Brand: Growlink

Acclima TDR-305W Soil Moisture Sensor (SDI-12)

The TDR-305W is a fully integrated soil water content TDR sensor (also known as a soil moisture sensor, probe, or meter) that produces accurate readings. It can be used in environments with significantly higher conductivity and challenging soil conditions. It is tuned for non-mineral soils often used in controlled environments, such as rock wool and coconut fiber, but still performs well in traditional mineral soils.

Description

The TDR-305W is a 5 cm waveguide version of the Acclima TDR-310W (10 cm). The shorter waveguide allows this sensor to be used in environments with significantly higher conductivity. Like the 310W, the SoilSmart analysis engine is also tuned for non-mineral soils commonly used in Controlled Environments, such as rock wool and coco coir, but still works well in traditional mineral soils. It also has a much higher amplitude waveform than the H-series sensors, which consumes more power but makes it very effective at taking measurements in challenging soil environments.

It is a complete integrated time domain reflectometer that combines ultra-fast waveform generation and digitization functions with a 5 picosecond precision resolution time base and highly sophisticated waveform digitization and analysis firmware that provides real-time domain analysis of ground-propagating waveforms.

Its form factor was designed primarily for ease of use in non-mineral media commonly used in vertical farming applications. A probe guide is provided to ensure the waveguide rods are parallel when driven into the soil. It provides data readout via a 3-wire SDI-12 interface and is compatible with any data recorder compatible with SDI-12 version 1.4 and earlier.

It has a much higher amplitude waveform than the H-series sensors, which consumes more power but makes it very effective at taking measurements in challenging ground environments.

Features

• Designed for easy use with rockwool blocks and even very small growing media
• Good sampling volume with wide 5 cm waveguide spacing
• Intelligent soil analysis optimized for non-mineral soil types, but still works well on mineral soils
• Ideal for high conductivity environments
• Incident wave amplitude: 2.3 V
• Incident wave rise time from 20 to 80%: 300 ps
• Waveform digitization resolution: 5 ps
• SDI-12 Interface
• 3-element, 5cm stainless steel waveguide
• 5m or 10m 3-core waterproof cable (standard)
• Waterproof epoxy filled housing

Measurement functions

• Volumetric water content: 0 to 100%
• Average Permittivity: 1 to 85
• Average electrical conductivity: 0 to 9,000 µS/cm
• Average temperature: -40 to +55 °C
• Pore Water EC (Hilhorst Model): 0 to 55000 µS/cm

Measurement performance

RELATIVE PERMITTIVITY

•     Range 1 to 100
•     Resolution 0.1
•     Repeatability (RMS deviation) 0.21
•     Accuracy ±4% FS [1]
•     Stability with bulk electrical conductivity (0-4500 uS/cm) ±1

 
VOLUMETRIC WATER CONTENT (VWC)

•     Range 0 to 100% [2]
•     Resolution 0.1%
•     Repeatability (RMS deviation) 0.5%
•     Accuracy ±5%FS
•     Stability with bulk electrical conductivity (0-9000 uS/cm) ±1%FS

 
TEMPERATURE [3]

•     Range -40 to +55 °C
•     Resolution 0.1°C
•     Repeatability (RMS deviation) 0.01 °C
•     Accuracy (+5 to +35°C) ±0.25°C
•     Accuracy (-15 to +50°C) ±0.5°C

 
BULK ELECTRICAL CONDUCTIVITY (BEC)

•     Range 0 to 9000 uS/cm
•     Resolution 1 uS/cm
•     Repeatability (RMS deviation) 3 uS/cm
•     Accuracy (0 – 1000 uS/cm) ±25 uS/cm
•     Accuracy (1000 – 2500 uS/cm) ±2.5%
•     Accuracy (2,500 – 6,000 uS/cm) ±5%
•     Accuracy (6,000 – 9,000 uS/cm) ±7.5%

[1] Full scale percentage, i.e. +/- 2 percentage points.

[2] VWC is calculated from relative permittivity using the formula derived by Topp with minor modifications to allow readings in slurries and pure water. The relative permittivity of water varies with temperature, so to obtain a reading close to 100%, the sensor must be fully immersed in the water for long enough to equilibrate to the water temperature. The water must be at 20.5°C (68°F) with at least 4 cm of water surrounding the rods on all sides beyond the rod tips, and at least 1 cm of the immersed sensor body. VWC readings greater than 100% are possible when the permittivity is greater than 80.

[3] The temperature sensing element is located near one of the outer electrodes of the waveguide.

Absolute Maximum Ratings

Voltages beyond those specified below may cause permanent damage to the sensor. These are stress ratings only, and operation at these levels is not implied.

• Supply voltage (measured between red and white wires) -16 to +16 Volts
• SDI-12 Data Voltage (Blue-White Wires) -16 to +16 Volts
• External voltage applied to the sensor rod -0.3 to +4 Volts
• Electrostatic discharge, center rod: IEC 61000−4−2 (ESD)
• Storage temperature -40 +60 °C

Operating conditions

• Operating supply voltage: 4.2 to 15 Volts
• Operating temperature (VWC errors due to ice) -30 to +55 °C
• Operating temperature (VWC accuracy, no ice allowed) 0 to +55 °C

 
ENERGY CONSUMPTION

•     Idle current (sensor powered but inactive, 20°C) < 26 uA
•     Idle current (-35 to +50 °C) < 60 uA
•     Sensor reading time 0.8 seconds (typical)
•     Sensor reading current (supply voltage = 12V) 90 mA (typical)
•     Sensor reading current (supply voltage = 7 V) 150 mA (typical)
•     Sensor communication current 3 mA (typical)

Electrical characteristics of the SDI-12 data line

INPUT (when the sensor is idle or receiving data)

•     Ground Resistance 160k to 175k Ohms
•     VIL (required input voltage in “marking” state) -1 to 1.3 V
•     VIH (required input voltage in “spacing” state) 3.2 to 6 V

 
OUTPUT (when the sensor is transmitting data)

•     Output impedance 1000 to 1250 Ohms
•     VOL (output voltage in “marking” state) 0 to 0.25 V
•     VOH (output voltage on “spacing” state) 4.7 to 5.2 V

Physical characteristics

• Dimensions (without cable): 16 cm x 5.3 cm x 2 cm
• Weight (without cable): 94 g
• Cable weight: 32.7 g/m
• Composition: 316 Stainless Steel, Epoxy, ABS Plastic
• Cable: 3 copper conductors, 22 Ga., waterproof and UV resistant PVC jacket, 4.8 mm overall diameter
• Communication Protocol: SDI-12 Version 1.4