Acclima TDR-315N Sensor (SDI-12) Data Sheet

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The TDR-315N is a replacement to the former Acclima TDR-315L. It has a high voltage waveform output, which makes it effective in taking measurements when the soil electrical conductivity is high. It also consumes more power than the TDR-315H.

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Table of Contents

TDR-315N-SoilSmart Soil Moisture Sensor

Description

The TDR-315N is a replacement to the former Acclima TDR-315L. It has a high voltage waveform output, which makes it effective in taking measurements when the soil electrical conductivity is high.  It also consumes more power than the TDR-315H. 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 form factor is designed for shallower horizontal installations where it is forced 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.

Features

  • SDI-12 Interface
  • 3-element 15 cm stainless steel waveguide
  • 5 m 3-conductor waterproof cable (standard)
  • Waterproof Epoxy-filled Housing
  • 20% to 80% Incident Wave Rise Time: 300 ps
  • Waveform Digitizing Resolution: 5 ps
  • Incident Wave Amplitude:  2.3 V

Measurement Functions

  • Volumetric Water Content:                          0% to 100%
  • Medium Permittivity:                                     1 to 100
  • Medium Bulk Electrical Conductivity:       0 to 6000 µS/cm
  • 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

100

   Resolution

0.1

   Repeatability (RMS deviation)

0.07

   Accuracy

-2

+2

   Stability with Bulk Electrical Conductivity (0-3000 uS/cm)

-1

+1

    

VOLUMETRIC WATER CONTENT (VWC)

   Range[1]

0

100

%

   Resolution

0.1

%

   Repeatability (RMS deviation)

0.07

%

   Accuracy

-2

+2

%FS[2]

   Stability with Bulk Electrical Conductivity (0-3000 uS/cm)

-1

+1

%FS

    

TEMPERATURE[3]

   Range

-40

+60

°C

   Resolution

0.1

°C

   Repeatability (RMS deviation)

0.01

°C

   Accuracy (+5 to +35 °C)

-0.25

+0.25

°C

   Accuracy (-15 to +50 °C)

-0.5

+0.5

°C

    

BULK ELECTRICAL CONDUCTIVITY (BEC)

   Range

0

6000

uS/cm

   Resolution

1

uS/cm

   Repeatability (RMS deviation)

3

uS/cm

   Accuracy (0 – 1000 uS/cm)

-25

+25

uS/cm

   Accuracy (1000 – 2500 uS/cm)

-2.5

+2.5

%

   Accuracy (2500 – 6000 uS/cm)

-5

+5

%

[1] VWC is calculated based on 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 see a reading of 100%, the sensor must be fully immersed in water at 20C with at least 2 cm of water around the rods on all sides and beyond the tips of the rods. VWC readings higher than 100% are possible when the permittivity is higher than 80.

[2] Percent Full scale, or +/- 2 percentage points

[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.

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

+60

°C

-40

+140

°F

Operating Conditions

Parameter

Min

Max

Units

Operating Supply Voltage

+6.5

+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

0.3 typical

sec

   Sensor read current (Supply Voltage = 12V)

118 typical

mA

   Sensor read current (Supply Voltage = 7V)

150 typical

mA

   Sensor communications current

6 typical

mA

SDI-12 Data Line Electrical Characteristics

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

Physical Characteristics

Dimensions (without cable)

21 cm x 5.3 cm x 2 cm

Weight (without cable)

105 g

Cable weight

32.7 g/m

Composition

304 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

TDR-315N Graphic
By Scott Anderson
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