SGP/SIRS/E27 - incorrect tracking

The solar tracker at E27 was not functioning properly.  The problem affected tracker 
mounted instruments: downwelling diffuse 8-48 and direct normal pyrheliometer NIP.  

After tracker adjustment on 4/14/2004 1700GMT the tracker stopped tracking properly during 
afternoon hours.  Attempts to correct tracker operation throughout the failure period 
resulted in variations on incorrect tracker operation.  No replacement tracker was available.

After adjustment on 9/15/2004 the tracker problem was resolved.  It is unclear what, other 
than typical az and zen tracker software changes by field techs, corrected the problem.  
This problem period corresponds to the first time range specified (4/14 to 9/15). 

On 10/27/2004 a replacement tracker was installed at E27.  Technical difficulties kept 
tracker out of service until 11/05/2004. The replacement tracker at E27 was put into serice 
by the field techs on 11/05/2004 1830GMT.  The tracker has been tracking correctly since 
this time.  This problem period corresponds to the second time range (10/27 to 11/05).

disregard this data

• Instantaneous direct normal shortwave irradiance, pyrheliometer thermopile
  voltage(inst_direct_normal)
• Instantaneous uncorrected downwelling shortwave diffuse, shaded pyranometer
  thermopile voltage(inst_diffuse)

• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer(down_short_diffuse_hemisp)
• Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Downwelling shortwave diffuse hemispheric irradiance, pyranometer, maxima(down_short_diffuse_hemisp_max)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyrgeometer, Minima(down_short_diffuse_hemisp_min)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyranometer, Standard
  Deviation(down_short_diffuse_hemisp_std)
• Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)

• (Raw data stream - documentation not supported)