Acclima - Model True TDR-310H -Soil Water Temperature BEC Sensor with Rounded form Factor

This TDR is from the same family of the other Acclima True TDRs, however its rounded form factor allows it to easily attached to a (schedule 40) 1" PCV pipe and/or be inserted into an access tube as small as 1.25" (schedule 40 PVC) to be inserted into the soil at a specified depth.

• 3-element 10 cm stainless steel waveguide
• 34 mm round cross section with glue-on protrusion for mating with 1" schedule 40 PVC pipe
• 10 m 3-conductor waterproof cable
• Waterproof Epoxy-filled Housing
• 20% to 80% Incident Wave Rise Time: 150 ps
• Waveform Digitizing Resolution: 5 ps

• Volumetric Water Content: 0% to 100%
• Medium Permittivity: 1 to 80
• Medium Bulk Electrical Conductivity: 0 to 5000 nS/cm
• Medium Temperature: -40 to +60 degrees C
• Pore Water EC (Hilhorst Model): 0 to 55000 nS/cm

A major advantage of the TDR-310H over its predecessor TDR-310S is that its battery life has been increased 10 fold. This is due to lower current consumption and a faster read time.

• Read Time (from issuance of read command until the return of data) 0.25 seconds
• Operating Voltage Range: 3.5 to 15 volts dc
• Idle Current Consumption: < 10 µA
• Idle Daily Energy Consumption @ 3.5 v: 2 J/day

Permittivity is calculated directly from waveform propagation time and does not incorporate any voltage or current parameters. Hence the permittivity calculation is independent of soil electrical conductivity. This is the main advantage of true Time Domain Sensors over other types of sensors.

• Reading Range: 1 to 80 relative permittivity units
• Reporting Resolution: 0.1 relative permittivity units
• Repeatability (RMS deviation): 0.07 permittivity units

Reporting Accuracy:

• Coarse and medium textured soils: ±1 relative permittivity units
• Fine textured soils: ±2 relative permittivity units
• Stability of permittivity readings vs Bulk EC: < 1 relative permittivity unit 0 to 4000 µS/cm BEC

Volumetric Water Content Reporting:
VWC is calculated from permittivity using the Topp equation. Hence the accuracy of VWC reporting is that of the permittivity reporting and those further small errors imposed by the Topp equation. Note that the Topp equation is effective only to about 50% VWC. Acclima has replaced that segment of the equation with a linear function of propagation time beyond 50% VWC.

• Reading Range: 0 to 100% VWC
• Reporting Resolution: 0.1% VWC
• Repeatability (RMS deviation): 0.07%

Reporting Accuracy:

• Coarse and medium textured soils: ±1 percentage point
• Fine textured soils: ±2.5 percentage points
• Stability of VWC readings vs Bulk EC: < 1 percentage point 0 to 4000 µS/cm BEC

Bulk Electrical Conductivity Reporting:
Bulk Electrical Conductivity of the soil is calculated from soil resistance measurements between the waveguide elements. Chromium oxide deposits on the waveguide elements becomes significant at high EC levels and the error correspondingly degrades in accuracy at those levels.

• Reading Range: 0 to 5000 µS/cm
• Reporting Resolution: 1 µS/cm
• Repeatability (RMS deviation): 3 µS/cm

Reporting Accuracy:

• 0 to 1000 µS/cm 25 µS/cm
• 1000 to 2000 µS/cm ±2.5%
• 2000 to 5000 µS/cm ±5%

Temperature Reporting:
Soil Temperature is measured with a highly precise thermistor that is located about 2mm from one of the outer waveguide electrodes.

• Reading Range: -40C to +60C
• Reporting Resolution: 0.1 degree C
• Repeatability (RMS deviation): .01 % C
• Reporting Accuracy: ±0.25 degrees C

Pore Water EC Reporting:
This reading is calculated from permittivity and bulk EC using the Hilhorst model with an assumed soil type. Hence it is of limited accuracy and should be used only as a ball-park reading.