CCT Calibration Standards & Regulations 5 — Questions and Answers
Question 1: What is the key difference between 'verification' and 'calibration' in metrological practice?
- Verification uses more accurate equipment than calibration
- Calibration determines deviation from a standard; verification confirms conformance to a specification (Correct answer)
- Verification is performed by accredited labs only; calibration can be done by anyone
- Calibration is required by law; verification is optional
Correct answer: Calibration determines deviation from a standard; verification confirms conformance to a specification
Calibration determines the relationship between instrument output and true value (with uncertainty), while verification confirms whether the equipment meets specified requirements — it typically results in a pass/fail decision.
Question 2: What is a 'calibration interval' and what factors influence its determination?
- The time between laboratory audits, set by the accreditation body
- The period between successive calibrations, influenced by stability history, usage, and risk (Correct answer)
- The time allowed for a technician to complete a calibration
- The gap between instrument readings during a single calibration session
Correct answer: The period between successive calibrations, influenced by stability history, usage, and risk
A calibration interval is the period between successive calibrations of an instrument, determined by factors including measurement stability history, frequency and severity of use, environmental conditions, and risk of out-of-tolerance condition.
Question 3: Which standard provides guidance on the selection and use of statistical methods for calibration interval analysis?
- ISO/IEC 17025
- NCSL RP-1 (Correct answer)
- ISO 10012
- ANSI/NCSL Z540.1
Correct answer: NCSL RP-1
NCSL Recommended Practice RP-1 provides methods for optimizing calibration intervals based on historical in-tolerance data and defined reliability targets.
Question 4: What action is required when a reference standard is found to be out of tolerance upon return from external calibration?
- Immediately destroy the standard and order a replacement
- Assess the impact on all measurements made since the last valid calibration and take corrective action (Correct answer)
- Recalibrate all customer equipment at no charge
- File a complaint with the accreditation body
Correct answer: Assess the impact on all measurements made since the last valid calibration and take corrective action
Finding an out-of-tolerance reference standard triggers a retrospective impact assessment to determine whether previously issued calibration results may have been affected, followed by appropriate corrective actions.
Question 5: Which concept describes the degree to which a measuring instrument gives the same reading when measuring the same quantity under the same conditions?
- Accuracy
- Repeatability (Correct answer)
- Resolution
- Linearity
Correct answer: Repeatability
Repeatability is the closeness of agreement between repeated measurements of the same measurand under identical conditions — it is a component of precision, not accuracy.
Question 6: Under ISO/IEC 17025:2017, what must a calibration certificate include regarding measurement uncertainty?
- Uncertainty is optional and only included on customer request
- The measurement uncertainty must be reported whenever it is relevant to the validity or application of the results (Correct answer)
- Only the expanded uncertainty at k=3 must be stated
- Uncertainty must be expressed as a percentage of the nominal value only
Correct answer: The measurement uncertainty must be reported whenever it is relevant to the validity or application of the results
ISO/IEC 17025:2017 requires that calibration certificates include measurement uncertainty when it is relevant to the validity or application of the calibration result.
Question 7: What does 'documentary evidence of traceability' on a calibration certificate typically include?
- The serial number of the instrument only
- Reference to the higher-level calibration certificate, standard used, its uncertainty, and accreditation status (Correct answer)
- A photograph of the calibration setup
- The technician's professional certification number
Correct answer: Reference to the higher-level calibration certificate, standard used, its uncertainty, and accreditation status
Documentary evidence of traceability includes identification of the reference standard used, its calibration certificate number, the uncertainty of that standard, and the accreditation body endorsing it.
CCT Calibration Standards & Regulations 5
What is the key difference between 'verification' and 'calibration' in metrological practice?