Apogee Instruments SI-121 Owner's Manual - Page 16
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MAINTENANCE AND RECALIBRATION
Blocking of the optical path between the target and detector, often due to moisture or debris on the filter, is a
common cause of inaccurate measurements. The filter in SI series radiometers is inset in an aperture, but can
become partially blocked in four ways:
1.
Dew or frost formation on the filter.
2.
Salt deposit accumulation on the filter, due to evaporating irrigation water or sea spray. This leaves a thin
white film on the filter surface. Salt deposits can be removed with a dilute acid (e.g., vinegar). Salt
deposits cannot be removed with solvents such as alcohol or acetone.
3.
Dust and dirt deposition in the aperture and on the filter (usually a larger problem in windy
environments). Dust and dirt are best removed with deionized water, rubbing alcohol, or in extreme
cases, acetone.
4. Spiders/insects and/or nests in the aperture leading to the filter. If spiders/insects are a problem,
repellent should be applied around the aperture entrance (not on the filter).
Clean inner threads of the aperture and the filter with a cotton swab dipped in the appropriate solvent. Never use
an abrasive material on the filter. Use only gentle pressure when cleaning the filter with a cotton swab, to avoid
scratching the outer surface. The solvent should be allowed to do the cleaning, not mechanical force.
It is recommended that infrared radiometers be recalibrated every two years. See the Apogee webpage for details
regarding return of sensors for recalibration
repairs/).
(http://www.apogeeinstruments.com/tech-support-recalibration-