Currently in the U.S. there are two national standards for calibration laboratories such as, the ANSI/NCSL Z540-1 (Z540-1) and ISO/IEC 17025. Having two different national standards can be confusing for both laboratories and customers; therefore, we have put together a brief guide to describe the basic differences between the two standards.
UNDERSTANDING ANSI/NCSL Z540-1
Z540-1 differs from 17025 because it pertains only to calibration laboratories. Z540-1 particularly stresses both calibration and verification of measurement instruments and equipment. Under this national standard, calibrations are validated through internal quality control methods. What this means is that a system within a laboratory controls the calibration process. The system also controls the verification that each instrument or piece of equipment meets laboratory standards.
Z540-1 requires traceability of measurements to national standards, along with international standards or intrinsic standards. It is required for Z540-1 to include statements of traceability on all calibration reports.
Another contrast between the two standards is that Z540-1 requires labs to ensure calibration uncertainties are “sufficiently small.”
UNDERSTANDING ISO/IEC 17025
17025 differs from Z540-1 because it was written to include the requirements for both calibration and testing laboratories. 17025 focuses specifically on the competency of personnel providing the test and calibration services, along with the conditions/environment of the lab in which the services are being performed in.
Unlike Z540-1, 17025 requires traceability to SI units. In short, this means that traceability is established through the laboratory standards and consists of an unbroken chain of calibrations. 17025 states that traceability must be assured by the use of laboratory personnel and also requires proof of traceability. ISO/IEC 17025 also requires that measurements are traceable back to a national standard.
When it comes to measurement uncertainty, 17025 is more strict than Z540-1. 17025 requires a thorough and comprehensive uncertainty analysis for all calibrations performed. 17025 believes that traceability cannot be established without knowing the correct uncertainty ratio.