Physikalisch-Metorologisches Observatorium Davos -- World Radiation Center pmod-wrc


An absolute cavity radiometer system for measuring the direct solar irradiance.

General Specifications
The PMO6-CC is a self-contained system designed to measure the direct solar irradiance. It consists of a radiometer head (absolute cavity pyrheliometer) and a control unit.
The heart of the radiometer head is a blackened cavity in which the solar radiation is absorbed. It was developed at PMOD/WRC and is of the same type as the earlier PMO6 instrument series.
The PMO6-CC control unit (“CC” stands for “Computer Controlled”) is a development of the Davos Observatory aimed at providing the largest possible freedom and convenience to operate the system either manually or remotely controlled from an external computer. It contains an internal PC and voltmeters to conduct measurements and to communicate with the user using its display and touch-panel or its RS232 port.

Principle of operation
Absolute radiometers are based on an electrically calibrated heat flux transducer and a cavity as receiver. The cavity ensures high absorption over the spectral range of interest. The principle of the measurement relies on the substitution of the radiant power by electric power. During operation of the instrument, an electronic circuit maintains a constant heat flux from the cavity heater by adjusting the input power. The heat flux is measured differentially between two cavities in order to compensate for the rate of change of the heat sink’s temperature.

Traceability to WRR
Each unit is compared to the World Standard Group to provide direct traceability to the World Radiometric Reference.

The standard mode of operation of the radiometer consists of alternate measurements with the shutter closed and open. The duration of each phase (closed and open) may be chosen (default: 60 seconds). The number of cycles and the integration time are also free parameters. The start time of the measurements can be set to a predefined time. After every open/closed cycle, the irradiance is shown on the display and sent out to the RS232 port.
After completion of a measurement series, all the irradiances of the series can be read on the display or downloaded using the RS232 port.

Functionality check, configuration, …
Various dialog modes are provided to check the functionality of the H/W as shutter, A/D, housekeeping, to set the date and time and to implement the instrument parameters

Contact address
Dr. Wolfgang Finsterle, e-mail: w.finsterle(at) , phone: +41 58 467 51 53


PMO6-CC Radiometer
Dimension: 80 x 80 x 230 mm
Mass: 2.15 kg
Field of view (full angle):
Slope angle:
Range: up to 1400 W/m2 (Or custom design available)
Traceability to WRR: < 0.1%
Operating temperature range: -25 °C … +50 °C

PMO6-CC Control Unit
Dimension: 280 x 270 x 85 mm
Mass: 3 kg (approx.)
Power requirement 8.5 W
Accuracy: Absolute measurement uncertainty is less then 50ppm of radiometer full-scale range;
Outputs: Analog: ± 10 V
Digital: RS232, 9600Bd, 8 Bit, non Parity, 1 Stop
Operating temperature range: 10 °C … +40 °C
Dorfstrasse 33, CH-7260 Davos Dorf, Phone +41 58 467 51 11, Fax +41 58 467 51 00