Start Date | Start Time | End Date | End Time | Data Quality Metric |
---|---|---|---|---|
12/23/2005 | 0000 | 02/23/2006 | 0800 | Suspect |
Subject: | NIM/SKYRAD/M1 - Instrument ventilator problem |
DataStreams: | nimskyrad60sM1.b1, nimskyrad20sM1.a0, nimskyradM1.00 |
Description: | Data quality office first reported that PIR1 and PIR2 appear to be deviating more than typical during the daylight hours. It was found that the Skyrad PIR ventilator fans were building up debris on the intake air filter. Obstructed air flow results in solar heating of the PIR ventilator housing in the later part of the day and biasing the incomming IR irradiance values. The slow buildup was insidious and wasn't discovered and corrected (i.e. ventilator fans cleaned on a regular and frequent basis) until Feb 23rd. On or around December 23rd was when this problem may have first started. We are unable to quantify the extent of the problem in W/m2. Normal deviation between PIRs is typically 3-5 W/m2. |
Suggestions: | There is no quantitative way to determine how far from truth the PIRs deviated due to enclosure heating. Avoid using PIR1,PIR2 data after midday to sunset or only when the difference between PIR1 and PIR2 is less than the specified uncertainty - typically 2-5W/m2 |
Measurements: | nimskyrad20sM1.a0: more
nimskyrad60sM1.b1: more nimskyradM1.00: more |