For some time now we have been studying and checking NRG #40 anemometer tolerances and manufacturing processes in tremendous detail to understand what has been causing some of the sensors to intermittently underreport wind speed.
Recently we reported that a vibratory mode had been identified as the cause of the slow down. As a result of our analysis and testing, we have revised the specifications of certain materials and tightened the tolerances of certain dimensions of the sensor. These improvements have eliminated the vibratory mode in test sensors in our laboratory. We have further validated these improvements in wind tunnel tests and in limited field tests. Final validation of these improvements must await the results of longer term field data which will take another 6 to eight weeks.
We are confident, based upon the results of our laboratory testing, that these changes have a high potential to significantly reduce the probability that a sensor will degrade in the field. Therefore, we believe that it is appropriate to integrate these modifications into the NRG#40 immediately. As of January 5, 2009, all sensors will ship with the improvements.