SMT100
The SMT100 combines the advantages of an inexpensive FDR sensor with the accuracy of a TDR measurement. As with a TDR, the dielectric constant of the soil is determined from the signal propagation time and, as with FDR, this is converted into an easily measurable frequency. In contrast to FDR, a capacitance is not simply determined, but the propagation time is converted into a frequency using a ring oscillator. The resulting frequency (>100 MHz) is high enough to allow good measurements even in clayey soils.
Compact, functional and robust: The glass fiber reinforced board enables a cost-effective design and easy installation thanks to the blade shape. The housing and cable are waterproof. Various communication protocols are available as well as a version with analog output.
The SMT has a large measuring range. It is maintenance-free and frost-resistant. With its short measuring time and low influence from salinity, it is suitable for continuous use.
Technical data:
| measurement accuracy | Volumetric water content (VW): With factory calibration up to ± 3% (VW) in mineral soils with medium salinity of 0 to 50% VW With soil-specific calibration up to ± 1% (VW) Temperature: Typically ± 0.2°C, max. ± 0.4°C over the entire measuring range Analog version ± 0.8°C Additional measured values (digital version only): raw data Dielectric permittivity |
| resolution | 0.1% in volumetric water content or better 0.01°C or better (analog version 0.2°C) |
| measuring range | 0 to 60% volumetric water content (up to 100% volumetric water content with limited accuracy Temperature: -40 to +80°C (analog version -40 to +60°C) |
| interface variants | RS485 with TBUS RS485 with Modbus RS485 with ASCII SDI-12 Analog: 0 - 10 V (other voltage ranges on request) |
| power supply | 4-24 V DC, up to 40 mA during measurement (Analog version 12 - 24 V DC for 0 - 10 V output signal) Measurement time digital versions: less than 50 ms Measurement time analog versions: less than 200 ms |
| cable length | 10 m |
| Dimensions | approx. 18.2 cm x 3 cm x 1.2 cm |
| compatibility with data loggers | Any data logger with suitable power supply and RS485 interface (TBUS, Modbus, ASCII), SDI-12 or analog input Free PC logger software on request |
