability of Services Regulatory authority /Accreditation agency Requirements Cost of calibration Level /Position required in traceability chain

Calibration Range When considering / selecting a lab for calibration service, it should be thoroughly verified that calibration points at which the UUC has to be calibrated are within the range of Calibrating lab’s scope of service. Eg: For a calibrating a thermometer with a resolution of 1C at 100 C, we have to choose a Calibration Lab with a reference thermometer having a resolution of at least 0.1C and a range of more than 150.00C.

Test Accuracy Ratio In a calibration procedure, the TAR is the ratio of the accuracy tolerance of the unit under calibration to the accuracy tolerance of the calibration standard used. [based on NCSL Glossary of Metrology-related Terms].

Traceability Calibrating Laboratories should establish a chain of traceability through national / international standards. Traceability is a property of the result of a measurement, providing the ability to relate the measurement result to stated references, through an unbroken chain of comparisons each having stated uncertainties.

Calibration Measurement Capability Calibration & Measurement Capability (CMC) is the value of uncertainty assigned by any accreditation body for a calibration laboratory. It is the best uncertainty, that calibration laboratory can provide for any measurement with in the range of a specific parameter Eg with a volume calibration

Calibration Measurement Capability When a pipette has to be calibrated from a accredited calibration laboratory, scope of the lab should be verified whether it meets the requirements in terms of parameter, range and Calibration Measurement Capability (CMC). Requirements : Pipette is having a range of 10µl to 1000 µl with a resolution of 1 µl and an accuracy of ± 8 µl.

Lab 1 Lab 2

Calibration Agencies Comparison Pipette is having a range of 10µl to 1000 µl with a resolution of 1 µl and an accuracy of ± 8 µl. Lab 1 CMC  up to 1000 µl  ± 0.5 µl Reference Mass  Class E2 Lab 2 CMC  up to 5000 µl  ± 8.0 µl Reference Mass  Not mentioned  Lab 1 can be chosen for the calibration for the above mentioned pipette

Availability of Service Some of NABL accredited Calibration Providers SlNo Laboratory Name District 1 Electronics Regional Test Laboratory South Thiruvananthapuram 2 Meter Testing & Standards Laboratory 3 Alfatek Services 4 SCTIMST 5 Sophisticated Test and Instrumentation Centre Kochi 6 Fluid Control Research Institute Palakkad 7 Isotech Metrology Solutions

Regulatory Authority Requirements To meet the accreditation requirements of foreign agencies like COFRAC, in house and traceable calibration may be sufficient. NABL require accredited calibrations meeting it’s published specific criteria‘s. (e.g. Specific Criteria for Calibration Laboratories in Mechanical Discipline – NABL 122) CE marking / GLP Studies may require accredited calibrations with approved work procedures, study protocols, traceability etc.

Cost of Calibration Calibration cost can be optimized by choosing the right calibration agency having required scope and CMC. Better scope means better quality, means more costly.

Position in Traceability Chain Calibration of Mass Set in FCRI , NPL – Time constraint, Cost, Transportation etc

Selection Criteria in Nutshell Factors to consider while choosing a calibrating agency Check the accuracy required for unit under calibration (UUC) based on the tolerance desired. Check the NABL scope of the calibrating laboratory whether it meets the requirement both for parameter, range and CMC. The Error and uncertainty expressed should be in terms of % of reading in the calibration certificate and not in % of full scale (FSD). Preference should be given to accredited calibration Laboratories since these labs fulfill the requirements of an international standard (ISO 17025) are considered to competent than other labs.

Calibration Periodicity

Calibration Periodicity One of the most significant decision to be made regarding calibration is how often an instrument has to be calibrated. Currently there is only some guidelines providing the necessary directions with respect to the calibration periodicity.

Calibration Periodicity Some reference documents for fixing the calibration interval ILAC G-24: Guidelines for the Determination of Calibration NSCL RP1: Establishment and Adjustment of Calibration NIST GMP-11 – Assignment & Adjustment of Calibration Intervals for Laboratory

Calibration Periodicity Factors need to be taken into consideration while fixing calibration interval are Type of Instrument Frequency of Usage Manufacturer’s recommendation Maintenance and Service Accuracy of measurement sought Frequency of cross check Penalty of incorrect measurement data getting accepts

Calibration Periodicity using penalty factor New Calibration Interval = Current Interval * 50 / P Where P is the penalty factor estimated for the instrument. Reference :‘A practical approach for calibration interval’ (STQC)

Calibration Periodicity – Penalty Factors Sl No Factor Penalty Factor (Feature and Rating) 1 Accuracy Very Fine 10 Coarse 2 Frequency of Usage Very High Very low 3 Construction / Type Very delicate Robust 4 Required Skill level in operation 5 Operating Environment Shop Floor Clean Area 6 Maintenance Requirement Very frequent Infrequent 7 Nature of measurement technique New Established 8 Age of the equipment Very old Relatively new 9 Stability of calibration Very high Cost of Calibration Low TOTAL 100 20

