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DR20-A1 pyrheliometer

Analogue spectrally flat Class A pyrheliometer, with heating

DR20-A1 is a high-accuracy direct (normal incidence) solar radiation sensor, or pyrheliometer. DR20 pyrheliometer complies with the Class A specifications of the ISO 9060 standard. It has a better temperature response than DR15-A1, which is a spectrally flat Class B pyrheliometer. These instruments are used in tracker-mounted operation, and offer analogue millivolt outputs. DR-series pyrheliometers have superior window heating that leads to high data availability.


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Hukseflux model DR20 pyrheliometer is an ISO 9060 spectrally flat Class A instrument. Together with DR15 pyrheliometer, it replaces the models DR01, DR02 and DR03. DR20 has a better temperature response than DR15. Both instruments offer the highest accuracy and highest data availability, featuring window heating at low offsets. At the same heating power, the heating has been improved with a factor 4, at a 4 times lower offset!
DR20 pyrheliometer is applied in high-accuracy measurement of the solar radiation received by a plane surface from a 5 ° full field of view angle. This quantity, expressed in W/m², is called “direct” solar radiation or DNI (direct normal irradiance). It is necessary to keep the instrument pointed at the sun by using a two-axis tracker.
A pyrheliometer is used in tracker-mounted operation. DR20-A1 can be connected directly to commonly used data logging systems. It offers analogue output in the millivolt range. The pyrheliometer features a precision ground and polished quartz window, a compact sized collimated tube and a thermopile sensor with black coated surface. High data availability is attained by heating of the front window. This suppresses dew and frost deposition at a very low power consumption: DR20 needs only 1 W to keep its window free from dew and frost.
Using DR20 / DR15 pyrheliometers offer significant benefits over the use of competing models. The pyrheliometers offer the highest accuracy and highest data availability, featuring heating at low offsets. The advantages of having a heater are demonstrated in graphs in the DR20 brochure (PDF).
As required by ISO 9060 for Class A classification, each DR20 is supplied with test results for the individual instrument:

  • sensitivity
  • response time
  • temperature response


Measurand direct solar radiation
ISO classification spectrally flat Class A
Calibration uncertainty < 1.2 % (k = 2)
Heating included
Heater 1 W at 12 VDC
Response time (95 %) 4 s
Full field of view angle 5 °
Slope angle 1 °
Zero offset < ± 1 W/m²
Calibration traceability to WRR
Spectral range 200 to 4000 x 10⁻⁹ m
Rated operating temperature range -40 to +80 °C
Temperature response < ± 0.5 % (-10 to +40 °C)
Temperature response < ± 0.4 %  (-30 to +50 °C) with correction in data processing
Calibration certificate included
Temperature response test of individual instrument report included
Standard cable length 5 m


Suggested use

  • solar energy surveys
  • solar resource assessments
  • meteorological networks
  • sites with dew and frost problems
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