Today, Ventura County UCCE’s Maren Mochizuki explains the routine maintenance required to keep CIMIS weather stations functioning accurately.

Data from CIMIS stations, please see previous post for details, provide accurate weather data to aid growers in irrigation planning and scheduling.  To ensure that each individual station measures and records accurately, monthly maintenance is performed at all stations.

For the CIMIS station at the Hansen Agricultural Center in Santa Paula, Staff Research Associate Maren Mochizuki checks the functioning of all the sensors.  She also checks the calibration of the relative humidity sensor using a psychrometer.  A psychrometer has one thermometer exposed to ambient air and another thermometer attached to a wick that is saturated with distilled water; a battery-powered fan forces air past the wick to evaporate the water and cool the temperature measured by the thermometer.

Using a conversion table, we can estimate the relative humidity based on the difference between the ambient temperature and the wetted temperature.  Drier air means more evaporation and a larger temperature difference between the two thermometers.  If the difference between the relative humidity calculated by the psychrometer reading and the station sensor is greater than 5%, the station sensor requires re-calibration.  The station is an inviting perch for birds so we also hose it down monthly to keep it clean.

inside of CIMIS station

psychrometer