Calibration – the Sure Way to Accurate Measurements
01 Mar 2006
In addition to fulfilling industry requirements, calibration is about always being sure that your equipment produces valid results with known uncertainty.
During testing, microphones and accelerometers can change sensitivity or break. They might look intact, but what happens if you continue measuring without having calibrated your transducer? Can you trust your data? Do you have to redo the entire test? In cases of extreme testing you might only have one shot at getting your measurement right as the product gets destroyed during the testing process. So by calibrating your instrument you can minimise or even eliminate the risk of invalid data, and avoid the cost of repeating the process.
Aircraft manufacturers have to comply with very strict calibration requirements for Flight and Static Acoustic Certification testing. These are defined by the International Civil Aviation Organization (ICAO) and include, for example, requirements such as:
- A valid accredited calibration for all microphones and calibrators prior to testing
- A frequency response calibration of the entire measurement chain
- Complete amplitude calibration before and after each flight or static test to ensure that the system is within acceptance limits
For example, every time GE Aviation performs static acoustic certification testing to support aircraft manufacturers, they are required by ICAO and the U.S. Federal Aviation Administration (FAA) to calibrate microphones within 90 days of a test, and to calibrate pistonphones and Brüel & Kjær’s signal generator within 6 months. They follow these requirements rigorously, although there has been no degradation in the frequency response of the microphones – in fact, the microphones have not varied significantly over 10 years and at least 8 Brüel & Kjær calibrations. The same applies to the calibrations performed on GE’s pistonphones over the past 20 years.
But although Brüel & Kjær equipment and calibration is renowned for its stability, this is not enough to satisfy the demands made on industries such as the aerospace and automotive industries.
When Brüel & Kjær calibrates your transducers, the microphone or accelerometer is compared with a reference standard. It is of utmost importance that you can trust these references – stability and traceability ensure that your data is valid. The Brüel & Kjær operated Danish Primary Laboratory of Acoustics (DPLA) has reference transducers with unsurpassed long term stability, with data available for more than 35 years.
All Brüel & Kjær calibration is documented, traceable and performed in accordance with the relevant standards. Our calibration laboratories are accredited in many regions, fulfilling the requirements of DANAK, A2LA, COFRAC, E.N.A.C., and NATA. International traceability and verification is obtained by performing key comparisons of reference transducers between the National Metrology Institutes, for instance PTB and NIST.
We offer primary calibrations for transducers through DPLA. We perform hundreds of primary calibrations annually, on reference microphones and accelerometers, some for national metrology institutes, which maintain national reference standards for the industry.
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