Acclima Digital True TDR-305N Sensor (SDI-12) Data Sheet

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The TDR-305N is a modified version of the TDR-310N. The very short waveguide allows this sensor to make very shallow measurements and to be used in higher conductivity environments with a sacrifice in total measurement volume.

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Table of Contents

Description

The TDR-305N is a modified version of the TDR-310N.  The very short waveguide allows this sensor to make very shallow measurements and to be used in higher conductivity environments with a sacrifice in total measurement volume.  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 easy vertical installation in an augured hole using a 34 mm flat-bottomed auger. It mates with a 1” schedule 40 PVC pipe that acts as a handle in its installation to any desired depth. 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 5 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 10000 µS/cm
  • Medium Temperature:                                  -40 to +55 degrees C
  • Pore Water EC (Hilhorst Model):              0 to 55000 µS/cm

Measurement Performance

ParameterMinMaxUnits
RELATIVE PERMITTIVITY
   Range1100
   Resolution0.1
   Repeatability (RMS deviation)0.07
   Accuracy-2+2
   Stability with Bulk Electrical Conductivity (0-6000 uS/cm)-1+1
    
VOLUMETRIC WATER CONTENT (VWC)
   Range[1]0100%
   Resolution0.1%
   Repeatability (RMS deviation)0.07%
   Accuracy-2+2%FS[2]
   Stability with Bulk Electrical Conductivity (0-6000 uS/cm)-1+1%FS
    
TEMPERATURE[3]
   Range-40+60°C
   Resolution0.1°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)
   Range010000uS/cm
   Resolution1uS/cm
   Repeatability (RMS deviation)3uS/cm
   Accuracy (0 – 1000 uS/cm)-25+25uS/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.

ParameterMinMaxUnits
Supply Voltage (Measured between the red and white wires)-16+16Volts
SDI-12 Data Voltage (Blue-White wires)-16+16Volts
External Voltage Applied to sensor rod-0.3+4Volts
Electrostatic discharge, center rodIEC 61000−4−2 (ESD) 
Storage Temperature-40+60°C
-40+140°F

Operating Conditions

ParameterMinMaxUnits
Operating Supply Voltage+6.5+15Volts
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)< 10uA
   Idle Current (-35 to +50 °C)< 50uA
   Sensor read time0.3 typicalsec
   Sensor read current (Supply Voltage = 12V)118 typicalmA
   Sensor read current (Supply Voltage = 7V)150 typicalmA
   Sensor communications current6 typicalmA

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)15 cm x 3.3 cm
Weight (without cable)121 g
Cable weight32.7 g/m
Composition304 Stainless Steel, Epoxy, ABS Plastic
Cable3 copper conductor, 22 Ga., waterproof and UV resistant PVC jacket, 4.8mm overall diameter
Communication ProtocolSDI-12 Version 1.4
By Scott Anderson
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