ISO 17025: 2017 Clause 6.4 Equipment (6.4.5 & 6.4.7)

The clause (6.4.5) states that:

The equipment used for measurement shall be capable of achieving the measurement accuracy and/or measurement uncertainty required to provide a valid result.

Capability: The equipment must be technically capable of achieving the required level of accuracy or uncertainty. This involves factors like its measurement range, resolution, and calibration capabilities.

Accuracy and Uncertainty: These are two different ways to express the reliability of a measurement. Accuracy refers to how close a measurement is to the true value, while uncertainty indicates the range of possible values within which the true value is likely to lie.

Valid Result: The ultimate goal is to ensure the equipment produces meaningful and reliable results. If the equipment's capabilities don't meet the required accuracy or uncertainty, the results could be misleading or inaccurate, jeopardizing the validity of the entire testing or calibration process.

Key considerations for laboratories:

Selecting equipment: Carefully consider the required accuracy or uncertainty before purchasing or using any equipment. Consult technical specifications, manufacturer recommendations, and relevant standards.

Calibration and maintenance: Regularly calibrate equipment to ensure it maintains its accuracy over time. Follow proper maintenance procedures as recommended by the manufacturer.

Documentation: Maintain records of all equipment, including calibration certificates, maintenance logs, and performance checks. This demonstrates compliance with ISO 17025 and helps identify potential issues early on.

 

Clause 6.4.6 emphasizes that measuring equipment should be calibrated under specific conditions, such as when the accuracy or uncertainty of the equipment could impact the validity of reported results or when establishing metrological traceability is required. It recognizes the importance of ensuring the accuracy of equipment involved in direct measurements, corrections, and calculations to maintain the reliability of laboratory results.

 Types of Equipment for which calibration is required:

   -  Direct Measurement Equipment:  Equipment used for the direct measurement of the measurand (the quantity being measured), such as a balance used for mass measurement.

   -  Correction Equipment:  Equipment used to make corrections to the measured value, for example, equipment used for temperature measurements where corrections may be necessary.

   -  Calculation Equipment:  Equipment used to obtain a measurement result calculated from multiple quantities. Calibration is necessary to ensure the accuracy of calculations based on multiple inputs.

Impact on Result Validity

Calibration is necessary when the measurement accuracy or uncertainty directly affects the validity of the reported results. This means:

Inaccurate measurements: If the equipment deviates from the true value by an amount that could significantly impact the interpretation of the test results, it needs calibration. For example, an inaccurate balance in measuring food samples could lead to incorrect assessments of nutrient content or contamination levels.

Excessive uncertainty: Even if the average measurement is close to the true value, a high level of uncertainty indicates a wider range of possible values. This can make it difficult to draw definitive conclusions from the test results. For example, high uncertainty in measuring pesticide residues might raise concerns even if the average level falls below safety limits.

Metrological Traceability

Calibration is required when it's crucial to establish the metrological traceability of the reported results. This means ensuring a clear and unbroken chain of comparisons back to international standards:

Linking measurements to international units: All measurements should ultimately be traceable to internationally recognized units like meters, kilograms, or degrees Celsius. Calibration ensures that the equipment's measurements align with these standards.

Demonstrating measurement integrity: Traceability provides documentation and evidence that the equipment is functioning correctly and producing reliable results, essential for maintaining laboratory accreditation and demonstrating compliance with regulations.

Examples of Equipment Requiring Calibration:

Direct measurement: Balances for weighing samples, thermometers for measuring temperature, pH meters for acidity levels.

Corrections: Thermometers used to correct for ambient temperature during food analysis, barometers for pressure corrections in specific tests.

Calculated results: Spectrometers for analyzing chemical composition, where final results depend on accurate measurements of multiple parameters.

 

 Clause 6.4.7 emphasize that  the laboratory needs to create a plan (calibration program) to regularly check and adjust its measuring equipment. The plan should be flexible and updated as needed to make sure the equipment is working correctly.

A laboratory that tests the concentration of chemicals in water samples. Their measurements rely on various instruments like pipettes, balances, and pH meters. According to the clause:

Establish a Calibration Programme: They need a documented programme outlining which instruments require calibration, how often they need it (based on manufacturer recommendations, usage frequency, or risk assessment), and who is responsible for performing the calibrations.

Review and Adjust: This programme shouldn't be static. The laboratory should regularly review its effectiveness (e.g., annually) and make adjustments as needed. For example, if a specific instrument shows unusual drift or instability, they might tighten its calibration frequency.

Maintain Confidence: The ultimate goal is confidence in the calibration status of every instrument. This means having documented records of calibrations, including dates, calibration data, and any adjustments made. It also involves ensuring calibration is performed by competent personnel using accredited calibration providers or traceable reference materials.

Benefits of a Robust Calibration Programme:

Accurate and reliable results: Ensures measurements and test data are trustworthy, minimizing errors and increasing customer confidence.

Compliance with regulations: Many industries and regulations require laboratories to have documented calibration programmes.

Reduced risk: Detects and corrects potential issues with equipment before they impact results, minimizing errors and liability.

Improved efficiency: Optimized calibration schedules prevent unnecessary calibrations and ensure instruments are always in good working order.

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