Copyright 2013 Optical Sensors
Passive Cloud Cover Detector - PCCD
This innovation makes it possible to get automatic observations of the Cloud Cover Factor, CCF 24 hours a day. It consists of a day time unit that observes the sky in 4 directions in parts of the solar spectrum, a night time unit that observes the sky in the thermal infra red spectrum. A microcomputer evaluates  the signals and controls the output.
Real time data from a PCCD located in Göteborg, Sweden can be seen here.

Short data for the unit:
Approx size:                  22*13*15 cm
Power supply:               12 Volt DC
Current consumption:   about 2 mA for electronics and about 50 mA for heating
Temperature range:     -20 to +70 deg C
Output:                          Analog 0 to 1V, for CCF 0 to 100%.
                                      Alt: digital RS232 polled or streaming