Meteorology Sensors

Model 255 Series Evaporation Station

The 255 Series Evaporation Station is a complete systems used to measure the amount of water lost each day to evaporation. There are two commonly used procedures for making these measurements manually. In both, a Class A Evaporation Pan, 10 inches deep and 47.5 inches in diameter, holds the water and is normally installed on a wooden platform set on the ground in a grassy location.

One alternative for measuring the daily evaporation loss manually is to use a graduated hook gauge set on a stillwell to determine the water level in the pan. The hook gauge is adjusted until the point just breaks the water surface, and a reading is taken from the attached scale. The second alternative uses a stillwell with a fixed point. Each time a measurement is taken, the pan is refilled to the level of the point using a calibrated graduate. The graduate has a surface area of 1/100 that of the pan, so that the amount of water added is the equivalent evaporation. The choice between these alternatives is generally made on a practical basis, such as the availability of daily replacement water.

If automatic continuous evaporation recording is required, the 6541-11/C Precision Water Level Recorder can be set up beside and connected via a hose to the evaporation pan. Also available is an Automatic Refill System which provides a simple method to automatically refill an evaporation pan at specified times. It consists of an electronic water timer and an automatic float valve. The water timer switches on at a user-specified time, allowing water from an external gravity fed water source to flow into the pan. The float valve will stop the water flow at approximately 8-1/2" to 9-1/2" depending upon the water pressure. The timer then shuts off until the next programmed time.

The amount of evaporation is a function of temperature, humidity, wind, and other ambient conditions. In order to relate the evaporation to current or expected conditions, the maximum and minimum temperatures of the water and the amount of air passage are normally recorded along with evaporation.

Specifications