The SMT-100 combines the advantages of the low-cost FDR sensor system with the accuracy of a TDR system. Like a TDR, it measures the travel time of a signal to determine the relative permittivity εr of the soil. And like a FDR, it converts εr into an easy to measure frequency. The SMT-100 utilizes a ring oscillator to transform the signal’s travel time into a frequency. The resulting frequency (>100 MHz) is high enough to operate well even in clayey soils.

Compact, functional and robust: the PCB board based design allows for an economic design, and the blade shape facilitates installation. The casing and cable are water sealed. The SMT-100 is connected to a logger or handheld for data management. Different communication protocols are available (RS485 or SDI-12), as well as analogue output. It is bus capable and thus, multiple sensors can be connected to one logger.

The SMT-100 determines the volumetric water content and the soil temperature. It has a broad measurement range, it is maintenance free and frost resistant. With a short response time and low disturbance by salinity it is designed for a long-term observation. Additionally, it is possible to retrieve the relative Permittivity.



  • Frost resistant
  • Reliable measurement
  • Maintenance free
  • Long lifetime
  • Fast response
  • Low influence of salinity and pH
  • Cost efficient

Technical Specifications

Signal output - digital (RS485 with UGT-protocol. SDI-12 is available on request)
- analog (0-1V, other voltage ranges on request)

Cable length

Power supply


10 m

digital 4 ... 24 VDC (analog 12 ... 24 VDC)

182 x 30 x 12 mm


Measurement range


0-60 % vol (0 ... 100 % vol with limited accuracy)

Accuracy with generic calibration

±3 % vol in mineral soils with average salinity over 0 ... 50 % vol

Accuracy after  specific calibration

±1 % vol


0.1 % vol




-40 ... +80 °C (analog -40 ... +60 °C)

extended temperature range on request


±0.2 °C (analog ±0.8 °C)


0.01 °C (analog 0.2 °C)



Ordering Details:

Art.-Nr.:  118600               SMT-100


Tel.: +49 (0) 33432 - 89 575
Fax: +49 (0) 33432 - 89 573

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Tel.: +49 (0) 8161 - 23 46 441
Fax: +49 (0) 8161 - 23 46 443