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

SI-131 Ultra-Narrow FOV Infrared Radiometer

Apogee infrared radiometers are the most accurate non-contact temperature sensors available anywhere. The SI-131 has a 14 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.

If you are using any SI-100 series sensor with Campbell Scientific Dataloggers, please view the three notices from Campbell Scientific and Apogee to the right.

Model SI-131 FOV = 14.0°

The SI-100 series sensors measure the temperatures of road surfaces, plant canopies, and soil, snow and water surfaces.
• Measures surface temperature rapidly
• Calibrated target temperature range from -30 to 65°C
• Uncertainty of 0.2°C (95% confidence)
• 8-14 µm germanium atmospheric window
• Radiation shield included
• Multiple field of view (FOV) options
• Rugged and lightweight
Field of View (FOV) is reported as the half-angle of the apex of the cone formed by the target (cone base) and the detector (cone apex). The target is a circle from which 98% of the radiation being viewed by the detector is being emitted.

Approximate Sensitivity: 20 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: 0.2s
Field of View: 14° 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: 190g (with 5m of lead wire)
Cable: 5m of four conductor, shielded, twisted-pair wire. Additional cable available in multiples of 5m. Santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions). Pigtail lead wires.
Warranty: 4 years
  • AA-100: Protective Carrying Case
    Protective carrying case designed to transport and store Apogee meters, sensors, and accessories.
  • Infrared Radiometer/Frost Detector Mounting Bracket
    The AM-210 mounting bracket is designed to orient sensors at varying angles to satisfy all applications. The bracket can be mounted to a mast or pipe with an outer diameter of 1.3 to 2.1 inches, while the sensor bracket will accommodate sensors with an outer diameter of 1.0 to 1.5 inches (e.g. SI-100 series and SF-110).