Soil moisture measurement at different ground depths with Internet data transmission
In fruit and grape growing, as well as in other areas of agriculture, the produce has to meet ever higher quality criteria. To continually ensure that standards are met, technical aids that can measure every environmental factor are being used with increasing frequency. Optimizing irrigation systems help to maximize yields and minimize costs, as a uniform level of moisture in the soil during the growing period results in optimal growth and so to a better quality harvest.
Moisture levels can be measured very accurately using the BFS-40 soil moisture sensor, allowing the appropriate action to be taken. The sensor is simply pushed into the ground so that the moisture content can be determined at different depths.
Mode of Operation
The individual measuring cells in the BFS-40 soil moisture sensor create a continuous electrical field at four different depths. This field is then influenced by the water content of the soil. The measuring cells are located at 10, 30, 50 and 80 cm deep. The integrated 32-bit microprocessor then calculates the resulting moisture and adjusts this to the conditions, by scaling the moisture value relative to the measured minimum and maximum. This data is saved in an integrated buffer and, depending on the model, made available via a serial interface or web server. The reaction time is normally in the region of a few seconds (see Fig. 1)
Communication with the soil moisture sensor is via an internet connection using the integrated GPRS module (SIM card required) or RS485 interface. The sensor can be configured using appropriate SMS commands. All readings are sent periodically to the Elmed web server via the internet connection. They can be accessed via the Elmed web interface and are shown in chart form.
The following additional sensors can be connected to the BFS-40 sensor by means of the integrated plug connection:
- Leaf moisture sensor
- Rainfall sensor
- PPressure switch for detecting sprinkler irrigation
- Solar panel
The BFS-40 soil moisture sensor consists of a cylindrical PVC tube with a component attached to the top. The component at the top contains all of the electronics including the GPRS module and antenna, plus a 7-pin plug socket that is accessible from the outside. Inside the top component there is also a 2600 mAh Li-ion battery which powers the system autonomously. A 5W solar panel is connected to the integrated charging electronics via the plug socket.
The sensor is installed by preparing a bore hole using a special drill in the field. It is important not to destroy the soil composition by drilling the bore hole incorrectly, as this will prevent the electric field from spreading uniformly. The sensor can be protected from mechanical damage by applying a protective cap. Condensation is able to pass through unimpeded.
|Measuring principle:||electrical field, capacitive|
|Reaction time:||depending on soil composition, in the region of a few seconds|
|Number of sensors:||4 sensors at 10cm, 30cm, 50cm and 80cm deep|
|Total length of sensor:||106.5 cm|
|Length of cylinder tube:||99cm|
|Diameter of sensor head:||120mm|
|Diameter of the cylinder tube:||40mm|
|Housing:||PC-ABS RAL7035, UV resistant|
|Power supply via cablel:||9-18V DC|
|Battery charging current:||max. 225mA|
|Battery capacity:||2600mAh (type)|
|Battery technology:||3-cell lithium ion with protective circuitry|
|Charging characteristic:||PWM CCCV|
|Current consumption - standby:||0.66 mA|
|Current consumption at undervoltage:||0.13 mA|
|Total discharge protection:||<8.1V|
|Output signal:||serial bus RS485|
|Data transmission:||via GPRS or wireless LAN (on request)|