ADU-500 Collects Reliable Soil Moisture Measurements
Accurate soil moisture content is an important parameter in a number of applications including geologists studying landslide potential, civil engineers designing watersheds or the National Weather Center predicting floods. But, probably the most widespread use is in agricultural studies designed to optimize crop quality and improve field yield so we can continue to feed the earth’s growing population with the limited land and resources available. CAS DataLoggers focuses on how the Infinite Informatics ADU-500 Autonomous RTU Data Logger captures the required data through its SDI-12 and channels at a remote location. Using its built-in cellular modem, the ADU-500 can transmit the stored data via FTP and can also send alerts via SMS when measurements are outside of the desired range for reliable soil moisture monitoring.
Soil Moisture Monitoring Measurements
Soil moisture monitoring is important in agriculture to help farmers manage irrigation systems more efficiently allowing them to use less water while increasing yields. When soil moisture data is compared to the environmental data farmers can predict how much water will be needed at any time to maximize plant growth during various stages of growth. Soil moisture sensors commonly use the SDI-12 serial protocol, allowing multiple sensors to connect to the data logger via a single cable.
In addition to soil moisture, some of these sensors can also measure the electrical conductivity of the soil. The conductivity is related to the salinity level in the soil. These measurements are important because the level of salt in soil moisture has dramatic effects on crop health and yields because agricultural soils may become sodic (higher Sodium than usual). There are techniques that can remove the sodium to improve soil quality and increase crop production but identifying where these soil conditions are and when they occur are a challenge to say the least.
There are 3 main methods used to measure soil moisture content and electrical conductivity. Time Domain Reflectometry (TDR) identifies the presence of various substances by sending out an electric signal and measuring how long it takes to receive the signal back. Time Domain Transmissometry (TDT) is similar to TDR except that a pulse of electricity is used rather than a continuous signal from a closed loop. Frequency Domain Reflectometry (FDR) is similar to TDR and TDT except that the amplitude response of the sensor signal is measured and Coaxial Impedance Dielectric Reflectometry (CIDR) is an FDR sensor that measures the frequency response of the outgoing signal to determine conductivity.
ADU-500 Application Case Study
In this application, an ADU-500 is used to measure and record air temperature, humidity, precipitation and soil moisture. The ultra-low power Vaisala HMP60 sensor is used to measure air temperature and humidity. A Texas Weather Instruments TR-525U tipping bucket rain gauge is connected to the digital counter for precipitation data, and 6 soil moisture sensors are connected to the SDI-12 port measuring soil moisture via conductivity at various soil depths. The ADU-500 RTU performs data collection according to the selected sampling rate of once every 15 minutes. Using the built-in 3G cell modem, recorded data is sent daily via FTP to a server where it is processed and archived. Alarm events, for example unusually high precipitation rates, initiate SMS text messages that are sent to predefined users so they can take corrective action if necessary.
The Infinite ADU-500 is an autonomous data logger\RTU (remote telemetry unit) that can record data from up to 2 analog sensors and 3 digital inputs plus several SDI-12 sensors up to a total of 48 measurement channels which provides a flexible cost-effective platform for remote data logging applications. Powered only by the internal 3.6V Lithium Thionyl battery, it can provide voltage excitation from 3.3 to 12 VDC for the analog and SDI-12 sensors.
The Lithium Thionyl battery lifetime is calculated for different several different SDI-12 soil moisture sensor types below:
Hydra Probe II
5TE / GS3
|Nr. of sensors|
10 / 25
|Warm up time [sec]|
|Measurement time [sec]|
|Battery Lifetime [Years]1)|
5 / 4
For further information on the ADU-500 Autonomous RTU Data Logger, soil moisture monitoring, or to find the ideal solution for your application-specific needs, contact a CAS Data Logger Application Specialist at (800) 956-4437 or request more information.