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Leaf and Bud Temperature -SF 421

Make: Appogee                                      Model: SF-421
✅ Leaf and bud temperature estimates in cropped fields, orchards, and vineyards.
✅ Measurand : Temperature Response
✅ Sensor Type : Radiation Frost Detector
✅ Signal Output : Analog and digital output options include an unamplified voltage output or SDI-12 communication protocol.
✅ Supplied with : Cable, Factory test/ Calibration Certificates.

Leaf and Bud Temperature -SF 421:

The SF-110 (formerly called the leaf and bud temperature sensor) underwent a redesign to improve performance and ruggedness. As part of this redesign, the bud temperature sensor was removed, as it was determined the leaf measurement was most critical. The SF-110 was renamed the radiation frost detector.
Frost damage to plants can have a large impact on crop yield and quality. Protection of crops during frost events is dependent on the accuracy of plant temperature predictions. Often, air temperature is not a reliable predictor of timing, duration, and severity of frost events because plant canopy temperatures can be significantly different than air temperature under certain environmental conditions.
On clear, calm nights, plant leaf temperature can drop below freezing even if air temperature remains above 0 C.This is called a radiation frost and is caused by the lack of air mixing (wind) near the surface and a negative net longwave radiation balance at the surface (more longwave radiation is being emitted from the surface than what the surface is absorbing from the clear sky). Under cloudy and/or windy conditions, radiation frost events do not occur.
Apogee model SF-110 radiation frost detectors are designed to approximate plant leaf temperatures for prediction of frost events. SF-110 radiation frost detectors are intended for applications in cropped fields and orchards when air temperatures will be near freezing and where air temperature measurements are not a good predictor of frost formation.
Apogee Instruments SF-110 radiation frost detectors consist of a precision thermistor combined with a simulated leaf. The sensor is designed to mimic a plant leaf. SF-110 radiation frost detectors provide close approximations of leaf temperature and can be used to predict frost on leaves. The detector is weatherproof and designed for continuous temperature measurement in the same environmental conditions to which plants are exposed. The SF110 detector outputs one analog voltage signal (when supplied with an input voltage) that is related to the resistance of a thermistor. The resistance is directly related to simulated leaf temperature.

The SF-421-SS has an SDI-12 digital output and high-quality cable terminating in pre-tinned pigtail leads for easy connection to dataloggers and controllers. The detector contains a precision thermistor that mimics a leaf.

The SF-421-SS provides close approximations of leaf temperatures and has a temperature measurement range of -50 to 70 °C. Typical applications include leaf temperature estimates in cropped fields, orchards, and vineyards. Leaf temperatures returned by the detector can then be used to alert growers to the potential for frost damage to crops.

To facilitate sensor removal and replacement for maintenance and calibration, the sensor includes an IP68 marine-grade stainless-steel cable connector 30 cm from the head. While most users choose to mount the SF-411-SS to a branch or stick using zip ties, the AM-260 mounting fixture can be used as a more permanent mounting option.

Application and features of Leaf and Bud Temperature -SF 421:



✅ Agriculture
✅ Floriculture
✅ Study of phytopathogen models forecasting
✅ Thermistor accuracy is ± 0.1 C across a range of 0 to 70 C
✅ Providing accurate measurements at temperatures near zero where frost damage is likely to occur.
✅ Analog and digital output options include an unamplified voltage output or SDI-12 communication protocol.

Apogee Instruments



General Specification


Weight (Mass)

400 g


570 mm length, 21 mm pipe diameter, 70 mm disk diameter


⦿ Input Voltage Requirement: 5.5 to 24 V DC
⦿ Current Draw: 0.6 mA (quiescent), 1.3 mA (active)

Measuring Range

⦿ Measurement Range: -50 to 70 C
⦿ Measurement Uncertainty: 0.1 C (from 0 to 70 C), 0.2 C (from -25 to 0 C), 0.4 C (from -50 to -25 C)
⦿ Measurement Repeatability: Less than 0.05 C

Operating Environment

-50 to +70 C/ 0 to 100 % relative humidity


4 years against defects in materials and workmanship

Quote Leaf and Bud Temperature -SF 421