Measure the Whole Range!

UGT SFM-4 Sensor

For measuring sap flow and determining the water content of the sapwood

The UGT SFM-4 is one of the most advanced sap flow sensors on the market. With this sensor, you can cost-effectively perform high-precision sap flow measurements on all trees with a trunk diameter greater than 1 cm. It is unique that it can measure up to 33 parameters, allowing you to determine the water content of the sapwood as well. It can be used in the field in all climates without restrictions, but can also be used for research in the greenhouse or laboratory. Thus, the UGT SFM-4 sensor offers the greatest possible flexibility and is suitable for pure users as well as for scientific questions dealing with plant water utilization, physiology or hydrology.

The acquisition of the parameters is based on the heat pulse method, which has been used successfully 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 the 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.

The UGT SFM-4 sensor 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-4 sensors, dendrometers, and environmental sensors such as water potential, soil moisture, evaporation, solar radiation, etc., customized measurement fields can be set up and operated in a user-friendly manner. Simply connect the UGT SFM-4 Sap Flow Sensor to our configured data acquisition or data transmission solutions. We are also happy to support you in connecting the SFM-4 sensor to your existing data logger, IoT devices, or similar.

The raw data of all parameters can be read out by the user and analyzed as required (no "black box"). We are happy to provide you with a free Excel evaluation file with the SFM-4 sensors. The Excel file can be used to calculate the sap flow density and the sap flow based on the thermal velocity resulting from the raw temperature data. The basis for this calculation are known and published calculation methods (HRM, Tmax, DMA).



  • Cost-effective high-precision sap flow measurements even on thin logs
  • Captures both high and low sap flow rates
  • water content of sapwood can be easily determined
  • SDI-12 output protocol is supported by a wide range of data loggers
  • LoRaWAN and NB-IoT compatible
  • Easy to install, low maintenance during operation
  • rugged design for long-term measurements
  • Output of 33 different parameters possible per measurement
  • Different methods for evaluation of the sap flow applicable (HRM, Tmax, DMA)
  • Output of raw temperature values for use in own models
  • If desired, output of calibrated sap flow value only
  • free evaluation tools in Excel for fast data analysis and interpretation


Scope of delivery as well as necessary and optional accessories:

The UGT SFM-4 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-4 installation kit is recommended for mounting the sensor. It contains a special drilling template with tension belt holder, a tension belt, 10 x 1.58 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.

Technical Data



Measuring principle

Heat Pulse Velocity (HRM) / Tmax / Dual Method Approach (DMA)

Measurement range

-200 +1000 cm/h (thermal velocity)


±0.01 cm/h (thermal velocity)


0.001 cm/h (thermal velocity)

Needle Dimension

30 x 1.3 mm

Position of Thermistors

Outer: 10 mm; Inner: 20 mm

Distance between Needles

6 mm

Epoxy Body Dimension

40 x 16 mm

Needle material

316 stainless steel

Temperature range

-30 to +70 °C

Response time

200 Milliseconds

Heater resistance

39 Ohms (typical)

Power input

12 V DC

Power consumption in idle mode

Idle mode: 4 mA; Measurement: 270 mA; Typical Measurement Cycle: 0.4 mAh

Sensor output

SDI-12 (Ver. 1.4)

Cable length

5 m (Standard) / 60 m (maximum)


1 year


Ordering Details:

Art.-Nr.:  1700600UGT SFM-4 Sensor for measuring sap flow and determining the water content of the sapwood

Principal Office Müncheberg

Umwelt-Geräte-Technik GmbH
Eberswalder Str. 58
15374 Müncheberg
Tel.: +49 (0) 33432 7559-0

Branch South

Umwelt-Geräte-Technik GmbH
Munich Airport Business Park
Lindberghstr. 7a
85399 Hallbergmoos
Tel.: +49 (0) 811 124478-0