TDR-315H Data Sheet – Acclima ME

Acclima Digital True TDR-315H Soil Moisture Sensor (SDI-12) Data Sheet

September 4, 2022

The TDR-315H soil moisture sensor is the replacement to the former Acclima TDR-315 and TDR-315L soil water content sensors. It is fully compatible with those sensors but incorporates several improvements.

Description

The TDR-315H is one of Acclima’s H-series sensors, which are very low power and suited perfectly for power-conscious applications. Being part of the Soil Smart Series means that its advanced waveform analysis works with all mineral soil types. It is a complete integrated time domain reflectometer that combines ultra-fast waveform generating and digitizing functions with a precision 5 pico-second resolution time base and highly sophisticated waveform digitizing and analyzing firmware that provides true time domain analysis of soil-propagated waveforms. Its longer waveguides provide a very large sampling volume and high accuracy of the waveform propagation.

Its form factor is designed for shallower horizontal installations where it is pushed into the sidewall of a trench that has been dug to the desired measurement depth. A probe guide is provided to ensure that the waveguide rods are parallel when pushing them into the soil. It provides reading data through a 3-wire SDI-12 interface and is compatible with any data recorder that is compliant with SDI-12 version 1.4 and earlier.

Its longer waveguides provide a very large sampling volume and high accuracy of the waveform propagation.

Features

Ultra-low power consumption and fast response time
Designed for easy use in shallower horizontal applications
Very large sampling volume with the wide spacing and the longer 15cm waveguides
High accuracy Acclima sensor configuration
Soil Smart analysis works with all mineral soil types
Incident Wave Amplitude: 400mV
20% to 80% Incident Wave Rise Time: 150 ps
Waveform Digitizing Resolution: 5 ps
SDI-12 Interface
3-element 15 cm stainless steel waveguide
5m or 10m 3-conductor waterproof cable (standard)
Waterproof Epoxy-filled Housing

Measurement Functions

Volumetric Water Content: 0% to 100%
Medium Permittivity: 1 to 85
Medium Bulk Electrical Conductivity: 0 to 2000 µS/cm (Ɵ, ɛ repeatability degrades above 2000 µS/cm BEC)
Medium Temperature: -40 to +55 degrees C
Pore Water EC (Hilhorst Model): 0 to 55000 µS/cm

Measurement Performance

Parameter	Min	Max	Units
RELATIVE PERMITTIVITY
Range	1	85	–
Resolution	0.1		–
Repeatability (RMS deviation)	0.07		–
Accuracy	-2	+2	%FS[1]
Stability with Bulk Electrical Conductivity (0-2000 uS/cm)	-1	+1	%FS

VOLUMETRIC WATER CONTENT (VWC)
Range[2]	0	100	%
Resolution	0.1		%
Repeatability (RMS deviation)	0.07		%
Accuracy	-2	+2	%FS
Stability with Bulk Electrical Conductivity (0-3000 uS/cm)	-1	+1	%FS

TEMPERATURE[3]
Range	-40	+55	°C
Resolution	0.1		°C
Repeatability (RMS deviation)	0.01		°C
Accuracy (+5 to +35 °C)	-0.25	+0.25	°C
Accuracy (-15 to +55 °C)	-0.5	+0.5	°C

BULK ELECTRICAL CONDUCTIVITY (BEC)
Range	0	2000	uS/cm
Resolution	1		uS/cm
Repeatability (RMS deviation)	3		uS/cm
Accuracy (0 – 1000 uS/cm)	-25	+25	uS/cm
Accuracy (1000 – 2000 uS/cm)	-2.5	+2.5	%

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

[2] VWC is calculated based on relative permittivity using the formula derived by Topp with minor modifications toallow readings in slurries and pure water. The relative permittivity of water varies with temperature, so to see a reading near 100%, the sensor must be fully immersed in water long enough to equilibrate temperature with the water. The water should be at 20.5C with at least 4cm of water around the rods on all sides, beyond the tips of the
rods, and at least 1cm of the sensor body immersed. VWC readings higher than 100% are possible when the permittivity is higher than 80.

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

Absolute Maximum Ratings

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

Operating Conditions

Parameter	Min	Max	Units
Operating Supply Voltage	+3.5	+15	Volts
Operating Temperature (VWC errors due to ice)	-30	+55	°C
Operating Temperature (VWC accurate, no ice allowed)	0	+55	°C

POWER CONSUMPTION
Idle Current (sensor powered but inactive, 20 °C)	< 10		uA
Idle Current (-35 to +50 °C)	< 50		uA
Sensor read time	0.25 typical		sec
Sensor read current (Supply Voltage = 12V)	36 typical		mA
Sensor read current (Supply Voltage = 7V)	88 typical		mA
Sensor communications current	6 typical		mA

Parameter	Min	Max	Units
Supply Voltage (Measured between the red and white wires)	-16	+16	Volts
SDI-12 Data Voltage (Blue-White wires)	-16	+16	Volts
External Voltage Applied to sensor rod	-0.3	+4	Volts
Electrostatic discharge, center rod	IEC 61000−4−2 (ESD)
Storage Temperature	-40	+55	°C
Storage Temperature	-40	+140	°F

Parameter	Min	Max	Units
INPUT (when sensor is idle or receiving data)
Resistance to GND	160k	175k	Ohms
VIL (required input voltage in “marking” state)	-1	1.3	V
VIH (required input voltage in “spacing” state)	3.2	6	V

OUTPUT (when sensor is transmitting data)
Output impedance	1000	1250	Ohms
VOL (output voltage in “marking” state)	0	0.25	V
VOH (output voltage in “spacing” state)	4.7	5.2	V

Dimensions (without cable)	21 cm x 5.3 cm x 2 cm
Weight (without cable)	105 g
Cable weight	32.7 g/m
Composition	316 Stainless Steel, Epoxy, ABS Plastic
Cable	3 copper conductor, 22 Ga., waterproof and UV resistant PVC jacket, 4.8mm overall diameter
Communication Protocol	SDI-12 Version 1.4

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