SR20-D2 pyranometer

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

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SR20-D2 digital pyranometer

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. It measures the solar radiation received by a plane surface, in W/m2, from a 180o field of view angle.

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-D1’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).

Re-calibration: accessible registers

The recommended calibration interval of pyranometers is 2 years. The registers containing the applied sensitivity and the calibration history of SR20-D2 are fully accessible for users. This allows the user to choose his own local calibration service. The same feature may be used for remotely controlled re-calibration of pyranometers in the field. Ask Hukseflux for information on this feature and on ISO and ASTM standardised procedures for field calibration.

Sensor Manager software

For communication between a PC and SR20-D2, the Hukseflux Sensor Manager software is included. It allows the user to plot and export data, and change the SR20-D2 Modbus address and its communication settings. The latest Hukseflux Sensor Manager software for SR20-D2 is available for download here.

Suggested use

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


  • longer cable, in multiples of 5 metres
  • adapted transmitted range for 4-20 mA output
  • ventilated with VU01 ventilation unit

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