The two modes on WeatherTRAK controllers that use Evapotranspiration (ET) are Auto (Automated by WeatherTRAK) and User with ET. This article explains the differences between these two modes.
Auto Mode (Automated by WeatherTRAK)
Rather than programming a schedule of days and minutes into your controller as is the case with conventional controllers, Auto (Automated by WeatherTRAK) uses ET to determine when and how much to irrigate during the scheduled water window. Evapotranspiration (ET), is the amount of water a plant loses based on temperature, wind, solar radiation, and humidity. Programmed variables like plant type, soil type, sprinkler type, and slope are factored in for each station to calculate runtimes that will efficiently meet your plant's needs and replace lost water.
When the controller receives its daily ET information, it will combine that ET value with the landscape variables for each station. It then calculates how fast that station’s soil is drying out along with how much moisture has evaporated out of the ground on any given day. When the maximum allowed depletion (MAD) level is reached for any station, the controller is scheduled for irrigation during the next available water window.
User with ET
Programming a station in User with ET allows you to program in a number of minutes per cycle and number of cycles per day, just like a User no ET or manual program. The difference is that reference ET and weekly ET numbers are used to adjust watering. The reference ET is a historical number based on location and time of year. The weekly ET is an average number based on current weather.
Irrigation will still occur at the times you programmed in; however, runtimes may vary, if the reference ET and weekly ET do not match. While in this mode, you will be getting all the benefits ET has to offer, while having the flexibility to choose start times and runtimes.
Equal ET: If the current weekly ET matches the station reference ET (normal weather) then the station will deliver exactly the runtime that is programmed.
High ET: If the current weekly ET is higher than the station reference ET (hotter weather) then the station runtime will be turned up in response.
Low ET: If the current weekly ET is lower than the station reference ET (cooler weather) then the station runtime will be turned down in response.
For instructions on how to program your controller in User with ET, read: Programming in User with ET Mode.