Small Stem Sap Flow Sensor

Stem Sap Flow Sensor.



The SF-4M and SF-5M Sap Flow Sensors should only be used in indoor areas such as glasshouses, grow tunnels and growth cabinets.


  • Measure stems between 1 and 10 mm diameter;
  • Clip on sensor that is easy to install in seconds;
  • High frequency data logging over seconds to minutes;
  • SDI-12 protocol or optional voltage / 4..20mA output;
  • Calibrate for sap flow or stomatal conductance.


Measuring sap flow in small stems, petioles, flower or fruit pedicel or peduncle is vastly challenging. Our sap flow sensors have met this challenge. The SF-4M and SF-5M are the product of over 50 years of sap flow research and allow plant physiologists to measure, and monitor, sap flow on small diameter stems.

The SF-4M model is suitable for stems, petioles, pedicels or peduncles with diameters between 1mm and 5mm. The SF-5M model is suitable for stems, petioles, pedicels or peduncles with diameters between 4mm and 10mm.

The sensor’s probe is made as a hollow collapsible heat-insulating cylinder. A heater and a pair of bead thermistors are located inside the cylinder. A signal conditioner provides powering of the heater and conditioning of the output signal.

The probe is connected by a standard 1-meter cable to the waterproof box with the signal conditioner inside. The output cable length should be specified in the order if required. The SF-4M and SF-5M are connected to our range of data logging systems. Alternatively, we can assist you in connect the sap flow sensors to your existing data logging system.

We also provides training, assistance with installation, and on-going assistance with data interpretation and analysis.


Sap Flow Calibration

The calibration slopes for three different species. Blue circles: Hakea (R2 = 0.90, p < 0.05); Red circles: Ardisia (R2 = 0.76, p < 0.05); Pink circles: Fragaria (R2 = 0.82, p < 0.05).

Calibration of the SF-4/5

The output from the SF-4/5 is given in raw, or millivolt (mV), values. There is a direct and linear relationship between mV output and sap flow or plant water use. Individual sensors can be calibrated for different species if the parameter of interest is sap flow (kg/hr) or plant water use (mmol per m2 per second). The graph to the right shows an example calibration between a SF-4 sensor and a three different species with small plant stems.



The Sap Flow Method

The SF-4M and SF-5M sap flow sensors are a modification of the thermal dissipation method (TDM) with symmetrical allocation of temperature sensors in relation to the heater. In classical Granier TDM sensor, the upper temperature sensor is located in the heater. Therefore, the temperature difference is maximal at no flow. In our sensor, the temperature difference is zero at no flow, and it is increasing with the sap flow acceleration. Also the output signal is sensitive to the direction of the flow.

Dr Yuri Ton, and his team at Phyto Sensor Group, developed the SF-4M and SF-5M from industrial water flow measurement methods, and from sap flow sensors designed by Russian scientist V. Karmanov in 1959. The signal from the sap flow sensors is positive, zero or negative, depending on the direction of flow. The higher the flow, the greater the output signal. With small scale lysimeters, the output signal can be calibrated to give volumetric sap flow and transpiration rates for specific plant species and organs. Alternatively, data can be analysed as a proportion of maximum sap flow. That is, maximum sap flow, or the highest output voltage signal, is 100% sap flow and all remaining data are corrected against this value.


Sap Flow SystemSap Flow Systems

Edaphic Scientific can build and develop a sap flow monitoring system for your research project. The system is flexible and can combine the SF-4/5 Sap Flow Sensors with related parameters such as soil moisture, vapour pressure deficit (VPD), temperature, humidity, rainfall and other meteorological parameters.

Each system is custom designed and built to meet your specific research requirements. Contact the scientists and engineers at Edaphic Scientific for more information.


Continuous Stomatal Conductance Measurements

The SF-4M or SF-5M sap flow sensors can be installed on petioles of leaves. The sensors can then be calibrated against a stomatal conductance instrument such as a porometer.

Linear regression analyses have shown the the output from the SF-4M or SF-5M sap flow sensors are strongly correlated with stomatal conductance measurements with R² values > 0.95.

Although the SF-4M and SF-5M sensors are measuring sap flow through the petiole, the tight correlation with stomatal conductance means it is also possible to measure stomatal conductance continuously. This has a significant advantage over existing meters, such as the LiCor instrument or the SC-1 Leaf Porometer, that are usually manually operated and are difficult to obtain continuous data.

Visit this website for more information on how to use the SF-4M or SF-5M as a continuous stomatal conductance sensor.




Feature Specification
Measurement Range 0 to 100 % sap flow
Output SDI-12 | 0 to 2 VDC | 4..20mA
Supply Voltage 10 to 30 VDC
Accuracy Individual species/specimen calibration recommended
Heat Power 30 mW (typical)
Suitable Stem Diameter SF-4M: 1 to 5 mm | SF-5M: 4 to 10 mm
Warm Up Time 5 minutes
Maximum Measurement Frequency 1 second following 5 minute warm up period
Sensor Dimensions SF-4M: 30 x 30 x 40 mm | SF-5M: 30 x 35 x 40 mm
Cable Length Between Probe and Conditioning Box 1 m
Cable Length Between Conditioning Box and Logger 5 m (standard) | SDI-12 max: 60 m | Voltage max: 10 m | 4..20mA max: 200 m
Warranty 1 year

Manual & Docs

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