The SO-110 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.
Measurement Range 0 to 100 % O₂
Sensitivity (at sea level, 101.3 kPa) 52-58 mV in 21 % O₂, 2.6 mV per % O₂, 26 µV per 0.01 % O₂
Output at 0 % O2 5 % of output at 20.95 % O₂ or 2.5 ± 1 mV
Response Time (time required to read 90 % of saturated response) 60 s
Measurement Repeatability Less than 0.1 % of mV output at 20.95 % O₂
Non-linearity Less than 1 %
Signal Decrease per Year 1 mV per year
Oxygen Consumption Rate 2.2 µmol O₂ per day at 20.95 % O₂ and 23 C
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 DC)
Dimensions 32 mm diameter, 68 mm length
Mass 175 g (with 5 m of lead wire)
Cable 5 m of six conductor, shielded, twisted-pair wire
Warranty 4 years against defects in materials and workmanship
Dr. Wendy Yang’s Global Change Ecology Lab, at the University of Illinois at Urbana-Champaign, is currently using the Apogee SO-110 oxygen sensor, with the optional diffusion head, for quasi-continuous measurements of bulk soil oxygen concentration in managed and natural ecosystems. Their quasi-continuous field measurements of soil oxygen has allowed them to correlate soil oxygen concentrations with process rates and determine how soil oxygen concentrations relate to precipitation and soil temperature, which can drive high biological oxygen demand to induce anoxia. The Apogee SO-110 allows Dr. Wendy Yang’s Global Change Ecology Lab to collect long-term data sets in the field without fear of compromising the sensors under harsh conditions, due to the sensors ability to withstand cold winter temperatures and wet conditions.
Oxygen is a major control for reduction-oxidation reactions in soil and can lead to the production or consumption of methane and nitrous oxide, both potent greenhouse gases. Processes such as methanogens and nitrous oxide reduction to dinitrogen were once thought to be restricted to flooded or saturated soils such as those found in wetlands, however, Dr. Wendy Yang’s lab has documented the importance of these processes in unsaturated soils from upland ecosystems. Their measurements have allowed them to correlate soil oxygen concentration with process rates and determine how soil oxygen concentrations relate to precipitation and soil temperate, even under saturated soil conditions. They are currently investigating these relationships in agricultural fields in the Midwest to better understand how current land management and historical soil drainage patterns mediate soil greenhouse gas emissions.