SI-121-SS Narrow Field of View Infrared Radiometer Sensor


Apogee Instruments


The SI-121 is an unamplified analog sensor with a voltage output.
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.

915,00 €

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The Sensor measures: Temperature of a surface
Cable Length: 5 meters
Sensor for use in: Outdoor
Sensors Accessories: Mounting Shelf

The SI-121 and 18º FOV (Field Of View) sensor provides accurate measurement of the leaf-to air temperature gradient is important for irrigation scheduling and the determination of energy transfer, transpiration rate, and stomatal conductance in both single leaves and plant canopies.
Includes Solar Radiation protector AI-100.


This gradient is often less than 1 oC, which means that leaf temperature should be measured to within 0.1 oC.

To achieve this accuracy, we measure and correct for changes in the sensor body temperature.

Other Models available:
SI-122 with air purge (add 60€)
SI-131 Ultra Narrow Field-of-View Infrared Radiometer Sensor (no added price)
SI-1H1 Horizontal Field-of-View Infrared Radiometer Sensor (no added price)

Apogee infrared radiometers are the most accurate non-contact temperature sensors available anywhere.
The SI-121 has a 18 degree half angle field of view. The sensor has tinned leads for connecting to a datalogger.
Applications include measuring the temperatures of road surfaces, plant canopies, and soil, snow and water surfaces. Measurement of surface temperature is a crucial component of energy transfer.
Accurate measurement of the leaf-to-air temperature gradient is essential to the determination of transpiration rate and stomatal conductance in both single leaves and plant canopies.

Approximate Sensitivity: 40 μV per 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 (-20 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: < 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: 0.2 s
Field of View: 18° half angle
Spectral Range: 8 to 14 μm; atmospheric window
Operating Environment: -55 to 80 C, 0 to 100 % relative humidity (non-condensing)
Dimensions: 2.3 cm diameter and 6.0 cm length
Mass: 190 g (with 5 m of lead wire)
Cable: 5 m of four conductor, shielded, twisted-pair wire. Additional cable available in multiples of 5 m. Santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions). Pigtail lead wires.
Warranty: 4 years

The AI-100 radiation shield improves the performance of Apogee infrared sensors in applications where there is a significant solar load on the sensor housing.
This shield is included on all new infrared sensors and is offered as an accessory for customers wishing to retro-fit previously purchased infrared sensors.

Solar Radiation Protector AI-100
Incluided with every SI-121 order


Apogee AM-210 Bracket

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