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

SP-421 SDI-12 Silicon-cell Pyranometer

The SP-421 is a digital sensor with SDI-12 communication protocol. The sensor incorporates a silicon-cell photodiode with a rugged, self-cleaning sensor housing design. Typical applications include shortwave radiation measurement in agricultural, ecological, and hydrological weather networks. Sensors are also used to optimize photovoltaic systems.

Accurate, Stable Measurements

Calibration in controlled laboratory conditions is traceable to the World Radiometric Reference in Davos, Switzerland. Pyranometers are cosine-corrected with directional errors less than ± 5% at a solar zenith angle of 75°. Long-term non-stability determined from multiple replicate pyranometers in accelerated aging tests and field conditions is less than 2% per year.

Rugged, Self-cleaning Head

Patented domed shaped sensor head (diffuser and body) facilitate runoff of dew and rain to keep the diffuser clean and minimise errors caused by dust blocking the radiation path. Sensors are housed in a rugged anodised aluminium body and electronics are fully potted.

Mounting

The AM-110 mounting bracket facilitates mounting the AL-100 levelling plate to a mast or pipe. The bubble level in the plate makes levelling simple and accurate.

Output Options

Digital output option is an SDI-12 communication protocol. Sensor is also available in multiple analogue output options and attached to a hand-held meter with digital readout.

Typical Applications

Applications include shortwave radiation measurement in agricultural, ecological, and hydrological weather networks and solar panel arrays.

Input Voltage Requirement: 4.5 to 24 V DC
Current Drain: 0.6 mA (quiescent), 1.3 mA (active)
Calibration Uncertainty: ± 5%
Measurement Repeatability: Less than 1%
Long-term Drift (Non-stability): Less than 2% per year
Non-linearity: Less than 1% (up to 1750 W m-2)
Response Time: 0.6 s, time for detector signal to reach 95% following a step change; fastest data transmission rate for SDI-12 circuitry is 1 s
Field of View: 180°
Spectral Range: 360 to 1120 nm (wavelengths where response is 10% of maximum)
Directional (Cosine) Response: ± 5% at 75° zenith angle
Temperature Response: 0.04 ± 0.4% per °C
Operating Environment: -40 to 70°C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m
Dimensions: 44.0 mm height, 23.5 mm diameter
Mass: 117 g (with 5 m cable)
Cable: 5 m of two conductor, shielded, twisted-pair wire, additional cable available in multiples of 5 m; santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions); pigtail lead wires

Calibration Traceability

Apogee Instruments SP series pyranometers are calibrated through side-by-side comparison to the mean of four Apogee SP-110 transfer standard pyranometers (shortwave radiation reference) under high intensity discharge metal halide lamps. The transfer standard pyranometers are calibrated through side-by-side comparison to the mean of at least two ISO-classified reference pyranometers under sunlight (clear sky conditions) in Logan, Utah. Each of four ISO-classified reference pyanometers are recalibrated on an alternating year schedule (two instruments each year) at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. NREL reference standards are calibrated to the World Radiometric Reference (WRR) in Davos, Switzerland.