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Anemometer Calibration Update - New Wind Tunnel Facility January 2013

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As you may know, our long-time vendor, Otech Engineering, closed their wind tunnel and is no longer performing calibration services. Otech Engineering, founded and directed by John Obermeier, has been a leader in providing calibration services to the global wind energy industry. We congratulate John and Otech on their remarkable 31 years of business.


NRG Systems will begin calibrating our #40C and Class 1 anemometers at the new and completely independent wind tunnel based in Williston, Vermont (USA), SOH Wind Engineering LLC. SOH is led by wind engineering pioneer Svend Ole Hansen and will operate one of the world?s largest wind tunnels specializing in calibrations. Mr. Hansen?s existing wind tunnel in Copenhagen will continue to operate, enabling SOH to perform the highest quality calibrations on either side of the Atlantic.


We have been planning this transition for quite some time and have prepared the following Frequently Asked Questions.


When did Otech Close?

  • End of October, 2012

Why did Otech Close?

  • Otech Engineering will still be performing some consultancy work but have closed their wind tunnel.

Can we still buy calibrated anemometers, and if so, which models?

  • Yes - you can still buy calibrated anemometers.  As before, NRG Systems offers the following calibrated anemometers:
    • NRG #40C Anemometer
    • NRG Class 1 Anemometer
    • NRG GS-Class 1 Anemometer
    • WindSensor P2546C Anemometers
    • Hybrid  Anemometer
    • IceFree3 Anemometer
    • NRG 40H Anemometer

When did the new SOH Wind Engineering facility open?

  • This new facility became operational in Q4 2012, and calibrations for NRG Systems anemometers began January 2013.

How can I identify which tunnel was used to calibrate a particular sensor?

  •  The best way to identify the calibration tunnel used is to download the sensor calibration report from the NRG Technical Support webpage.   Each calibration report identifies the test facility and all relevant parameters.
  • The first sensor calibrated in the new facility shipped from NRG January 30, 2013 and had serial number 179500213300.  

What are the differences between the SOH Wind Engineering, SOH Denmark, and the Otech tunnel facilities?

  • Size - specifically the size of the cross-sectional area of the test section is the main difference between the three tunnels.  The tunnel cross sections are:
    • Otech (0.61 X 0.61m)
    • SOH ApS: 4-16 m/s calibration (1.7m X 1.2m),  4-26 m/s calibration (1.7m X 0.6m)
    • SOH Wind Engineering (3m X 3m)
  • The size of the wind tunnel test section matters because the uncertainty of the calibration is reduced with increased tunnel cross section.  The large 3m X 3m tunnel cross section of the new SOH wind tunnels will eliminate blockage effects, a known systematic bias that increases the uncertainty of anemometer calibrations.

What is NRG Systems relationship with the new facility?   Does NRG own the new tunnel facility?

  • NRG Systems has no ownership stake in the new tunnel facility; it is independently operated by SOH Wind Engineering.  It is in NRG Systems' interest to achieve the most accurate anemometer calibrations for our sensors so the total anemometer uncertainty is minimized, helping our customers achieve their goal of reducing overall uncertainty.

Is SOH Wind Engineering (USA) a member of MEASNET ?

  • Yes - The SOH Wind Engineering laboratory acheived MEASNET membership March of 2015.


What is MEASNET ?

  • MEASNET stands for the Measuring Network of Wind Energy Institutes. In simple terms, it is a group of commercial institutions who continuously collaborate to ensure that each member offers measurements of equally high quality for the worldwide industry.

What are the capabilities of the new facility?

  • The SOH Wind Engineering facility currently contains two parallel tunnels and two more will be added, each having a 3m X 3m cross section.  The tunnels can be combined to create a larger test section of up to 12m X 3m.
  • At the 3m x 3m cross-sectional size, the tunnels will be capable of producing wind velocities of up to 20 meters per second, with capabilities up to 100 meters per second using smaller cross-sections.  For example a 2.5m x 2.5m insert will allow speeds up to 28 meters per second.

How does the facility performance compare to other calibration facilities?

  • The SOH Wind Engineering wind tunnel is one of the largest calibration wind tunnels in the world which means the effects of blockage are truly negligible.  Because the effects of blockage are negligible, the calibration uncertainty is minimized relative to smaller tunnels.

What is the new consensus transfer function?

  • The consensus transfer function remains unchanged.  It was derived from consensus wind tunnel data in 1998 and remains an excellent predictor of the output of the NRG #40C Anemometer.  The user may decide whether to use the consensus transfer function or the individual slope and offset calibration values.

What international standards does the SOH Wind Engineering facility follow?

  • ISO 17025 "General requirements for the competence of testing and calibration laboratories" is the main internationally recognized standard for establishing and maintaining a Quality Management System for calibration facilities.  The SOH Wind Engineering facility achieved ISO 17025 accreditation December 2012.


I purchased SOH WE-calibrated sensors calibrated before the MEASNET certification was finalized. Has the calibration process changed?

  • The calibration procedure has not changed. SOH WE has been using the same calibration procedure used by MEASNET since opening in 2013 (IEC 61400-12-1 Annex F). This change simply means that anemometers calibrated at SOH WE are now officially certified by MEASNET.


Will I still be able to purchase sensors from the SOH Copenhagen tunnel?

  • Yes, RNRG will still offer MEASNET anemometers calibrated at the SOH Copenhagen site on an as-needed basis.


Who can I talk to in order to learn more about the new calibration facility technical details?

  • NRG Technical Support ? support@nrgsystems.com

Should we talk with SOH directly using the contact info on the SOH website?

  • NRG Technical Support and Sales continue to be the main point-of-contact for all anemometer calibrations and can answer your questions.
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