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SR20-D2 pyranometer

Digital secondary standard pyranometer with Modbus RTU and 4-20 mA output

SR20-D2 is a solar radiation sensor of the highest category in the ISO 9060 classification system: secondary standard. SR20-D2 is designed for the solar PV industry, offering two types of commonly used irradiance outputs: digital via Modbus RTU over RS-485 and analogue 4-20 mA (current loop). These industry standards allow for easy data acquisition, easy read-out and error-free instrument exchange, when using SR20-D2. Individually tested for temperature and directional response, SR20-D2 is the most accurate digital secondary standard pyranometer available.

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Best pyranometer for the PV industry

SR20-D2 is the most accurate digital secondary standard pyranometer available. Its benefits:

  • Digital output: easy implementation & servicing
  • Best-in-class temperature response, < ± 0.4 % (-30 to +50 °C), best “zero offset a” and best calibration uncertainty
  • Test certificates for temperature response and directional response included as required by ISO 9060
  • Re-calibration registers fully accessible to users

In order to improve overall measurement accuracy, Hukseflux effectively targeted two major sources of measurement uncertainty: calibration and “zero offset a”.
In addition, SR20-D2 has a negligible temperature response. All are best in class. The temperature response of every individual instrument is tested and corrected onboard by the instrument electronics, using a second degree polynomial. SR20-D2’s low temperature dependence makes it the ideal candidate for use under very cold and very hot conditions.

SR20-D2 pyranometer design

The pyranometer employs a state-of-the-art thermopile sensor with black coated surface, two domes and an anodised aluminium body. The connector, desiccant holder and sun screen fixation are very robust and designed for long term industrial use. SR20-D2 uses a high-end 24-bit A/D converter. All parts are specified for use across SR20-D2’s entire rated operating temperature range. SR20-D2 offers two types of outputs commonly used in the solar PV industry: digital output via Modbus RTU over 2-wire RS-485 and analogue 4-20 mA output (current loop).


Measurand hemispherical solar radiation
ISO 9060:2018 classification spectrally flat Class A (secondary standard)
IEC 61724-1:2017 compliance Class A (when used with VU01)
Application PV monitoring commercial and utility scale
Heater no
Output 4-20 mA current loop
Calibration uncertainty < 1.2 % (k = 2)
Zero offset a 5 W/m² unventilated and 2.5 W/m² ventilated
Calibration traceability to WRR
Calibration registers accessible to users
Spectral range 285 to 3000 x 10⁻⁹ m
Rated operating temperature range -40 to +80 °C
Temperature response < ± 0.4 %  (-30 to +50 °C)
Heater no heating
Temperature response test of individual instrument report included
Directional response test of individual instrument report included
Standard cable length 5 m
Backwards compatibility SR20-D1
Digital output :
Output irradiance in W/m² and instrument body temperature in °C
Communication protocol Modbus / over 2-wire RS-485
Transmission mode RTU
Rated operating voltage range 5 to 30 VDC
Power consumption < 75 x 10⁻³ W  at 12 VDC
4-20 mA output :
Output irradiance in W/m²
Transmitted range of 4-20 mA output 0 to 1600 W/m²
Rated operating voltage range of 4-20 mA output 5.5 to 40 VDC
Power consumption :
main supply < 75 x 10⁻³ W
4-20 mA current loop < 40 x 10⁻³ W at 12 VDC
  • longer cable, in multiples of 5 metres
  • adapted transmitted range for 4-20 mA output
  • ventilated with VU01 ventilation unit


Suggested use

  • PV system performance monitoring
  • all networks with regular instrument exchange
  • scientific meteorological observations
  • reference instrument for comparison
  • extreme climates (tropical / polar)
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