Calibration and ISO 9001:2000

A manufacturer’s calibration program is the basis of its quality controlling activities. A good calibration program can do more than reduce scrap rates. It can reduce expenditures for measurement instruments and related services, add to the confidence and expertise of the company’s staff, and increase the customer’s perception of company performance. A good calibration program can protect the company from big risk, and provide records of internationally standardized metrology that would be hard to dispute.

It can be said that a manufacturer’s calibration program is built upon three foundations. First, an understanding of the technical details of the tools in use must be maintained and utilized. Second, the measurement unit in use must be traceable to the internationally agreed upon standard. Third, the calibration program must be managed.

Valid calibration procedures

Measurement instruments and tools differ greatly in construction and intent, and the specific activities necessary to calibrate these tools are just as varied. An understanding of the operation of each tool allows problems to be detected, adjustments to be made properly, and condition of tools to be assessed. These technical details are found in calibration procedures.

The calibration procedure, to be effective, has to be valid to the tool that will be calibrated. It is very important for a manufacturer to design its calibrations around the specific tools and how they will be used.

There are many sources of historically validated calibration procedures for dimensional metrology tools.

Many valid calibration procedures are available through activities of the United States Government. Standards that are published by different branches of the military may be available to civilian contractors, if they do business with government. Freely distributed standards published by the government and military are readily available online. Trade organizations publish standards that can be purchased.

The manufacturers of dimensional metrology tools can also be a great source of valid, proven calibration procedures. Calibration laboratories used for calibration of more complicated or demanding tools and reference specimens may be willing to share their procedures.

Staff experience can also be an excellent source of data on calibration.

Traceability

The definition of traceability that has achieved global acceptance in the metrology community is contained in the International Vocabulary of Basic and General Terms in Metrology (VIM; 1993):

"…the property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons, all having stated uncertainties."

Traceability of a measurement unit is really maintained by a dual chain of metrology that goes back to the international standard. Each comparison is accompanied by an estimation of measurement uncertainty. Measurement uncertainty is calculated through an internationally standardized discipline.

While some might consider measurement uncertainty calculations complex or time consuming, the actual process is really not that difficult. “Experience shows that with just a little bit of practice most people who have a basic knowledge of metrology can successfully identify the three to five largest uncertainty contributors. That is all it takes to make an uncertainty budget that is within 20% of the correct value, which is close enough to make it a valuable tool.” (Palumbo, 2006)

Measurement uncertainty calculations are not explicitly required by ISO 9001:2000. This revision’s less proscriptive and more widely applicable foundation leaves it up to the manufacturer to decide what the requirements of the individual measurement processes are. The requirements are then based on real world considerations of law, regulations, safety, customer requirements, applicable standards, and performance of the manufacturer’s measurement process itself.

The requirements for calibration of measurement tools can be found in section 7.6 of ISO 9001:2000. For insight into this section, it is useful to refer to the manufacturing centered 1994 version of ISO 9000. Section 4.11, Control of Inspection, Measuring, and Test Equipment states that measuring equipment is used in a manner that ensures that the measurement uncertainty is known and is consistent with the required measurement capability. The intent of the requirements in both versions is the same. In-house calibrations that are not accompanied by measurement uncertainty estimates have broken the chain of traceability.

Management

An ISO 9001:2000 management system strives to attain customer satisfaction through continual improvement of processes. In manufacturing, calibration and measurement is one of the most important processes we can define.

The management of the calibration process is accomplished in the same way as management of the other processes identified in the manufacturer’s management system. A cycle of planning, action, measurement and management will complete the solid basis of instrument calibrations, both those performed in-house and those outsourced to calibration laboratories.

Some manufacturers may choose to develop a calibration system manual which contains the process description, planned quality objectives, key indicators of process performance and references to the standards and procedures in use. This can become a very valuable document that serves as the roadmap to a dynamic, effective, top notch calibration program.

Good metrology delivers information about the manufacturer’s products. Using this information in an ISO 9000 based management system creates knowledge about the manufacturer’s products, machines and processes, capabilities, and tools.

A good calibration program will provide some immediate economic benefits and deliver protection from problems, but calibration is not a core business for most manufacturers. Internal calibration is not a product, and the immediate economic benefits of good metrology will be very limited or not even seen. However, a good calibration program will develop confidence on the factory floor that the company is dedicated to providing quality product. It will develop capability and expertise. It will develop pride in company staff, knowing fully well that their system is one of the best, and is only getting better. Good calibration is good metrology, which is a core aptitude of manufacturing organizations. It can only bolster and empower the organization as a whole.

1.  International Vocabulary of Basic and General Terms in Metrology (VIM), BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML (1993).

2.  Palumbo, Robert. “Gage Calibration Is an Investment in Quality Production.” Quality Digest Feb. – Mar. 1997