| SF-110 | SF-421 | |
|---|---|---|
| Measurement Range | -50 to 70 C | -50 to 70 C |
| Measurement Uncertainty | 0.1 C (from 0 to 70 C), 0.2 C (from -25 to 0 C), 0.4 (from -50 to -25 C) | 0.1 C (from 0 to 70 C), 0.2 C (from -25 to 0 C), 0.4 (from -50 to -25 C) |
| Measurement Repeatability | Less than 0.05 C | Less than 0.05 C |
| Long-term Drift (Non-stability) | Less than 0.02 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) | Less than 0.02 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 | 10 s |
| Self-heating | Less than 0.01 C (typical, assuming pulsed excitation of 2.5 V DC), 0.08 C at 5 C (maximum, assuming continuous input excitation of 2.5 V DC) | Less than 0.01 C |
| Operating Environment | -50 to 70 C; 0 to 100 % relative humidity | -50 to 70 C; 0 to 100 % relative humidity |
| Input Voltage Requirement | 2.5 V DC excitation | 5.5 to 24 V DC |
| Output Voltage Range | 0 to 2.5 V DC (assuming input excitation of 2.5 V DC) | - |
| Current Draw | 0.1 mA DC (per thermistor) at 70 C (maximum, assuming continuous input excitation of 2.5 V DC) | 0.6 mA (quiescent), 1.3 mA (active) |
| Dimensions | 570 mm length, 21 mm pipe diameter, 70 mm disk diameter | 570 mm length, 21 mm pipe diameter, 70 mm disk diameter |
| Mass | 400 g | 400 g |
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 (see figure on following page). 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.
Apogee Instruments Leaf and Bud Temperature Sensors are designed to approximate plant leaf and flower bud temperatures for prediction of frost events. 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 leaf and bud temperature sensors consist of two precision thermistors, one combined with a simulated leaf and the other a simulated bud, in a single housing. The leaf sensor is designed to mimic a plant leaf and the bud sensor is designed to mimic a flower bud. Leaf and bud temperature sensors provide close approximations to leaf and bud temperatures and can be used for prediction of frost on leaves and buds. Detectors are weatherproof and are designed for continuous temperature measurement in the same environmental conditions plants are exposed to.
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.
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Helpful Articles and Links
Fruit Bud Damage from Cold Temperatures
Responding to Freezing Conditions
Frost/Freeze Protection for Horticultural Crops
Minimize Losses from Frost Using Direct Measurements - Campbell Scientific Post
Using Wireless Sensor Networks in Commerical Strawberry Production
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