Apogee Instruments


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The SI-111 22º 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 5m cable & 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.

The SI-111 comes with a standard 5 meter cable. Other Models with different cable length available (choose in 'Options'):
SI-111-L-10 Infrared Radiometer with Standard Field-of-View and 10 meter cable.
SI-111-L-15 Infrared Radiometer with Standard Field-of-View and 10 meter cable.
SI-111-L-20 Infrared Radiometer with Standard Field-of-View and 10 meter cable.

Apogee infrared radiometers are the most accurate non-contact temperature sensors available anywhere.
The SI-111 has a 22 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: 60 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: 22° 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
Included with every SI-111

Protector AI-100


Apogee Mast Bracket AM-210

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