introduction
The star pyranometer in its current form was developed by Dirmhirn. It belongs to the group of "black-and-white surface pyranometers" among meteorological radiation measuring instruments and is used to measure global radiation, sky radiation, shortwave reflected radiation, and shortwave radiation on variously oriented and inclined surfaces. Global radiation is the radiation incident on a horizontal surface from the upper hemisphere in the wavelength range of the solar spectrum from 0.3 to 3 μm, and is the sum of direct solar and diffuse sky radiation. Pyranometers do not measure radiation intensity directly, but indirectly via a temperature difference generated by the radiation. In electrical pyranometers, this difference is converted into a proportional electromotive force using a thermocouple. In this way, the complex measurement of a radiation current is reduced to the simple measurement of an electrical voltage. Global radiation, an important measurement parameter in environmental research, must be able to be determined under a wide range of weather conditions, so only a correspondingly robust and corrosion-resistant design of the measuring device can guarantee trouble-free operation.
Description
The radiation-sensitive surface of the star pyranometer consists of 12 circularly arranged copper plates, painted alternately black and white. When exposed to radiation, the black plates heat up more than the white ones. This temperature difference is measured using the thermopile attached to the underside of the plates. The voltage developed by this thermopile is approximately 15 μV/Wm-2 with an internal resistance of approximately 35 ohms. A glass dome made of ground optical "SCHOTT" glass is provided to protect the receiving surface. This dome is tightly connected to the housing by two sealing rings and a screw ring. A drying container filled with silica gel prevents condensation inside the device. A white-painted metal housing protects the drying container and prevents the instrument from overheating. The connecting cable is connected via a watertight screw connection, thus sealing the interior from ambient air. Three adjustment screws on the housing tabs and a spirit level are provided for leveling the device.
maintenance
The glass domes of star pyranometers in continuous use should be wiped clean and dry at least once a day. Ice deposits must be carefully removed, using de-icing spray if necessary. When measuring during the winter months, the instrument should be ventilated and heated to prevent fogging of the glass due to solid or liquid precipitation. The "Ventilation Housing Model No. 8106" is ideal for this purpose. Horizontal positioning should be checked daily if possible. The receiver surfaces must always be black and white. Should any irregularities or other defects appear on the receiver surfaces, an inspection at our factory is essential. Scratching of both the receiver surfaces and the glass dome must be avoided at all costs. Located on the underside of the star pyranometer is the removable drying container, which is filled with silica gel. This drying agent must always be red. If the agent appears pale, it must be replaced. If no new filling is available, the substance can be reactivated at a temperature of 80°C.
calibration
Pyranometers in continuous use should be calibrated at least every two years; annual calibration is recommended. This calibration also includes the annual seal replacement. The supplier will be happy to perform this service for you.
Options, spare parts
- Ventilation housing model 8106 for ventilating and heating the star pyranometer to prevent fogging of the dome in cold weather and cooling in warm weather
- glass dome
- 1 set of seals (3 pieces)
- Silica gel container with filling
