SFM-5 Sap flow sensor

SFM-5 Sap flow sensor

Item no.: 1700601 (5 m cable)

Advantages at a glance

  • New compact and optimized version
  • Output of 33 different parameters
  • LoRaWAN and NB-IoT compatible
  • Easy installation
  • Low maintenance

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SFM-5 Sap flow sensor

The new UGT SFM-5 is one of the most advanced sap flow sensors on the market. With this sensor, you can perform minimally invasive, high-precision sap flow measurements on all trees with a trunk diameter greater than 1 cm. It is unique in that it can measure up to 33 parameters, allowing you to also determine the water content of the sapwood. You can use the SFM-5 in all climates without restrictions in the field, but also for research in the greenhouse or laboratory. Thus, the sensor offers you the greatest possible flexibility and is suitable for pure users as well as for scientific questions dealing with plant water use, physiology or hydrology.

The new version (2023), successor of the SFM-4, is even more compact and inconspicuous, as the electronics are now built into the sensor head. The needles are even more stable and now 8 instead of 6 mm apart, also the needle diameter is slightly larger with 1.6 mm instead of 1.3 mm. The temperature sensor has been reworked once again and now works even better and more consistently. The measuring algorithms remain the same.

How does the SFM-5 work?

The acquisition of the parameters is based on the heat pulse method, which has been successfully used since the 1930s. For this purpose, the sensor head is equipped with three needles, consisting of a central heating needle and two temperature measuring needles, each with a downstream and an upstream thermistor (10 and 20 mm from the needle tip). This three-probe configuration allows determination of sap flow from the root to the canopy and vice versa, with excellent detection of both high and low sap flow rates.

The plug & play capable sensor is connected to a smart interface, built on a microprocessor, which controls all operational settings and calculations, records parameters, converts analog signals into calibrated values and outputs them via the serial interface.

How does the data evaluation work?

The SFM-5 can be connected to all data logger models and brands that support the SDI-12 output protocol, but is also LoRaWAN and NB-IoT compatible. In conjunction with other SFM-5 sensors, dendrometers and environmental sensors such as water potential, soil moisture, evaporation, solar radiation, etc., you can set up customized measurement fields and operate them in a user-friendly way. Simply connect the sap flow sensor to our configured data acquisition or data transmission solutions. We are also happy to assist you in connecting the sensor to your existing data logger, IoT devices, or similar.

You can read out the raw data of all parameters and analyze them as needed (no "black box"). We are happy to provide you with a free Excel evaluation file with the SFM-5 sensors. With the help of the Excel file, the sap flow density and the sap flow, based on the data obtained from the raw temperature da

The UGT SFM-5 sensor is supplied with a sensor unit and a smart interface as well as 6 stainless steel sleeves for installing the needles into the sapwood.

The SFM-5 installation kit is recommended for mounting the sensor. It contains a special drilling template with tension belt holder, a tension belt, 10 x 1.85 mm drill bits and vacuum grease.

For storing and reading out the data, an SDI-12 capable data logger or alternatively our UGT LoRaWAN distribution box with/without UGT LoRaWAN gateway is required.

In addition, we recommend our radiation shield, which protects the entire sensor unit from solar radiation and thus reduces the susceptibility to errors in the measurement due to thermal gradients. As standard, the radiation shield is supplied in white color with holder for a tension belt and the tension belt itself. Optionally, the radiation shield can be covered with a customized camouflage foil.



Sap flow measurements

Measurement Range

-200 to >+1000 cm/hr heat velocity

Measurement Accuracy

<3 % or ±0.1 cm/hr heat velocity

Measurement Resolution

0.001 cm/hr heat velocity

Measurement Points

2: outer and inner

Measurement Theory

Dual Method Approach, Heat Ratio (Slow Rates

of Flow Method), Tmax

Stem (Sapwood) water content measurements

Measurement Range

0 to 100 % volumetric

Measurement Accuracy


Measurement Resolution


Measurement Points

2: downstream outer and inner

Stem (Sapwood) Temperature Measurements

Measurement Range

-30 to +70 °C

Measurement Accuracy

±0.015 °C

Measurement Resolution

0.001 °C

Measurement Points

4: down- and upstream outer and inner

Sensor specifications

Housing dimensions W x D X H

ca. 13 x 25 (55 mm with needles) x 55 mm

Needle dimensions

L: 30 mm; Ø1.6 mm

Position of the thermistors

outside: 10 mm; inside: 20 mm

Distance between needles

8 mm

Response Time

200 milliseconds

Power Input

12 VDC

Power Consumption

idle: 4 mA; measure: 270 mA; typical measuring cycle: 0,4 mAhr

Heating resistance (typical)

39 Ohm

Sensor Output

SDI-12 (ver. 1.4)

Measurement Duration

120 seconds

Environmental Rating

IP68; -30 to +70 °C

Enclosure Materials

Acrylonitrile Styrene Acrylate

Needle Materials

Stainless Steel (304)

Cable Materials

Ozone, UV and weather-resistant according to

EN 50396 and HD 605 S2

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