Spectrally Flat Class A (secondary standard) pyranometer
PCTRA072 pyranometer is intended for solar radiation measurement on a plane/level surface (Watt/m²). The radiation measured is the sum of direct sun and of diffuse irradiance (global radiation).PCTRA072 uses a Spectrally Flat Class A (secondary standard) ISO 9060 pyranometer and it complies with WMO "Guide to meteorological Instruments and Methods of Observation", 5th edition (1983).
The pyranometer is based on a thermopile sensor. The sensing surface of the thermopile is coated with an opaque black paint providing a flat spectral response for the full wavelength range. The pyranometer spectral range is determined by the transmission of the dome made of special material that allows an extension of the spectral range up to 283nm.
The irradiance energy is absorbed by the blackened surface of thermopile providing a temperature difference between the centre of the sensor (hot junction) and the body of the pyranometer (cold junction). This difference is then converted to a voltage according to the Seeback effect.
PCTRA072 has two domes with 50 and 30 mm external diameter to guarantee correct thermal insulation from wind and to reduce sensitivity to thermal radiation. The dome protects the thermopile from dust which could modify spectral sensitivity. PCTRA072 is then provided with a bubble level for the correct levelling of the sensor.
A second thermopile is mounted inside the instrument and not accessible by light. This second thermopile, connected antiseries with respect to the sensor exposed to light, reduces the signals of the pyranometers caused by sudden temperature changes (thermal shock).
In order to minimize variations of sensitivity according to the temperature, the sensor are eqipped with a passive compensation circuit.
To avoid condense formation on the inner surface of the dome, moisture absorbing silica-gel is put inside the pyranometer.
The PCTRA076 is equipped with an adjustable shadow ring for the measurement of diffuse radiation only.
Spectrally Flat Class A (secondary standard) pyranometer
