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SI-121: Research-Grade Narrow Field of View Infrared Radiometer Sensor

Updated:2025-03-13

Brand: Apogee
Model: SI-121-SS
Description: The SI-121 is an unamplified analog sensor with a voltage output and high-quality cable terminating in pre-tinned pigtail leads for easy connection to dataloggers and controllers. The sensor has a 18°
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Product Details

SI-121: Research-Grade Narrow Field of View Infrared Radiometer Sensor Functional Characteristic：

User's Manual Technical Drawing

The SI-121 is an unamplified analog sensor with a voltage output and high-quality cable terminating in pre-tinned pigtail leads for easy connection to dataloggers and controllers. The sensor has a 18° half-angle field of view and a response time of 0.6 seconds. Typical applications include plant canopy temperature measurement for use in plant water status estimation, road surface temperature measurement of determination of icing conditions, and terrestrial surface (soil, vegetation, water, snow) temperature measurement in energy balance studies. Sensor includes IP68 marine-grade stainless-steel cable connector 30 cm from head to simplify sensor removal and replacement for maintenance and recalibration. The SI-121-SS is designed to be mounted with an Apogee AM-250 commercial-grade mounting bracket.

SI-121: Research-Grade Narrow Field of View Infrared Radiometer Sensor Drawing：

SI-121 Drawing

SI-121: Research-Grade Narrow Field of View Infrared Radiometer Sensor Specification：

Approximate Sensitivity	30 μV per C
Output from Thermopile	Approximately -2.2 mV to 2.2 mV for a temperature difference from -55 to 55 C
Output from Thermistor	0 to 2500 mV (typical, depends on input voltage)
Input Voltage Requirement	2500 mV excitation (typical, other voltages can be used)
Calibration Uncertainty (0 to 50 C)	0.2 C, when target and detector temperature are within 20 C
Calibration Uncertainty (-30 to 65 C)	0.2 C, when target and detector temperature are within 20 C
Calibration Uncertainty (-40 to 80 C)	0.5 C, when target and detector temperature are different by more than 20 C
Measurement Repeatability	Less than 0.05 C
Stability (Long-term Drift)	Less than 2 % change in slope per year when germanium filter is maintained in a clean condition
Response Time	0.6 s, time for detector signal to reach 95 % following a step change
Field of View	18? half-angle
Spectral Range	8 to 14 μm; atmospheric window
Operating Environment	-50 to 80 C; 0 to 100 % relative humidity (non-condensing)
Dimensions	23 mm diameter, 60 mm length
Mass	190 g (with 5 m of lead wire)
Cable	5 m of four conductor, shielded, twisted-pair wire with TPR jacket (high water resistance, high UV stability, flexibility in cold conditions), additional cable available
Warranty	4 years against defects in materials and workmanship
Manufactured	Made in the USA