Jack E. West  |  10/03/2008

Measuring the Measurement Equipment

Controlling the calibration and use of measuring devices is key to product conformity.

Perhaps no concepts have been more abused than those related to controlling measurements. For decades it was common in many industries to calibrate measuring and test equipment to ensure it met its own specifications for accuracy and precision. Complex and expensive systems were developed to do the calibrations as scheduled. There was little emphasis on controlling the relationship between the requirements being measured and the precision, accuracy, and stability of the overall measurement system. I’ve seen many situations where measuring devices had tolerances that were looser than the tolerances of the characteristic being measured, and caused the entire control loops to behave erratically--and the managers all wondered why.

By the time ISO 9001 was first issued in 1987, this had begun to change. Some industries had begun to emphasize what should be measured so that appropriate measurement equipment was selected. Still, even today it’s not uncommon to see the wrong equipment being used for a measurement. The most important focus in this area is to establish controls to ensure that measurement capability exists. In other words, the measurement system must be accurate and precise enough to ensure that measurements meet measurement requirements.

Measurements must be made to ensure that products meet specifications. The necessary measurements should be identified, along with any special instruments or monitoring and measurement devices needed for making them. ISO 9001, subclause 7.6 requires an organization to establish processes to ensure that monitoring and measurement can be carried out and are carried out in a manner consistent with the monitoring and measurement requirements. This equipment selection is, perhaps, the most important part of subclause 7.6. This part of the standard focuses on ensuring the quality of the measurements as well as the monitoring and measurement devices. If the devices used to make measurements aren’t accurate, are unstable or damaged in any way, or are inappropriate for making the measurement, then the product might not meet its requirements. Even worse, the organization won’t know this. Monitoring and measurement devices must be capable, and their use must be controlled.

All monitoring and measurement instruments or equipment required to ensure that a product conforms to requirements fall within the scope of this subclause. It’s useful to understand the difference between “monitoring” and “measuring.”

Monitoring implies observing, supervising, keeping under review (i.e., using monitoring devices). It can involve measuring or testing at intervals, especially for the purpose of regulation or control.

Measuring determines the physical quantity, magnitude, or dimension of something (using measuring equipment).

Although subclause 3.10.4 of ISO 9001 defines measuring equipment as “measuring instrument, software, measurement standard, reference material or auxiliary apparatus, or combination thereof necessary to realize a measurement process,” the standard only requires “measuring equipment” to be calibrated when it’s used “… to provide evidence of conformity of product to determined requirements,” either by product or process measurements.

Monitoring and measurement devices that are required to ensure product conformity must be controlled. This includes devices used during design and development, for inspecting and testing raw materials, for in-process and final testing, and for monitoring quality once a product has been released to the customer.

The extent of the control to be exercised over monitoring and measurement devices is listed in items A through E of subclause 7.6. Although the concept of a measurement system isn’t specifically addressed in the standard, subclause 7.6 provides the framework for establishing and maintaining a measurement system. When measuring equipment doesn’t conform to requirements, any measurements made since the equipment was last known to be in conformity must be investigated and validated. Records of calibrations and verification measurements must be kept.

Monitoring and measurement are key activities in an organization’s processes to ensure conformity. Proper control and use of monitoring and measuring equipment is critical. Without proper controls and equipment use, it’s likely that much of the monitoring and measurement effort is just a waste of time.

For further information on this subject, see Chapter 8 of ISO 9001:2000 Explained, Second Edition, by Charles A. Cianfrani, Joseph J. Tsiakals, and me (ASQ Quality Press, 2001).


About The Author

Jack E. West’s picture

Jack E. West

From 1997 through 2005 John E. (Jack) West was chair of the U.S. TAG to ISO/TC 176 and lead delegate for the United States to the International Organization for Standardization committee responsible for the ISO 9000 series of quality management standards. He remains active in TC 176.