SGP/SIRS/E16 - NIP Instrument Failure

The short_direct_normal dropped below MIN value on 4/28/06 resulting in failure of the 
up_long_hemisp started 3-component test.  No data are available from 20060428.1900 through 
20060503.21:39.  When the data returned, the short_direct normal fluctuated wildly 
throughout the day, and down_long_hemisp & up_long_hemisp failed the 3-component test.  
Technicians determined the NIP had failed and replaced it 5/12.

Use component method ((global - diffuse)/cos(ZA)) to calculate direct normal. For more 
information on this summation method please see section 7.2 (Theory of Operation) of the 
SIRS Handbook:
http://www.arm.gov/publications/tech_reports/handbooks/sirs_handbook.pdf

Calculate direct normal as described below.

• Instantaneous direct normal shortwave irradiance, pyrheliometer thermopile
  voltage(inst_direct_normal)

• Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)
• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)