Understanding Calibration Standards

Calibration involves comparing the measurements a tool makes with those of a reference device traceable to national standards. Calibration standards define requirements for how calibrations should be performed, documented, and controlled, including how measurement uncertainty is evaluated and what traceability is required.

Industries from aerospace and defense to automotive and medical device manufacturing take slightly different approaches to calibration and have developed their own standards. While broadly similar, these have nuances that emphasize particular points important to their sectors. Some focus on how the calibration activity is organized, while others look at calculation and reporting of uncertainty.

When searching for a business to calibrate your assembly tools, it’s important to verify their understanding of the specific standards relevant to your industry. This blog examines some common standards and discusses the requirements for uncertainty and traceability.

ISO 17025

ISO/IEC 17025 is widely considered the gold standard for calibration laboratories. Most industry-specific standards are based on ISO 17025. This standard defines how a calibration function should be organized within a business. It addresses the lab processes used to achieve reliable calibration, along with personnel training, measurement traceability and uncertainty, and creation of calibration certificates.

When searching for a calibration service, compliance with ISO 17025 is the most important factor to consider. As ISO 17025 requires external audits, it provides a high level of confidence in the results produced.

ISO 9001

ISO 9001 refers to the Quality Management System standard used by many industries. It requires a calibration system in place that ensures the measurement equipment used to control product quality provides correct results. This system should include maintaining calibration records and determining appropriate calibration frequencies.

Unlike ISO 17025, ISO 9001 does not explicitly address how calibration functions and processes should be run. However, the clause on training indicates that those responsible for following calibration procedures should receive appropriate training. It also notes that any measuring equipment that becomes damaged or where accuracy is otherwise suspect should be withdrawn from use.

AS 9100

This is the aerospace industry version of ISO 9001, developed by the International Aerospace Quality Group (IAQG). As might be expected, AS 9100 builds on ISO 9001 by requiring tighter control over activities, including calibration, that can affect product quality.

Businesses compliant with AS 9100 are expected to apply frequent calibration intervals to quickly identify devices that provide unreliable measurements. They should also have procedures for handling any product that may have been assembled and/or inspected using measurement devices found to be out of calibration.

However, like ISO 9001, AS 9100 does not specifically address procedures for operating a calibration function. Again, that is covered by the more general clauses. Thus, an AS 9100-certified aerospace business should still plan on working with an ISO 17025-compliant calibration service provider.

IATF 16949

Similar to AS 9100, IATF 16949 is an automotive industry-specific quality management standard built on ISO 9001 and shares the same general requirements for calibration activities. IATF 16949 adds the requirement that all measurement systems be calibrated, not just those that directly affect product quality. The standard also requires more detailed calibration records, including evidence of conformity to specification after calibration.

ISO 13485

This ISO standard details quality management procedures for businesses that manufacture and service medical devices. As with other standards, it’s based on ISO 9001 and has several specific calibration requirements.

The biggest of these is requiring organizations to identify the measurement equipment required during the product development process. This equipment must have a required level of precision to ensure acceptable product quality.

Other sections cover the use of digital signatures in formal documents, such as calibration records, and the validation of the software used in measurement devices.

ANSI Z540.3

This standard grew out of MIL-STD-45662, which is still referenced in some documents despite being discontinued in 1995. It provides detailed requirements for calibration labs to follow, addressing traceability, uncertainty, and risk.

An important feature of ANSI Z540.3 is its requirement to quantify uncertainty. In particular, there is an expectation that calibration ensures a false accept risk of less than 2%. In other words, only one chance in 50 of a device being out of calibration when it is reported as being within the limits.

This makes the Z540.3 standard far more specific in terms of results achieved than the other calibration-related standards.

ISO 15189

This standard addresses quality management within medical laboratories. It builds upon ISO 9001 but also includes aspects of the ISO 17025 calibration standard. The rationale for this is that test results must be generated on equipment that yields dependable data with minimal levels of uncertainty.

Accordingly, equipment must first be selected for suitability, and then calibrated, maintained, and monitored to ensure traceability. Records must be maintained and will be subjected to audits. Calibration procedures must be in place, as required by ISO 9001.

Calculating Uncertainties in Calibration

Uncertainty exists in every measurement, and quantifying it is a core part of calibration. The ISO Guide to Expression of Uncertainty (GUM) was created to prevent calibration labs from expressing uncertainty in ways that could be misunderstood.

The GUM uses the concept of an uncertainty budget, in which the various sources of uncertainty are combined into a single figure. This incorporates the concepts of Type A (statistical) and Type B (non-statistical) uncertainties, both of which lead to uncertainty in the measured value.

Calibration labs that follow the GUM are committed to providing transparency and consistency to their calibration practices.

Ensure Better Traceability & Accuracy With ISO 17025-Compliant Calibration Services

Regular calibration ensures assembly tools provide the fastener-tightening precision needed across many industries. If you don’t have an in-house calibration lab, it’s critical to partner with an external lab accredited to ISO 17025.

Encore Systems is proud to have a U.S.-based lab accredited by ANAB to ISO/IEC 17025. All calibrations we perform are to the requirements outlined in ISO 17025. We also offer a tool management program to provide timely reminders when calibration is due.