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

SF-421-SS: SDI-12 Leaf and Bud Temperature Sensor

The SF-421-SS has an SDI-12 digital output. The detector is a combination of two temperature sensors (precision thermistors) in a single housing. One sensor is designed to mimic a plant leaf the other a flower bud.

The SF-421-SS provides close approximations to leaf and bud temperatures and has a temperature measurement range of -50 to 70°C. Typical applications include leaf and bud temperature estimates in cropped fields, orchards, and vineyards. Leaf and bud temperatures returned by the detector can then be used to alert growers to the potential of frost damage to crops. Sensor includes IP68 marine-grade stainless-steel cable connector 30 cm from head to simplify sensor removal and replacement for maintenance and recalibration.


Utilising the SF-421 Sensor in a custom IoT (Internet of Things)

The SNiP-LBT is a ‘Sensor Node Integrated Package’ for LoRaWAN or CATM-1 communication of real-time leaf and bud temperature measurements, for continuous plant, light and environmental monitoring.

The base SNiP-LBT integrates 1x SF-421 Sensor and 1x S-NODE to a site’s unique network, communication and power requirements.

Frost damage to plants can have large impacts 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 and flower bud temperatures can drop below freezing even if air temperature remains above 0°C. This is called a radiation frost and is due to 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.

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
Non-stability (Long-term Drift): Less than 0.2°C per year (when used in non-condensing environments where the annual average temperature is less than 30°C; continuously high temperatures or continuously humid environments increase drift rate)
Equilibration Time: 10 s
Response Time: Fastest data transmission rate for SDI-12 circuitry is 1 s
Self-heating: Less than 0.01°C
Operating Environment: -50 to 70°C, 0 to 100% relative humidity
Input Voltage Requirement: 5.5 to 24 V DC
Current Drain: 0.6 mA (quiescent), 1.3 mA (active)
Dimensions: 570 mm length, 21 mm pipe diameter, 70 mm disk diameter
Mass: 400 g
Cable: 5 m of two conductor, shielded, twisted-pair wire with santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions), additional cable available
Warranty: 4 years against defects in materials and workmanship