Calibration Process and Equipment Requirements...

Information & Training. | Quality Assurance. Quality Management.

The importance of Calibration. A well managed calibration system is essential in all manufacturing and monitoring operations. It provides confidence in the measured data and consistency in the measuring, test, manufacturing process. It is a requirement of ISO 9000, plus other regulatory standards and is often a customer requirement.


What is Calibration?

• Calibration is checking the lack of certainty (uncertainty in measurement) of a measuring instrument.
• Is achieved by checking something that has a know value (traceable standard) and noting the output of our measuring instrument.
• The difference between both is the error.


Calibration requirements include the need to…

• Establish and maintain documented procedures.
• Determine measurements to be made and accuracy required.
• Select an appropriate measurement instrument capable of measurement accuracy and precision.
• Identify and define measurement instrument for calibration.
• Calibrate to prescribed intervals and to national and international standards. (ILAB, NAMAS, NIST).
• Where no standards exist, document the basis used for calibration. (e.g. Test Fixtures, Autocollimators, etc.)
• Define the calibration process and specify the acceptance criteria.
• Label measurement instruments with a suitable indicator to show calibration status.
• Publish calibration status reports on defined intervals.
• When measurement instruments are not conforming, take appropriate action on same and product affected.
• Maintain calibration records.
• Protect measurement instruments from damage, misuse and deterioration. (Use suitable packaging when not in use)
• Safeguard measurement instruments, including software and hardware, from adjustments which would invalidate the calibration setting.

Calibration terms and definitions:

• Measurement Instrument – Any instrument which monitors or controls a critical parameter of a manufacturing process, controlled environment or used to measure a product or component specification.
• Standard – A defined reference tool with traceability to a national standard.
• National standard – A reference tool utilized by an internationally recognized standards laboratory representing the country which operates that laboratory.
• Calibration – Verification of a measurement instrument’s performance against a traceable standard.
• Precision – Or repeatability. Variation in readings obtained when repeating the exact same measurement(s).
• Traceability – Documented reference of calibration results to a recognized standard.
• Accuracy – The relative agreement of a measured value with an accepted standard.
• Loop Calibration – The calibration of measurement instruments “as installed” in a total system and represents calibration of the instruments “as used”.
• Resolution – The power of discrimination of an instrument.
• Range – The breadth or span of an instruments capability of measurement.


Typical calibration user responsibilities in an organization…

• Equipment user shall forward equipment to the calibration coordinator if (say) new batteries are required.
• Equipment user shall forward equipment to the calibration coordinator if there is a damaged or non-functional or missing or unreadable calibration label.
• Equipment user shall check equipment calibration due date prior to use to ensure it has not expired.
• Non-portable equipment, equipment user shall inform calibration coordinator if there is a damaged or non-functional or missing or an unreadable calibration label.
• Equipment user shall ensure proper use, handling and storage for assigned test equipment.


Typical calibration representative responsibilities in an organization…

• Department calibration representatives shall attend regular calibration status meetings.
• Department calibration representatives shall perform monthly calibration equipment stock check with status reports provided by calibration coordinator.
• Department calibration representatives shall complete & return status reports to the calibration coordinator.
• Department calibration representative shall coordinate search for missing equipment within their respective department.


Identification requirements for calibration…

• Identify and list all measuring instruments including personal measuring devices.
• Include all equipment involved with quality control measurements, including test fixtures and software based measuring applications.
• Clearly identify all equipment not to be calibrated with a suitable indicator.
• Quarantine measuring instruments that are not calibrated. If unable to remove, label the item “Do Not Use” and make inoperable if possible.


Selection of suitable equipment…

• Criteria for selection of measuring instruments include appropriate accuracy, precision and resolution.
• Test uncertainty ratio of 4:1 or better must apply to accuracy. Documented rational required if (say) a test uncertainty ration of 4:1 cannot be achieved.
• Ease of use – portable, reliable, industry standard.
• Digital display preferred as analogue tends to lend itself to more interpretation during reading results.


Calibration database…

• Must list all calibrated measuring instruments and standards.
• Update immediately as new equipment is purchased.
• Indexed by instrument serial number.


Equipment coding system and control…

• Measuring instruments are tracked by original serial number.
• Calibration records must identify this unique serial number.
• Code number must be unique and not re-used when instrument is discontinued.
• Should be permanently marked, etched on the equipment.
• Battery replacement must be performed by the calibration department.
• Security seals, anti-tamper labels should be replaced by the calibration department.
• Software used for testing is validated, controlled and protected.
• Manufacture’s user manual, specification and calibration records archived in central area.


Setting calibration intervals…

• A calibration interval is the maximum period between successive calibrations.
• Not possible to construct a list of intervals which can be universally applied.
• Based on manufacturers recommendation, extent and severity of use.
• Documented engineering rationale based on usage.
• If none of the above available, interval not greater than 6 months would be a good starting point.
• Apply trend data obtained from previous calibrations.
• Need to consider any tendency to wear and drift with equipment ageing.
• Need to consider the risk and potential impact of an incorrect measured value being accepted.


External calibration…

• Performed by quality assured and approved subcontractors with accreditation for the relevant measuring instrument.
• Calibration to be performed to the manufacturers specification across the full instrument range.
• Calibration coordinator should approve calibration certificates.
• Have traceability to a national standard, e.g. NIST, ILAB, NMAS.


Internal calibration…

• Calibration personnel must use application specific procedure.
• Fully trained personnel only.
• Environmental conditions must be considered and established.
• Provide instruction on calibration points, required accuracy and precision.


Calibration records & certificates…

• Include measurement instrument ID.
• Calibration date and due date.
• Signature of person performing the calibration.
• Identity of standards used and due date.
• Identity of procedure and revision ID.
• Before and after data (if adjusted) for each calibration point.
• Statement of acceptability (pass or fail).
• Tolerances for accuracy and precision.



• Measuring instrument owner is responsible for submitting new equipment, equipment due and non-conforming equipment to calibration department.
• All measuring instruments require ID and status label.
• Traceability required for internal and external calibration.

Information & Training. | Quality Assurance. Quality Management.

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