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Julia Austin

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Posts posted by Julia Austin

  1. Q: What is the root cause of the vibratory mode or mechanism that causes it to occur? Will the fix entail replacement of defective material or change to the manufacturing process?


    A: The root cause of the vibratory mode, the mechanism of how it occurs, and possible changes to the manufacturing process are facts we will readily share after successful field validation of the modified sensor.

  2. Q: Could you discuss the onset of the vibratory mode and time it takes to present itself? Could any sensor be impacted at any time in its life?

    A: Based largely on customer field data, we?ve found that pairs of sensors exhibit scatter as soon as 2 weeks and as late as 26 weeks. While sensors may enter the vibratory mode anywhere in this 2-26 week period, it is more likely to occur in the 2-6 week range.

  3. Q: Until you have new sensors to sell, what will you sell? Will NRG supply a different anemometer with tower orders until the problem is corrected?

    A: NRG continues to offer the #40C sensor for sale either as part of our complete NOW systems or stand alone. Many customers have continued to choose this sensor because it continues to provide usable data. As always, the data should be quality-checked, and depending upon the tower configuration, any potential slow-down can be mitigated through detailed analysis. The Symphonie data logger can support other types of anemometers. However we do not provide recommendations on specific manufacturers and leave that decision to customers.
     

  4.  Q: How far back does the historical data go and has there ever been a period when no sensor dragging existed? Is the target series of anemometers still the same? January 2006 or later?


    A:  The first report of sensor dragging was received in 2007. Review of data from the past five years indicates that this problem began in 2006.

  5. Q:  What anemometers will work with the Symphonie logger besides the #40? What anemometer does NRG recommend in lieu of the #40?


     


    A: There are a variety of anemometers that will work with the Symphonie logger.
     
    Consult NRG Systems Tech Support or your sales rep for details. We do not recommend one anemometer manufacturer over another. Every cup anemometer has its own strengths and weaknesses which need to be evaluated in light of the project.

  6. Q: When will I get another update?

     

    A: The webinar of 12/02/08 was part of ongoing communication. We will continue to provide other updates and opportunities to speak with our team as more information becomes available.  As always, please feel free to contact Sales or Technical Support directly via phone or through the Technical Forum on the web.

  7. Q: What are your success criteria for the validation of the revised design?

     

    A: We will determine success based on these three criteria:

    1. Data from field tests of 50 pairs of revised sensors do not exhibit excessive scatter or mean
       
      bias.
       
      Initial results will be assessed after one month with on-going testing.
       

    2. Customer review and acceptance of field results
       
    3. Validation of post-cal data

     

  8. Q: What role do booms play in the occurrence of #40 slow down? If you?re not ready to share the root cause, then how can you be so sure it?s NOT the boom?        

     

    A: The boom could contribute to the vibratory mode through coupling, but it is not part of the root cause.
     
    Sensor dragging has been observed on many different boom types. This is one factor that has led us to rule out the boom as the root cause.

     

     
  9. Q: Why has NRG continued to ship sensors that were possibly defective?

    A: There are five reasons:

    1. Prior to September we were not certain there was a problem with the sensor itself. While some believed the root cause to be boom vibration, our initial investigation told us this was likely not the case. That is why we continued to investigate the sensor itself.

    2. According to many of our customers, the data was still usable and was within the typical margin of testing error.
    3. Not all sensors exhibited dragging. Some customers reported no incidents, while others reported higher frequencies of incidents.
    4. Many variables contribute to uncertainty in wind measurement data (e.g. reference data, MCP methods, modeling, tower configuration, long term variability). Because the reported slow-down was a small piece of the whole, a piece that couldn?t be isolated, it did not make sense to pull the #40 from the market.
    5. After we identified the vibratory mode in September, we continued to ship sensors with all these factors in mind. Additionally, if we had pulled the #40, we would have taken huge capacity out of the industry.

     

  10. Q: If NRG can make sensors go bad in its new test lab, why not test all sensors before they leave NRG? Why continue to ship the current model if there is a test to screen for bad sensors?

     

     

    A: The lab test can reproduce the vibratory mode of sensors that have exhibited high scatter in the field, or by intentionally substituting problem parts in a new sensor. However, this test is unable to screen for future problems of normal production sensors.

     

  11. Q: If I have an effected sensor, how do I interpret my data? Do I scrap my existing data? Should I manipulate my data? What does NRG recommend doing to ensure reliable and accurate wind measurement data right now?

    A: The data should still be analyzed and scrutinized as one would normally do. Although additional uncertainty may exist, it can be accounted for and should be considered in the context of other sources of uncertainty (e.g. reference data, MCP methods, modeling, tower configuration, long term variability). We do not recommend any wholesale changes to equipment deployment and we continue to recommend installing sensor pairs at each level. It?s important to remember that, in most cases, sensor dragging leads to an under-reporting of wind speed, not an over-reporting.

     

  12. Hello, Sebastian - We've spoken with some customers who report no incidences and some who report very high incidences of affected anemometers.


    Based on all of the data that we?ve looked at, and all of the sensors we?ve looked at, it?s somewhere between 20% and 30%. We?ve had it reported as high as 100% by some customers. So we can only base that on looking at the entire population of sensors, and our best estimate is it is somewhere in that range.

     

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