Accredited Calibration

Why is accredited calibration so important? 

There is always an unknown finite, non-zero difference between a measured value and the corresponding "true" value, which means no measurement is ever 100% completely correct. It is important to note that all labs and standards (including national ones) have measurement uncertainties that make impossible 100% confidence that an instrument operates within its stated tolerance limits or uncertainty bands. However, regular calibration by a laboratory accredited to national standards minimizes falling outside these limits and ensures the lowest acceptable measurement uncertainty for measurement points specific to that instrument to give users confidence that their test results are as accurate as is possible.
 

How does accredited calibration benefit end-users?

Proper and regular calibration from an accredited calibration laboratory means instruments are adjusted and maintained in accordance with original factory specifications and traceability of measurements and calibration are set to national standards. In addition, the calculation and documentation of the instrument's uncertainty values are provided, so that users can be confident in the accuracy of their instrument's calibration.
 

What is ISO/IEC 17025:2005?

The International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) first issued the standard in 1999. Recognized globally, it is the single most important standard for calibration laboratories. Labs accredited to this international standard demonstrate technical competence and produce test and calibration data that is precise and accurate.
 

What is the difference between Calibration and Adjustment?

Calibration compares a measuring instrument's performance against a national standard of known accuracy to gain quantifiable confidence in its measurement system. This determines if there is a need to then adjust the instrument and to what extent. Instruments are initially adjusted at the factory to indicate a value that is as close as possible to the currently-accepted known standard of accuracy. Measurement uncertainties of the known standard dictate the confidence that the value from the intial adjustment is "correct." Over time, this initial value may drift due to environmental factors (temperature, humidity, oxidation, loading, etc.), which are also dependent on the quality of its design and manufacture. Regular comparison of an instrument's performance to known standards ensures it continues to operate within the manufacturer's tolerances as the instrument can once again be adjusted to meet the standards.

Laboratory Decision Rule for ISO17025 Accredited Calibrations

The purpose of this statement is to provide advance notice of the decision rule used by Yokogawa’s calibration laboratory when providing calibration certificates. The laboratory uses a guard-band method which is described as follows:

• ILAC-G8:03/2009 The guard-band (G) is the specification (S) minus the expanded uncertainty (U) at a 95% confidence interval: G = S - U_95%

Measurement results are reported as follows:

• Passed (Pass) The measured values of the equipment were observed in specification at the points tested. Additionally, the expanded measurement uncertainty intervals about the measured values were in specification.
• Passed Indeterminant (Pass?) The measured values of the equipment were observed in specification at the points tested. However, a portion of the expanded measurement uncertainty intervals about one or more measured values exceeded specification. Consequently, compliance with specification cannot be declared based on the stated coverage probability.
• Failed Indeterminant (Fail?) One or more measured values of the equipment were observed out of specification at the points tested. However, a portion of the expanded measurement uncertainty intervals about one or more measured values were in specification. Consequently, non-compliance with specification cannot be declared based on the stated coverage probability.
• Failed (Fail) One or more measured values of the equipment were observed out of specification at the points tested. Additionally, the expanded measurement uncertainty intervals about one or more measured values were entirely outside the specification.

In the circumstance that the methodology described above is not acceptable, it must be communicated at the time of request to Yokogawa. Yokogawa’s calibration laboratory will strive to comply with reasonable decision rule requests, though it is possible that complexity or laboratory constraints will interfere with certain requests.