SR20-T2-L ISO Secondary Standard Pyranometer
High Measurement Accuracy
Ideal for PV system performance monitoring
weather applications water applications energy applications gas flux & turbulence applications infrastructure applications soil applications


The SR20-T2, manufactured by Hukseflux Thermal Sensors, is an ISO 9060 secondary-standard pyranometer that measures solar short-wave radiation in a full hemisphere of the sky. It has a built-in case temperature sensor and embedded heater for removing dew and light rain. It connects directly to a Campbell Scientific datalogger and is designed for applications that require high measurement accuracy in demanding applications such as scientific meteorological observation networks and utility scale solar-energy-power production sites.

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Benefits and Features

  • Low temperature dependence
  • Embedded 1.5 W heater to reduce effects of dew deposition
  • Embedded 10K temperature sensor
  • Ultra robust connector, desiccant holder, and sun screen
  • Temperature dependence characterized and supplied for each instrument
  • Directional response tested on each instrument

The manufacturer offers a product brochure and a user manual.


Detailed Description

The SR20-T2 pyranometer measures the hemispherical solar radiation received by a plane surface, in W/m2, from a 180° field of view. The SR20 can be deployed indoors with lamp-based solar simulators or more commonly outdoors under the sun. Its orientation depends on the application and may be installed horizontally, tilted for plane or array irradiance, positioned on a sun tracker with shadow-ring for diffuse measurements, or inverted for reflected radiation.

The SR20-T2’s low temperature dependence makes it an ideal candidate for use under very cold and very hot conditions. The temperature dependence of each instrument is tested and supplied as a second-degree polynomial. This information can be used for further reduction of temperature dependence during post-processing.

The SR20 is equipped with an internal temperature sensor. Campbell Scientific supplies the T2 version, which has a 10 kohm thermistor. The T1 version, in contrast, has a PT100 and is available upon request. 

The embedded heater reduces measurement errors caused by early-morning dew deposition. Campbell Scientific recommends using the instrument in accordance with the recommended practices of ISO, WMO and ASTM.

The output of the SR20-T2 is analog. The SR20-D2-L model, in contrast, offers two other types of commonly used irradiance outputs: digital via Modbus RTU over 2-wire RS-485, and analog 4 to 20 mA output (current loop).


Measurements Made Hemispherical solar radiation
ISO 9060 Classification Secondary standard pyranometer
WMO Performance Level High-quality pyranometer
Response Time 3 s (95%)
Zero Offset A 5 W/m2 (unventilated), 2.5 W/m2 (ventilated) (response to 200 W/m2 net thermal radiation)
Zero Offset B ≤ -2 W/m2 (response to 5 K/h change in ambient temperature)
Non-Stability ≤ -0.5% change per year
Non-Linearity ≤ -0.2% (100 to 1000 W/m2)
Directional Response < ±10 W/m2
Spectral Selectivity < ±3% (0.35 to 1.5 x 10-6 m)
Temperature Response < ±1% (-10° to +40°C), < 0.4% (-30° to +50°C) with correction in data processing
Tilt Response < ±0.2% (0 to 90° at 1000 W/m2)
Heater 1.5 W (at 12 Vdc)
Steady-state Zero Offset 0 to -8 W/m2 (caused by heating)
Calibration Uncertainty < 1.2% (k=2)
Level Accuracy < 0.1° (bubble entirely in ring)
Sensor Resistance Range 100 to 200 ohm
Operating Temperature Range -40° to +80°C
Field of View (FOV) 180°
Measurement Range 0 to 4000 W/m2
Sensitivity Range 7 to 25 x 10-6 V/(W/m2)
Spectral Range 285 to 3000 x 10-9 m (20% transmission points)



CR1000 CR3000 CR5000

CR7X CR9000X CR6 CR300


The SR20-T2 is compatible with the following mounts: 27065, CM225, CM255, and CM255LS.

Power Considerations

The SR20-T2 heater is a 1.5 W heater at 12 Vdc. The SW12 power out port on the CR800/850, CR1000, and other dataloggers can supply the needed 0.125 A for the heater, as that port can supply 0.9 A at 20°C. More typically, relays controlled by the datalogger digital I/O ports are used to control the power supply.