TDT Soil Moisture Sensor (SDI-12)

TDT Soil Water Content Sensor (SDI-12)

Product Summary

$322 – $331

Used worldwide, this TDT soil water content sensor (a.k.a., soil moisture sensor, probe, or meter) accurately measures VWC, Bulk EC, and temperature. Temperature accuracy is within 0.5˚C.

The Acclima Digital TDT® soil moisture sensor represents a revolutionary advance in the irrigation industry. It is the first soil moisture sensor to incorporate the accuracy of digitized Time Domain Transmissometry (TDT) in a low-cost instrument providing highly accurate absolute readings of soil moisture under all conditions of temperature and soil chemistry that crops will grow. No other TDT soil water content sensor on the market matches its accuracy and stability. Independent test data from leading soil physicists verify these claims and are available upon request.

This Digital TDT sensor incorporates a modified SDI interface capable of connecting directly to Acclima data loggers or any other third-party SDI version 1.4 compliant device. The Acclima modified SDI interface is also capable of auto-detection and addressing collision repair with Acclima data loggers.

Key Features

  • Works in all soils
  • Highly stable under a wide range of soil conductivity and temperature
  • Range of 0 -100% volumetric water content
  • Made with durable inert materials
  • Very low-power, battery operable
  • SDI-12 version 1.4 compliant
  • Low cost



  • Dimensions (without cable): 20 cm x 5.33 cm x 1.5 cm
  • Weight (with 5m cable): 299 grams
  • Composition: Type 304 stainless steel, crystalline-epoxy
  • PVC (insulation) cable: 3 conductor, 22 ga PVC sheath, 5


  • Operating temp range: 1 ̊C to 50 ̊C for VWC (no ice), -20
  • ̊C to 50 ̊C for the other data
  • Storage temp range: 20 ̊C to 75 ̊C
  • Lightning and surge protection: 6 kV @ 3 kA, 8/50 µs


  • Volumetric water content: 0 to 100%
  • Resolution: 0.06% VWC
  • Absolute VWC accuracy: ±2% typical
  • VWC soil EC stability: ±1% of full scale 0 to 5 dS/m BEC
  • Temp reporting accuracy: ±2 ̊C from +1 ̊C to +50 ̊C
  • EC reporting accuracy: ±0.2 dS/m 0 to 5 dS/m BEC


  • Technology: Waveform digitizing time domain transmissometer
  • Effective acquisition bandwidth: 200 giga-sample/second
  • Propagation time resolution: picosecond
  • Waveform propagation resolution: 1.5 mm in air, 0.16 mm in water
  • Waveguide length: 30 cm
  • Permittivity to VWC calculation: Modified dielectric mixing model
  • Propagation waveform bandwidth: >2 GHz


  • Communication protocol: SDI-12 Revision 1.4
  • Maximum cable length: 60 meters


  • Operating Voltage Range: 6–15 VDC
  • Listening/Sleep Mode Current: 60 µA at 50 ̊C
  • Communications Current: 6 mA typical, 8 mA max
  • Read Moisture Comm Time: 425 ms total for each read cycle
  • Moisture Sense Current: 84 mA at 12VDC input, 98 mA at 8 VDC input, 110 mA at 6 VDC input
  • Moisture Sense Time: 450 ms each sensing operation


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