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Enabling better global research outcomes in soil, plant & environmental monitoring.

SO-411: SDI-12 Soil Oxygen Sensor

The SO-411 Soil Response Thermistor Reference Oxygen Sensor has a standard response time of 60 seconds and is designed for use in soil applications. It comes with a thermistor temperature sensor to correct for temperature changes and a restive heater to raise the temperature of the membrane approximately two degrees above ambient temperature to keep condensation from occurring on the Teflon membrane and blocking the diffusion path of the sensor.

Typical applications include measurement of O2 in laboratory experiments, monitoring gaseous O2 in indoor environments for climate control, monitoring of O2 levels in compost piles and mine sailings, monitoring redox potential in soils, and determination of respiration rates through measurement of O2 consumption in sealed chambers or measurement of O2 gradients in soil/porous media.

Input Voltage Requirement 4.5 to 24 V DC
Current Drain 0.6 mA (quiescent), 1.3 mA (active)
Measurement Range 0 to 100% O2
Measurement Repeatability Less than 1% of mV output at 20.95% O2
Non-linearity Less than 1%
Long-term Drift (Non-stability) 1.0 mV per year
Oxygen Consumption Rate 2.2 µmol O2 per day at 20.95% O2 and 23°C
Response Time 60 seconds
Operating Environment -20 to 60°C, 0 to 100% relative humidity (non-condensing), 60 to 140 kPa
Input Voltage Requirement 12 V DC continuous (for heater); 2.5 V DC excitation (for thermistor)
Heater Current Drain 6.2 mA (74 mW power requirement when powered with 12 V DC source)
Thermistor Current Drain 0.1 mA DC at 70°C (maximum, assuming input excitation of 2.5 V)
Dimensions 32 mm diameter, 69 mm length
Mass 175 g (with 5 m lead wire)
Warranty 4 years against defects in materials and workmanship

Heated Detector
The protective membrane in front of the oxygen sensor can be heated to prevent water from condensing on the membrane and blocking the diffusion path. The heater is typically used when sensors are deployed in soil or compost where relative humidity is close to 100%.

Rugged Housing
Housed in a polypropylene body and electronics are fully potted, ideal for long-term deployment in porous media, including acidic environments (mine tailings). Two head options are available: a diffusion head that creates a small air pocket for measurement in porous media and a flow-through head with two adapters for tubing that allows measurement of gas flowing in lines.

Internal Temperature Sensor
All oxygen sensors have an internal thermistor (type-K thermocouple is available upon request) that allows for temperature monitoring and correction of signal for temperature effects.

Simple Calibration
Voltage output is linearly proportional to absolute amount of oxygen. Calibration is accomplished by measuring the voltage under ambient conditions (atmosphere is 20.95% O2) and deriving a linear calibration factor (slope). A zero offset can be measured with N2 gas (recommended for measurements below 10% O2).

Typical Applications
Applications include: measurement of O2 in laboratory experiments, monitoring gaseous O2 in indoor environments for climate control, monitoring of O2 levels in compost piles and mine tailings, monitoring redox potential in soils, and determination of respiration rates through measurement of O2 consumption in sealed chambers or measurement of O2 gradients in soil/porous media.