The SP-230 (All-season) is a heated pyranometer with a 0.2 W heater to keep water (liquid and frozen) off the sensor and minimize errors caused by dew, frost, rain, or snow blocking the optical path. Sensor includes IP67 marine-grade stainless-steel cable connector 30 cm from head to simplify sensor removal and replacement for maintenance and recalibration.
Figure 1: Solar radiation after a January frost in Logan, Utah with overcast conditions until 11 a.m. The two replicate Apogee SP-230 pyranometers were nearly identical to a heated and ventilated reference pyranometer. In spite of the bright sunlight after 11 a.m., the frost on two unheated glass dome thermopile and four replicate unheated castle design pyranometers did not melt until after 4 p.m. (1600 hours).
Figure 2. The effect of frost and snow accumulation for three groups of pyranometers in Logan UT, expressed as a percentage of true reading. Castle design and unheated thermopile sensors averaged a 20% error for the month with a maximum error of 80%. Data for Figure 1 is from day 12.
Power Supply 12 V DC for heater with a current draw of 15.4 mA
Heater 780 Ω, 15.4 mA current draw and 185 mW power requirement at 12 V DC
Sensitivity 0.2 mV per W mˉ²
Calibration Factor (reciprocal of output) 5 W mˉ² per mV
Calibration Uncertainty ± 5 %
Calibrated Output Range 0 to 400 mV
Measurement Repeatability Less than 1 %
Non-stability (Long-term Drift) Less than 2 % per year
Non-linearity Less than 1 % (up to 2000 W mˉ²)
Response Time Less than 1 ms
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 ± 0.04 % 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 24 mm diameter, 28 mm height
Mass 90 g (with 5 m of lead wire)
Warranty 4 years against defects in materials and workmanship