Power calibration lab meets ISO17025 up to 100kHz

There is a growing demand for more certainty in power measurements, particularly as the renewable energy market grows and the need to optimise efficiency is further realised. In addition, solar inverters are switching at higher and higher frequencies; a scenario which introduces higher-frequency harmonics. Higher frequency power measurements are also increasingly required for devices such as SMPS, electronic lighting ballasts, soft starters in motor controls and frequency converters in traction applications. As a result, Yokogawa has identified a need to offer accredited calibration, not just between 50 and 60Hz, but across a wide range of frequencies from 10Hz up to 100kHz.

Yokogawa has highlighted the recent ISO17025 accreditation as a key part of its long-term business strategy to maintain and grow its position at the forefront of the European digital power analyser market. “The recognition offered by ISO17025 accreditation is objective proof that the knowledge of our personnel and the quality of our instruments are at a world-class level,” commented Terry Marrinan, Vice President EMEA, Test & Measurement, Yokogawa. “For customers working with tight tolerances, ISO17025-accredited calibration of the measurement is vital to major critical measuring projects and provides the high level of quality assurance that our customers need.”

With today's stringent design requirements, engineers must be sure that the power measurements they make are correct. Their power meters need to be calibrated at the frequencies present in their specific applications, not just at 50Hz. A calibration result at 50Hz, no matter how good, gives no insight into higher-frequency performance. Yokogawa is also addressing modern challenges, listing parameters such as phase shift, power factor and distorted waveform effects alongside voltage, current and frequency. Yokogawa's extended capability allows it to calibrate currents up to 1200A_RMS at 50/60Hz.

Yokogawa's European Standards laboratory at work

I was invited by Yokogawa to travel to Amersfoort and tour the facility at the time of its announcement in October 2015. Surrounded by a plethora of much-loved, well-known instruments, lab manager and metrology specialist Erik Kroon acts as guardian and caretaker for the facility. With a background in ISO auditing, there are few engineers in the world who understand power measurement to the same extent and depth as Erik, who personally built several of the systems operating in the Amersfoort lab. The laboratory is kept at a stable 23°C, at constant humidity, and is airlocked and EMI-proofed, with only a select few engineers granted access.

Part of Erik Kroon and Yokogawa's claim to incredible accuracy and repeatability lies in the hardware which fills its European standards laboratory. With some instruments having seen up to 40 years of service, every device used has been continuously calibrated for at least 5 years to ascertain its stability. Traceability is ensured as a long-standing record of calibration can be provided for all the lab's equipment.

Attention to detail is key in ensuring high accuracy across the broad range of frequencies and currents, and the lab features custom-made wire harnesses, specifically-designed multiplexers to cope with higher-frequency demands and three specialist power meters - one for up to 30A, one for as low as 1mA and one for 1.5V. Customers are provided with an array of data following calibration, with 40 individual measurements provided for each of the 100+ calibration points. Expert help is on hand, aiding understanding, and custom calibrations as well as custom calibration points can be requested.

Yokogawa has invested significant time and effort in achieving ISO17025 accreditation, with the process taking three and a half years, hundreds of documents and thousands of individual measurements, from start to finish. The accreditation, awarded by the Dutch RVA (Raad voor Accreditatie, or Accreditation Council), can be viewed on the RVA website here or downloaded at the foot of this article.

Laboratory manager Erik Kroon in situ (left) and a custom coaxial wire harness designed to minimise crosstalk at higher frequencies (right)

A business built on quality, repeatability and trust, Yokogawa's reputation and commitment to precision allows engineers to breathe easily. All instruments are provided with hard evidence to prove that they operate within their specifications, a capability dependent on the high-quality, in-house calibration facility at the company's disposal. Thanks to the accreditation Yokogawa can confirm, for example, that its WT3000E device (main picture) is the most accurate power analyser on the market.

Hailed by the company as "an essential development tool for the future,” the laboratory will ensure that all Yokogawa products have undergone the most rigorous compliance testing and certification before release. Full accreditable traceability is also offered, allowing customers to avoid time-consuming use of national laboratories.

“The fact that the European Standards Laboratory can offer up to 100kHz of accredited traceable power calibration puts us in a unique position in the market, and ISO17025 accreditation is the recognised international standard which enables us to justify these claims,” confirmed Marrinan. “The ability to offer both accredited calibration and be able to explain its relevance- particularly at higher frequencies - demonstrates that Yokogawa are the experts in power measurement and that Yokogawa power meters are truly the most accurate in the world.”

The laboratory offers systems for calibrating oscilloscopes, recorders and optical products, as well as wideband and high-accuracy power meter calibration systems.