special focus: calibration
Why, when and how often to check your instruments Regular calibration of equipment will validate data quality and documentation, minimise the risk of errors and reduce associated costs, says leading international company Brüel & Kjær provides services like sound level meter repair (pictured) and calibration is an important part of its offer to its customers
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s a world-leader in sound and vibration measurement and analysis, Brüel & Kjær recommends companies calibrate equipment on a regular basis to validate data quality and documentation, minimise the risk of errors and reduce associated costs. Brüel & Kjær – a subsidiary of UK-based Spectris plc – offers a comprehensive range of calibration services, to meet national and international requirements, for sound level meters, noise dose meters, calibrators and pistonphones, analyzers, microphones and preamplifiers, accelerometers and reference instruments. The company advises on calibration to help to create sustainable value for its customers. Below is some general advice.
Why calibrate? Regular calibration provides: • Knowledge and evidence of how your instrument measures – now and over time • Confidence that you know your instrument works correctly. According to the International Laboratory Accreditation Cooperation, the purpose of calibration is: • To know the uncertainty that can 30 | www.mepca.com
be achieved with the measuring instrument • To confirm whether or not there has been any alteration of the measuring instrument that could create doubt about the results • To improve the estimation of the deviation between a reference value and the value obtained using a measurement instrument, as well as the uncertainty in this deviation, at the time the instrument is actually used.
When to start calibration Brüel & Kjær recommends calibrating your instrument prior to use. The easiest way is to order initial calibration with every new instrument. In this way you begin a measurement history from day one, which can be required by your customers or quality procedures.
How often? How often you calibrate your instrument is a balance between risk and cost. The shorter the period between calibrations, the lower the risk of questionable measurements. We consequently recommend annual calibration for electrical instruments. Equipment used on a daily basis
will have a shorter calibration cycle than equipment used, for example, once a month. However, you should take into consideration: • Cost – the cost of necessary correction measures if you discover that the instrument has not been reliable over a long period of time • Instrument – the required uncertainty in measurements; extent and severity of use; trend data obtained from previous calibration records and tendency to wear and drift • Environmental conditions, transportation and personnel – climatic conditions, vibration, ionizing radiation, etc; transportation arrangement; degree to which personnel are trained. Brüel & Kjær has recently created a range of robust CCLD accelerometers for vibration measurements in harsh industrial environments. The new type 4533-B and type 4534-B accelerometers feature a high signal output-to-weight ratio and very low sensitivity to environmental influences, thanks to Brüel & Kjær’s patented ThetaShear® accelerometer design. This makes them ideal for general vibration measurements for a range of different applications, such as automotive parts, aircraft and industrial machinery. Bruel & Kjaer UK’s autumn training schedule is now open for registration. The company also offers free webinars, which run throughout the year. The company’s UK HQ is in Royston, Hertfordshire. Ring 01223 389800 for more details or visit the company website using the URL given below. bksv.co.uk