Estimating Calibration Periodicity Sl No Factor Penalty Factor 1 Accuracy (± 1C) 2 Frequency of Usage (daily 2 times) 4 3 Construction / Type (Digital) 5 Required Skill level in operation (medium) Operating Environment (Heated) 6 Maintenance Requirement (very low) 7 Nature of measurement technique (Established) 8 Age of the equipment (3 years) 9 Stability of calibration (Good) 10 Cost of Calibration (Rs.2500/cal) TOTAL 40 For example, calibration periodicity of a digital thermometer can be estimated as, Calibration Interval, CI =( 1 * 50) / 40 = 1.25  CI can fixed as 1 Year

When to recalibrate ? In some cases equipments has to be recalibrated other than routine recalibration interval. If the exact performance of the equipment is not known If the equipment is under gone any repair. If there is any doubt in the performance of the equipment.

Interpretation of Calibration Reports

Calibration Reports Calibration Reports are the records that provides clients the results and outcomes of a calibration process. Calibration reports / certificates are used for the following activities. Applying correction to an instrument reading. Characterizing the accuracy of an instrument. Calculating the uncertainty in further measurement.

Applying correction Thermometer calibration results Corrected Temperature at 110 C is 110 + -0.3 = 109.7 C The spacing and number of points selected are sufficient to allow corrections for any reading to be deduced with sufficient accuracy by linear interpolation. As a general rule, extrapolation of corrections is not recommended.

Characterizing the accuracy We can describe the variations in terms of the centre and the width of the distribution of readings.

Calculating the uncertainty In estimating the uncertainty of a measurement, the equipment used as a reference has a role. In uncertainty calculation, the accuracy of the reference equipment and uncertainty of the reference equipment are major contributors of uncertainty. The above mentioned uncertainty is available from the calibration certificate of reference equipment used.

Contents of Calibration Reports When a Calibration Certificate for an equipment is received, it can be confusing to know what is important and how to interpret the information provided. The report should contain, The details about the UUC– Unit Under Calibration The calibrating laboratory’s reference equipment details The test method used The results including the corrections The uncertainty

Requirements of Calibration Reports The ISO 17025 standard defines what are the things to be includes in a Calibration report, in it’s clause “5.10.2”. The basic requirements are, The Title: The calibration certificates establish what the document claims to be. Name and address of calibration laboratory The user and laboratory can trace all work relating to the calibration and the use of an instrument. Each page should be numbered and the total number of pages given. Unambiguous identification of the instrument, including make, model and serial number.

Requirements of Calibration Reports Contd. Date of calibration Identification of calibration method used or unambiguous description of any non-standard method used, and/or deviation from standard method Conditions under which the calibration is carried out e.g. Environment like ambient temperature, pressure, etc Measurements and derived results A statement of the estimated uncertainty of calibration results A signature and title of person (s) accepting responsibility for the report contents A statement that the certificate shall not be reproduced other than in full, except with the approval of Top Administrator of the Calibration Laboratory.

Sample Calibration Report Details of Calibration Laboratory

Sample Calibration Report Details of Accreditation of Calibration Laboratory

Sample Calibration Report Unique Calibration Report ID

Sample Calibration Report Details of Requesting Person / Organization

Sample Calibration Report Details of Equipment Calibrated (Unit Under Calibrated)

Sample Calibration Report Details of Authorized Personnel of Calibration Laboratory

Sample Calibration Report Page number with number of pages in Calibration Report

Sample Calibration Report Contd… Date of Calibration

Sample Calibration Report Contd… Specification of Unit Under Calibration

Sample Calibration Report Contd… Details of Environment during Calibration procedure

Sample Calibration Report Contd… Details of Reference Equipments including calibration traceability

Sample Calibration Report Contd… Details of CMC (Calibration & Measurement Capability) of Calibration Laboratory if it is accredited

Sample Calibration Report Contd… Results of Calibration

Sample Calibration Report Contd… Procedures & Standard documents adopted for calibration.

Sample Calibration Report Contd… Details of Calibration Operators

Sample Calibration Report Contd… End of Calibration Report

Acceptance of Calibration Reports In order to receive “Technically valid Calibration / Test results competent to Global Metrology System, following actions can be taken. Verify the accredited scope of the laboratory on Accreditation body’s web site whether it meets the requirement both for parameter, range and CMC. Visit / enquire about the laboratory to verify its existence, available facilities, Competency and suitability to your requirement. To protect the genuine accredited laboratories and to prevent the malpractices those are defaming the country, please do not encourage or do not collude in such activities like getting reports without performing actual calibration, Using of logo of accreditation bodies without proper information etc. Providing review of report points

Updates

Updates NABL India (http://www.nabl-india.org/nabl/index.php?c=publicaccredationdoc&m=index&docType=both&Itemid=199) NPL India (http://www.nplindia.org/centre-calibration-testing-cfct) NPL UK (http://www.npl.co.uk/publications) Measurement Standards Laboratory, New zealand ; MSL (https://www.msl.irl.cri.nz/training-and-resources/technical-guides) National Association of Testing Authorities, Australia ; NATA (http://www.nata.com.au/nata/accreditation-publication/technical-documents-updates)