ET controllers and irrigation
The words of "evaporation" and "transpiration" are combined into "EvapoTranspiration" or ET. Water "evaporates" from the dirt. Plants use "transpiration" of soil moisture to cool themselves like humans use "perspiration". Plants also use water in photosynthesis. ET measures all these water losses from the landscape.

It is not practical to directly measure ET. So various state agencies have researched the correlation between weather data and ET. The picture below shows a weather station specifically designed to collect weather data for the purpose of estimating ET. This ET weather instrument is part of the California Irrigation Management Information Service (CIMIS).

ET controllers are irrigation controllers which use some method of weather based adjustment of irrigation. These adjusting methods include:

Accurate WeatherSet's ET controllers use on-site measurements of solar radiation, which is the dominant factor (85%) in ET computations, and on-site measurements of rainfall to adjust irrigation automatically to track weather....rain or shine !!! Accurate WeatherSet's ET controllers measure the SunFall™ and rainfall every second on your property which is as "real time" and "on-site" as it gets. There are no signal fees with Accurate WeatherSet products.

Use of historical ET to automatically change irrigation will save water. But, common-sense tells you that unusual weather will easily raise ET significantly above historical averages. Water is conserved, but plant stress is likely when using only historical averages.

AquaConserve and Weathermatic are 2 of several companies that base their control logic on historical measures of weather data.

Weathermatic's SmartLine ET controllers adjust their watering by varying historical starting points using temperature measurements.

AquaConserve's ET controllers are similar to Weathermatic's ET controllers. AquaConserve also uses a temperature sensor to modify the watering from historical dictates.

WeatherTrak (HydroPoint), Intelli-Sense and SmartDial ET controllers broadcast or webcast "real-time" weather data to remote controllers for a monthly fee are methods used by other controller. ET controllers that use this method include

The business model of these companies is similar to cable companies which insist on a monthly fee for the rest of your life for their broadcast service. These ET controllers require continuous monthly fees for proper functioning.

Business questions to consider before signing a contract to pay fees for ET signals:

List of the most important Studies done on ET controller, often time called "weather based irrigation controllers," click here

ET EveryWhere™ is trademark of HydroPoint Data Systems and SunFall™ is a trademark of Accurate WeatherSet.

ET weather stations measure

On average, 85% of ET is solar radiation and 10% is wind. When there is no wind, then solar radiation is 90-95% of ET.