Instrumentation and control engineering for industry and agriculture

BFS-40 Soil Moisture Sensor

Soil moisture measurement at different ground depths with Internet data transmission
Item 46-46-151

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)

Peripherals

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

Structure

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.

Assembly

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.

Technical Data

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
Weight: 1200g
Power supply via cablel: 9-18V DC
Battery charging current: max. 225mA
Battery voltage: 11.1V
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
Undervoltage shut-off: <9.2V
Total discharge protection: <8.1V
Overvoltage protection: >13V
Charging initiated: >10V
Output signal: serial bus RS485
Data transmission: via GPRS or wireless LAN (on request)

Accessories (optional):

44·44·335 Leaf moisture sensor adjustable: 0–100 %  
41·41·66 Rainfall sensor resolution 0.1 mm  
4·34·153 Pressure switch 1-5bar  
46·46·169 Protective cap in PVS d=16cm, h=50cm  
45·45·65 Solar panel 5W, 17.5V, LxW 34x20cm  
54·54·07 Drill with handle for installation d=42mm, l=102cm  
56·56·33 Bracket for rainfall sensor    
56·56·34

Bracket for leaf moisture sensor
with socket

   
46·46·143

BF-40 soil moisture sensor
with RS485 interface

4 Sensoren 10, 30, 50, 80cm  
36·36·278

Software "MeteoWeb"