Unidata supplies three evaporation systems that, taken together, cover nearly all evaporation measurement applications. The simplest is a manually operated unit while the most sophisticated is automated to the point where it requires only infrequent intervention by an operator.
All Unidata’s evaporation systems measure how much water evaporates from a US Class A evaporation pan by measuring the water level in an adjoining stillwell. Using a stillwell reduces the impact of fluctuations in the pan’s water level caused by wind.
The water level in the stillwell is measured using a modified Model 6541 Water Level Instrument. This arrangement delivers measurements with a resolution of 0.5mm. A thermistor probe float assembly can rest on the surface of the water in the evaporation pan to obtain a surface temperature reading.
The simplest model, known as the 6529-1 Evaporation Monitoring System, is comprised of an evaporation pan with a bird and leaf cover and a manual measurement system. The 6529-2 Evaporation Recording System is similar to the 6529-1 but includes a 128k Micrologger and an LCD display that shows the current depth of the evaporation pan. The addition of the Micrologger means that you can record evaporation measurements over time and have access to its other features such as SDI-12 communications, intelligent battery supervision, a modem interface and all the programmability found in STARLOG Data Loggers.
The 6529-3 is a fully automated system designed to operate for long periods without maintenance. In addition to the features of the 6529-2, it has the ability to automatically refill and discharge water from the evaporation pan. This enables you to manage a water source such as storing and recycling rainwater. This option includes a small solar panel.
Connect a telemetry system to the Micrologger enables you to monitor data acquisition, re-program the unit, and check the health of the site, all from a remote location. Landline, cellular, and radio communication links are supported. It is up to you to determine which alternative is available and most cost effective at the installation site. Using the telemetry feature decreases the need for time consuming site visits.
Remember that when you use one of the telemetry options you will probably need to provide external power such as a solar panel, external battery and regulator and use a larger enclosure.
A water temperature sensor and a range of weather sensors can be added to help identify the relationship between evaporation and other site conditions. Typically these are required for evaporation and evapotranspiration studies and modelling.
|
