I recently returned from Tokyo where Audio Precision has been working to set up a new calibration facility for our many good customers in Japan. Our customers depend upon the accuracy of Audio Precision products for their testing needs. Similarly, Audio Precision must be able to ensure the performance of our analyzers and products using even higher accuracy laboratory test equipment. To accomplish this task, we have developed an automated test station running our own proprietary software. A number of these stations have been established at various locations around the world in addition to the two we maintain at our factory in Beaverton, Oregon.
Calibration is an extremely fascinating topic that immediately takes one into the realm of metrology, or the science of measurement. Unfortunately many engineers seem to have only a very superficial, and sometimes very incorrect, understanding of what the word “calibration” actually means.
First, calibration is a process of comparison and documenting results. “Calibration” should not be confused with the word “adjustment”, although the two words were once used almost interchangeably as recently as the 1970s. The end result of calibration is a certificate and report containing the actual observed results of the device or product being tested.
Second, calibration should assert “traceability” to a national standard. Traceability is nothing more than an unbroken chain of comparisons to the highest level of standards maintained by a country. In the United States this is typically NIST. Other countries may maintain their own standards. These standards are occasionally compared to each other in a process called an inter-laboratory comparison, or ILC, to insure international agreement.
Third, and perhaps most important, calibrations should be accredited. At Audio Precision we maintain accreditation to ISO/IEC-17025, the highest possible level of accreditation. We are periodically audited by a recognized accrediting agency that reviews our quality control system, quality manual, records of how we reacted to customer issues or complaints, and the supporting calculations of measurement uncertainty that must accompany every numerical measurement. Only the very best and quality conscious manufacturers of test and measurement equipment offer accredited calibrations.