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johng

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  1. Sad
    johng got a reaction from dapedlen in NRG item 4214 -- new 95" sensor mounting boom   
    Great Question!
    The short answer is that the new 95 inch boom can be used in applications
    which require lower measurement uncertainty than the 60 inch boom. 
    As for the long answer... 


    I believe you might be looking at Figure G.5 in IEC 61400-12-1 which is
    based on 2 dimensional Navier-Stokes computations.



    If so, the figures you indicate are about right (4 tower diameters equates
    to about a 2.3% centerline disturbance). 
    Another consideration is that the IEC model measures the offset distance
    as tower centerline to sensor centerline, which really places the 60 inch boom
    at about 6.5 diameters (for a 10 inch tower) equating to a centerline
    disturbance of about 1%.



    However, here is another way to look at it...what level of disturbance is
    acceptable for your wind resource assessment campaign?



    Many in the industry would say "let?s make it 0.00%!"...



    Basically, the further the sensor is away from the tower, the lower the
    disturbance.  In reality, the law of
    diminishing returns comes into play and no matter how long a boom is
    (realistically) the disturbance will not (in theory) be 0.00%.  At about
    10 diameters, the disturbance curve flattens out and approaches
    horizontal.  This is really the sweet spot of boom design as the
    centerline disturbance is less than 0.5% (some might say it is about 0.3% but I
    prefer to be a bit conservative).  I have
    also heard that some in the industry believe disturbances are actually greater
    than what the Navier-Stokes model predicts. 
    If anyone has seen research papers in this area, please add links to
    this thread!



    Of course, other design factors are involved such as robustness, cost, ease
    of installation and transport (the new booms are cost effective, easy to
    install and are also UPS shippable).



    In summary, NRG will continue to offer both the 60 inch boom and the 95 inch
    boom.  The new 95 inch boom can be used in applications
    which require lower measurement uncertainty than the 60 inch boom.



     



  2. Like
    johng got a reaction from ritaSn in How do I interpret the SDR wind rose report?   
    See the example PDF above...
     
    The extension of each bar in the wind rose from ?inner
    circle? towards ?outer circle? represents the percentage of the time the wind
    blew from those various directions. 
     
    The outer circle percentage indicates
    the amount of relative uniformity of the wind direction.  For example, if
    there was a very strange site where the wind only blew from one direction all
    the time, and never from any other direction, there would be a single bar going
    out from 0 to 100%.  Most sites, however, have more scatter with wind
    directions distributed among numerous directions. 
     
    All of the bars
    extending out will of course add up to 100% of the time period that was
    measured.  The ?outer circle? value is intended to provide some context
    for the graph so that at a quick glance, you can tell that at the site below,
    almost 30% of the time, the wind direction was southwest, another 25% or so was
    north, and then the rest of the directions are distributed among the other
    directions to add up to the remaining 45%.
     
     
    windrose-sample-report.pdf
  3. Like
    johng got a reaction from ritaSn in Formatting an NRG-supplied SD Card for SymphoniePLUS3   
    The attached note which explains how to format an NRG-supplied SD card using a Windows 7 computer and SD card reader.

     

     
    TSB011_SymphoniePLUS3_SDCard_Formatting.pdf
  4. Like
    johng got a reaction from ritaSn in Protection of Wiring in Marine Environments   
    For additional corrosion protection of your logger and sensor wiring, applying a
    petroleum jelly (Vaseline, non-corrosive) to all of the sensor and
    logger terminals can be effective.  

    Other options include commonly available dielectric grease which is purpose made for preventing corrosion of electrical connections.  The grease is non-conductive (so there is no need to worry about electrical leakage or shorts), is very slippery and available at auto parts stores.
    One such example is: http://www.jamestowndistributors.com/userportal/show_product.do?pid=8196 


     
     



  5. Like
    johng got a reaction from SementhilK in Protection of Wiring in Marine Environments   
    For additional corrosion protection of your logger and sensor wiring, applying a
    petroleum jelly (Vaseline, non-corrosive) to all of the sensor and
    logger terminals can be effective.  

    Other options include commonly available dielectric grease which is purpose made for preventing corrosion of electrical connections.  The grease is non-conductive (so there is no need to worry about electrical leakage or shorts), is very slippery and available at auto parts stores.
    One such example is: http://www.jamestowndistributors.com/userportal/show_product.do?pid=8196 


     
     



  6. Like
    johng got a reaction from SementhilK in How do I interpret the SDR wind rose report?   
    See the example PDF above...
     
    The extension of each bar in the wind rose from ?inner
    circle? towards ?outer circle? represents the percentage of the time the wind
    blew from those various directions. 
     
    The outer circle percentage indicates
    the amount of relative uniformity of the wind direction.  For example, if
    there was a very strange site where the wind only blew from one direction all
    the time, and never from any other direction, there would be a single bar going
    out from 0 to 100%.  Most sites, however, have more scatter with wind
    directions distributed among numerous directions. 
     
    All of the bars
    extending out will of course add up to 100% of the time period that was
    measured.  The ?outer circle? value is intended to provide some context
    for the graph so that at a quick glance, you can tell that at the site below,
    almost 30% of the time, the wind direction was southwest, another 25% or so was
    north, and then the rest of the directions are distributed among the other
    directions to add up to the remaining 45%.
     
     
    windrose-sample-report.pdf
  7. Like
    johng got a reaction from JeremyNuh in Formatting an NRG-supplied SD Card for SymphoniePLUS3   
    The attached note which explains how to format an NRG-supplied SD card using a Windows 7 computer and SD card reader.

     

     
    TSB011_SymphoniePLUS3_SDCard_Formatting.pdf
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