Sap Flow Sensors
The SF-4M and SF-5M sensors are designed for monitoring relative variations of sap flow rate in leaf petiole or small stem. The sensor is made as a hollow collapsible heat-insulating cylinder. A spring loaded heater and a thermopile are located inside the cylinder.
SF-type sensors provide recording of relative variations of sap flow rate
The operation of SF-4/5 sensors is based on a constant heat method with symmetric disposition of thermo-sensitive elements. A small heater warms a part of a stem 2—3 degrees above ambient temperature. Both junctions of the thermopile are located at identical distance above and below the heater. If there is no sap flow in the stem, the distribution of temperature is symmetric, and the output signal of the thermopile is close to zero. As a result of xylem flux, the temperature increases in the direction of the flow and decreases in the opposite direction. The thermopile output follows the gradient of temperature. However, the proportionality between sap flow rate and the thermopile signal is limited. Estimated upper limit is about 3 ml/h. Therefore, the sensor should be positioned on a stem so that the maximum possible sap flow rate does not exceed the limit specified above. It means that the area of leaves above the sensor should not exceed approximately 150 square centimeters. A leaf petiole is one of the most suitable places for application.
The SF sensors are sensitive to external heating. Therefore, it is highly recommended to protect the sensor by 2—3 layers of aluminum foil.
It is important to note that the SF-type sensors provide recording of relative variations of sap flow rate.
All SF-type sensors are tested on the water filled hose within the approximate measuring range.
Standard cable length between sensor and signal conditioner is 1 meter.
Sensor Specification
SF-4M
Overall dimensions of the sensor, mm 30 × 30 × 40
Suitable stem diameter, mm 1 to 5
SF-5M
Overall dimensions of the sensor, mm 30 × 35 × 40
Suitable stem diameter, mm 4 to 10
General Specification
Measurement range < 3 ml/h1
Output
Standard 0 to 2 VDC, linear
Optional 4 to 20 or 0 to 20 mA
Supply voltage 10 to 30 VDC @ 1 W max
Accuracy Not specified
Heating power (typical) 30 mW
Warm up time 5 min
Supply voltage 10 to 30 VDC @ 1 W max
Ordering Information
SF-4M Sap Flow Sensor Suitable stem diameter, mm 1 to 5
SF-5M Sap Flow Sensor Suitable stem diameter, mm 4 to 10
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