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Original factory packaging
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Instrument Expert
Original factory packaging
Service Hotline：
(+86)010-52867771
Updated:2025-03-13
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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 Drawing
| 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 |
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