Programming instructions

Designer’s Guide 35
Calsense
Weather Sensors
ET Gage (model ETG)
Using a Calsense ET Gage, ET2000e Irrigation Controllers can use real-time daily ET to calculate station
run times automatically. To connect to an ET Gage, the controller must be specified to include the -G
interface. The ET Gage is designed to evaporate water at the same rate as tall fescue (Figure 14
).
Measurements comparing the ET Gage to weather stations computing ET using the Penman-Monteith
evapotranspiration formula show better than 95% accuracy.
The ET Gage sends daily ET numbers to the ET2000e Irrigation Controller, which stores the last 28 days of
ET. When it comes time to irrigate a station, the controller tallies the ET numbers since the last irrigation.
For example, if it has been three days since the ET2000e irrigated, it will total the first three numbers in
the table. The controller then multiplies this number by the station’s ET factor, which is used to adjust for
irrigation efficiency and crop type, to calculate how much water to apply. Then, using the station’s
precipitation rate, the run time is calculated. If there is no signal from the ET Gage, historical ET data is
substituted.
Figure 14 - ET Gage installed in Vandal-Resistant Enclosure