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

SO Apogee Oxygen Sensors

Apogee oxygen sensors are designed to measure 0 - 100% oxygen and come with tinned leads to connect to a data logger. The SO Series Oxygen Sensors are designed for use in the field or in the lab. All Apogee sensors have an embedded thermistor or thermocouple for temperature corrections.

The AO-001 Diffusion Head is used for field or soil measurements of oxygen concentration. The AO-002 Flow Through Head is used for laboratory applications.

Apogee Instruments has 4 types of oxygen sensors:

SO-110: the most popular sensor; ideal for soils and field applications; thermistor temperature corrections.

SO-120: soils and field applications; thermocouple temperature corrections.

SO-210: fast response but shorter life-span; ideal for laboratory applications; thermistor temperature corrections.

SO-220: fast response but shorter life-span; ideal for laboratory applications; thermocouple temperature corrections.

Measurement Range: 0 to 100% O2
Sensitivity: 2.6 and 0.6 mV per % O2 for SO-100 and SO-200 series, respectively
Output at 0% O2: 6% and 3% of output at 20.95% O2 for SO-100 and SO-200 series, respectively
Measurement Repeatability: < 0.1% of mV output at 20.95% O2
Non-linearity: < 1%
Non-stability (Signal Decrease): 1 and 0.8 mV per year for SO-100 and SO-200 series, respectively
Oxygen Consumption Rate: 2.2 µmol O2 per day at 20.95% O2 and 23°C
Response Time: 60 and 14s for SO-100 and SO-200 series, respectively
Operating Environment: -20 to 60°C, 0 to 100% relative humidity (non-condensing), 60 to 140 kPa
Input Voltage Requirement: 12V DC continuous (for heater); 2.5V DC excitation (for thermistor)
Heater Current Drain: 6.2 mA
Thermistor Current Drain: 0.1 mA DC at 70°C (maximum, assuming input excitation of 2.5V DC)
Dimensions: 3.2 cm diameter, 6.8 cm length
Mass: 175g (with 5m of lead wire)
Cable: 5 m of six conductor, shielded, twisted-pair wire

Oxygen (O2) is the second most abundant gas in the atmosphere and is essential to life on Earth. Absolute oxygen concentration determines the rate of many biological and chemical processes. Oxygen is required for aerobic respiration. In addition to measurements of absolute oxygen concentration, relative oxygen concentration is also often measured and reported.

Oxygen sensors are used to measure gaseous or dissolved oxygen. There are multiple different techniques for measuring gaseous oxygen. Three of the more widely used sensors for environmental applications are galvanic cell sensors, polarographic sensors, and optical sensors. Galvanic cell and polarographic sensors operate similarly, by electrochemical reaction of oxygen with an electrolyte to produce an electrical current. The electrochemical reaction consumes a small amount of oxygen. Unlike polarographic oxygen sensors, galvanic cell sensors are self-powered and do not require input power for operation. Optical oxygen sensors use fibre optics and a fluorescence method to measure oxygen via spectrometry.

Typical applications of Apogee oxygen sensors include measurement of oxygen in laboratory experiments, monitoring gaseous oxygen in indoor environments for climate control, monitoring of oxygen levels in compost piles and mine tailings, and determination of respiration rates through measurement of oxygen consumption in sealed chambers or measurement of oxygen gradients in soil/porous media.
Apogee Instruments SO-100 and SO-200 series oxygen sensors consist of a galvanic cell sensing element (electrochemical cell), Teflon membrane, reference temperature sensor (thermistor or thermocouple), heater (located behind the Teflon membrane), and signal processing circuitry mounted in a stainless steel housing (or ABS plastic housing for use in acidic environments), and lead wires to connect the sensor to a measurement device. Sensors are designed for continuous gaseous oxygen measurement in ambient air, soil/porous media, sealed chambers, and in-line tubing (flow through applications). SO-100 and SO-200 series oxygen sensors output an analogue voltage that is directly proportional to gaseous oxygen.