|  |

| |

Enabling better global research outcomes in soil, plant & environmental monitoring.

Digital TDT Soil Moisture

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 digitised Time Domain Transmissometry in a low-cost instrument, providing highly accurate, absolute readings of soil moisture under all conditions of temperature and soil chemistry where crops will grow. No other sensor on the market matches its accuracy and stability. Independent test data from leading soil physicists verifies this extra-ordinary claim and are available upon request.

  • Sensor requires no calibration
  • Works in all soils
  • Highly stable under a wide range of soil conductivity and temperature
  • Linear range of 0 – 100% volumetric water content
  • Made with durable inert materials
  • Very low power, battery operable
  • SDI-12 version 1.3 compliant
  • Low cost

The Digital TDT Sensor incorporates a modified SDI-12 interface capable of connecting directly to Acclima data loggers or any other third party SDI-12 (version 1.3) compliant device. Acclima’s modified SDI-12 interface is also capable of auto-detection and address collision repair.

Physical Characteristics:
Dimensions (without cable): 20cm x 5.33cm x 1.5cm
Weight (with 7.5m cable): 220g
Composition (exposed to soil): Type 304 Stainless Steel, epoxy-based potting compound
Cable Type: UV Resistant PVC sheath (insulation), 3 conductor, 22 Ga.
Environmental Characteristics:
Operating Temperature Range: 1 to 50°C
Storage Temperature Range: -20 to 75°C
Surge Protection: 6kV @ 3kA, 8/50us
Operational Characteristics
Volumetric Water Content Range: 0 to 100%
Resolution: 0.06% VWC
Absolute VWC Accuracy: ±2% (typical)
VWC Temperature Stability: ±1% of full scale 1 to 50°C
VWC Soil EC Stability: ±1% of full scale 0 to 5 dS/m bulk EC.
Temperature Reporting Accuracy: ±1°C, 0 to 70°C
Architectural Characteristics:
Technology: Waveform Digitising Time Domain Transmissometer
Effective Acquisition Bandwidth: 200 Giga-samples/sec
Propagation Time Resolution: 5 ps
Waveform Propagation Resolution: 1.5mm in air, 0.16mm in water
Waveguide Length: 30cm
Permittivity to VWC Calculation: Modified Dielectric Mixing Model
Propogated Waveform Bandwith: > 2 GHz
Communications Characteristics:
Communications Protocol: SDI-12 Revision 1.3
Maximum Cable Length: 60 meters (200 ft)
Maximum Devices per Cable: 50
Power Characteristics:
Operating Voltage Range: 4 – 15V DC
Listening/Sleep Mode Current: 15 uA (18 uA at 50°C)
Communications Current: 2.5 mA typical, 4 mA max
Read Moisture Comm Time: 425 ms total for each read cycle
Moisture Sense Current: 30 mA at 12V DC input voltage
55 mA at 6V DC input voltage
75 mA at 4V DC input voltage
Moisture Sense Time: 450 ms for each moisture sensing operation

Accepted article: Evaluation of a digital TDR for determination of permittivity and bulk electrical conductivity
Dr. Robert Shwartz | USDA Agricultural Research Service, Bushland, Texas | True TDR

Evaluation of a Direct-Coupled TDR for Determination of Soil Water Content & Bulk EC
Dr. Robert Shwartz | USDA Agricultural Research Service, Bushland, Texas | True TDR

Soil Water Sensors for Agriculture – Theory & Issues
Dr. Steve Evett | USDA Agricultural Research Service, Bushland, Texas | True TDR

Strategies to Improve Productivity in a Water Stressed Future
Dr. Steve Evett | USDA Agricultural Research Service, Bushland, Texas | True TDR


A time domain transmission sensor with TDR performance characteristics
J.M. Blonquist, S.B. Jones, B. Robinson | Utah State University | Acclima TDT

Using Soil Water Sensors to Improve Irrigation Management
J. Chavez | Colorado State University | Acclima TDT

In Soil & Down Hole Soil Water Sensors: Characteristics for Irrigation Management
R. Lascano, Dr. Steve Evett, M. Pelletier, R. Schwartz | USDA | Acclima TDT

Performance Evaluation of  Selected Soil Moisture Sensors
J. Chavez, J. Varble, A. Andales | Colorado State University | Acclima TDT