Spectrally Flat Class A Pyranometer with Sapphire Outer Dome

SR25 takes solar radiation measurement to the next level. Using a sapphire outer dome, it has negligible zero offsets. SR25 is heated in order to suppress dew and frost deposition, maintaining its high measurement accuracy. When heating SR25, the data availability and accuracy are higher than when ventilating traditional pyranometers. In addition, SR25 needs very low power; it only consumes 1.5 W compared to the usual 10 W for ventilation. The low thermal offsets make SR25 very suitable for measuring diffuse radiation.

  • Data availability is highly increased over traditional pyranometers
  • Needs very low power
  • SR25 is an excellent reference for diffuse radiation


Best Data Availability
By keeping the SR25 outer dome free of dew and frost with help of the internal heater, data availability is highly increased over traditional pyranometers, whether these are ventilated or not. The application photo shows the clear difference between SR25 versus a non-heated pyranometer without sapphire dome.

Best Measurement Accuracy
SR25 measures the solar radiation received by a plane surface, in W/m², from a 180 ° field of view angle. SR25 offers the best measurement accuracy: the specification limits of two major sources of measurement uncertainty have been greatly improved over competing pyranometers: “zero offset a” and temperature response.

SR25 Design
SR25 has a sapphire outer dome, glass inner dome and an internal heater. It employs a state-of-the-art thermopile sensor with black coated surface and an anodized aluminum body. The connector, desiccant holder and sun screen fixation are very robust and designed for long term use.

Suggested Use

  • Diffuse measurements
  • All situations where ventilated pyranometers are employed
  • PV system performance monitoring
  • Indoor PV testing with solar simulators
  • Airborne measurements
  • Diffuse measurements
  • Environments with dew
  • Environments with frost

Areas of Application

  • Meteorology / surface energy flux measurement
  • Solar energy / PV system performance monitoring


  • VU01
  • SHR02
  • PMF01
  • PMF02



hemispherical solar radiation

ISO 9060:2018 classification

spectrally flat Class A (secondary standard)

IEC 61724-1:2017 compliance

Class B


National Meteorological NetworksPV monitoring commercial and utility scale, meteorology / climatology, other





Zero offset a

1 W/m² unventilated

Calibration traceability

to WRR

Spectral range

285 to 3000 x 10⁻⁹ m

Sensitivity (nominal)

15 x 10⁻⁶ V/(W/m²)

Rated operating temperature range

-40 to +80 °C

Temperature response

<± 1 % (-10 to +40 °C), <± 0.4 % (-30 to +50 °C) with correction in dataprocessing

Temperature response test of individual instrument

report included

Directional response test of individual instrument

report included

Temperature sensor

Pt100 or 10 kΩ thermistor

Standard cable length

5 m

Version order codes

SR25-T1, SR25-T2


longer cable, in multiples of 5 metres


Download Product Brochure

Download Product Manual

SR25: diffuse solar radiation reference

SR25: The making of

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