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SO-421 SDI-12: Fast Response Thermistor Reference Oxygen Sensor

Updated:2025-03-13

Brand:APOGEE
Model: SO-421
Description: The SO-421 has a fast response time of 14 seconds, is designed for use in lab applications, and has high-quality cable terminating in pre-tinned pigtail leads for easy connection to dataloggers and
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Product Details

SO-421 SDI-12: Fast Response Thermistor Reference Oxygen Sensor Introduction：

user's manual

The SO-421 has a fast response time of 14 seconds, is designed for use in lab applications, and has high-quality cable terminating in pre-tinned pigtail leads for easy connection to dataloggers and controllers. It comes with a thermistor temperature sensor to correct for temperature changes and a resistive 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.

SO-421 Technical Drawing：

SO-421 Specifications:

Input Voltage Requirement	5.5 to 24 V DC
Current Drain	0.6 mA (quiescent); 1.3 mA (active)
Measurement Range	0 to 100 % O?
Measurement Repeatability	Less than 0.1 % of mV output at 20.95 % O?
Non-linearity	Less than 1 %
Long-term Drift (Non-stability)	0.8 mV per year
Oxygen Consumption Rate	0.1 μmol O? per day at 20.95 % O? and 23 C
Response Time	14 s
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)
Warranty	4 years against defects in materials and workmanship
Manufactured	Made in the USA