SF-G / SF-L Granier Sap Flow Sensors

Sap flow sensors are used to continuously measure water uptake in woody plants. The SF-G model corresponds to the classic, two-needle model developed in 1985 by André Granier.

Our four-needle SF-L sensor is an updated Granier sensor. The patented improvements correct the naturally occurring and time-varying vertical temperature gradients in the sapwood. Without correction (i.e. the original Granier sensor, SF-G) and despite isolation, these natural temperature gradients can lead to a temporary over- or underestimation of the measured sap flow values of up to 50% in extreme cases (cf. Do, F., & Rocheteau, A., 2002). Additional temperature measurements with the SF-L sensor enable a correction of the measured sap flow values, which prevents errors caused by the natural vertical stem temperature gradients. This results in a significantly higher accuracy and a stabler zero-point (ΔTmax) of the xylem (sap) flow.

A very helpful option to exactly determine this zero-point would be to use a dendrometer in order to continuously measure the water saturation level of the tree body. This additional measurement allows for a precise determination of zero sap flow conditions: sap flow = 0 if the relative humidity in the crown at 100% and the tree body is 100% saturated with water (no change in diameter according to the dendrometer data). The improved SF-L sensor combined with dendrometer-aided precise determination of zero flow conditions, makes a running nocturnal zeroing of the sap flow (according to Granier) unnecessary. This process enables the recording of a nocturnal xylem flow.


Specific to the SF-G model

  • Suitable for tree diameters > 1 cm

Specific to the SF-L model

  • Greater measurement accuracy
  • Correct determination of the xylem flow zero point when supplemented with dendrometer measurements
  • Allows measurement of nocturnal xylem flow
  • Additional information about tree growth provided by installing supplementary dendrometers


Specific to the SF-G model

  • The measured values are superimposed by naturally occurring vertical temperature fluctuations in the trunk (up to +/- 2.5 ° C). This leads to measurement errors greater than 50% and may impact the reliability of measurement results.
  • Nocturnal sap flow cannot be measured. Because of the temperature overlaps, nocturnal measurement values have to be set to zero.

Specific to the SF-L model

  • Not suitable for trees with a diameter < 8 cm
  • 3 logger channels are required per sensor


Model name

Suitable for diameters

Sensor needle // heater element length in mm

> 1 cm18 // 10

> 2 cm
33 // 20
43 // 20
63 // 20
SF-L> 8 cm18 // 10
33 // 20
43 // 20
63 // 20

Technical Data

Sensor model name

Sap Flow Sensor

Type SF-G

Type SF-G

Scope of application

For continuous measurement of the sap flow in wood plants

Suitable for diameter

> 1 cm

> 8 cm

Number of sensor needles



Sensor dimensions

Needle diameter: 1.5 mm;

Needle length//length heated in mm, available versions:

18//10; 33//20; 43//20; 63//20

Output signal

Analog, DC voltage -100µV to +800 µV

Required logger channels

1x differential, resolution better than 10 µV

3x differential, resolution better than 10 µV

Power supply

Sap flow sensors must be supplied via a constant current source (CCS). A CCS supplies up to 3 SF-G and / or SF-L sensors and continuously needs 85 mA x 12 V. This corresponds to 2.1 amps x hour / day.

Sensor cable length

5 m, extendable to max. 20 m


Technical data sheets

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Accessories & Compatible Products

Datenlogger and other accessories:

From small and compact to an extensive measuring network, Ecomatik offers complete system solutions for sensor data acquisition in any desired size:

In addition to a suitable data logger, a constant current source (CCS) is required for the operation of TDP sap flow sensors. The CCS can also be obtained from Ecomatik. If you order a complete TDP sap flow system, all the necessary components are already installed, wired and preconfigured in a logger box.


The output signal of TDP sap flow sensors is an analogue DC voltage in the range of -100 to 1000 μV. TDP sap flow sensors therefore require compatible data loggers with differential analog input channels and a voltage resolution of 10 μV or better. If you are unsure about the compatibility of an existing data logger, please do not hesitate to contact us.


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Your contact details and Assessment of your needs

Like so many things, everything started with an idea ...

In the case of the plant scientist and founder of ECOMATIK, Dr. Liu, it was the idea that modern measurement technology should enable crucial plant physiological parameters to be measured directly, precisely and with high temporal resolution on the plant itself. It was obvious to him that there is an information potential of immense value in the detailed understanding of immediate reactions of plants to their environment...