UMP-1 BT Plus Soil Moisture Sensor

The UMP-1 BT sensor is the wireless version of the UMP-1 sensors and opens up the market for smartphone based measuring technology. Measurement data are transmitted via Bluetooth directly to and stored on an Android smartphone.  The necessary app can be downloaded from the Google Play Store and installed by the user on any Android smartphone.  As an additional option, our complete package includes an outdoor-capable smartphone with preinstalled app. Up to 7 probes can be managed simultaneously using the app, and measurement data can be stored and visualized. During measurement, the data can be depicted as graph or as table of readings.

To enable an appropriate use the UMP-1 BT is available in two different versions. The UMP-1 BT is designed for surface installation in the field at different places, in particular locations that are difficult to access (short- and medium-term). The extended version is the UMP-1 BTim. It consists of a shaft with the integrated UMP-1 BT sensor, a height-adjustable handgrip, a smartphone holder and a spring guide for inserting the measuring rods. This device has all possible advantages to fast and easy carry out measuring campaigns with lots of single measurements, distributed over large areas.

The UMP-1 BT is made of plastic or stainless steel while the measuring rods (antennas) are always consist of stainless steel. The sensor has an integrated storage battery which is switched on for the measurement and then switched off again. The supply voltage is additionally recorded. Thus, the battery can be charged in time to prevent data loss.

The UMP-1 determines the soil moisture by measuring the relative permittivity (εr) of the soil. Additionally, it is possible to measure the soil Temperature (°C) and the conductivity (mS/cm). The precise conductivity measurement takes place independently of the water content measurement. In case of unusually high conductivities the sensor determines too high permittivity’s, because εr is salt depending. To correct such permittivity’s and thus the water content values the conductivity measurement can be used.

The measurement principle of measuring the water content corresponds neither to the TDR nor FDR method. The sensor operates with continuous signal at constant frequency (60 MHz). Unlike the FDR procedure the phase shifting, i.e. a time offset between the original and the reflected signal, is considered to determine the permittivity. Each time offset corresponds with an εr, defined in a range of values sorted in a look-up table. Each look-up table of all UMP-1 sensors are individually calibrated. Then by the regression function according to Topp and Davis the water content is calculated and output in % Volume. For independent water content calculations, according to other models, the εr value can be retrieved.

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  • fast and easy measurement
  • high accuracy
  • independent conductivity measurements
  • smartphone instead of a handheld device
  • wireless operation by data transfer via Bluetooth
  • compatible with all Android smartphones
  • mobile use in the field at different places, in particular locations difficult to access
  • data easily accessible and clearly presentable in the smartphone
  • storage battery only switched on for measurement -> saves energy


Measurement frequency for water content: 60 MHz
Antenna length / diameter: 100 mm / 3 mm
Water content measurement range: 0 … 100 % Vol. water content
Water content accuracy: ± 2%
Dielectric coefficient ε measurement range: 0 … 80
Electrical conductivity measurement range: 0,001 … 5mS/cm
Optional data extension to 40mS/cm possible
Electrical conductivity accuracy: ± 1%
Soil temperature measurement range: -20 … 60 °C
Soil temperature accuracy: ±0.2°C (across the entire temperature range)
Measurement volume: 1000 ml
Working temperature range: -20 … 60 °C



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