EKO INSTRUMENTS CO., LTD. Sunshine Duration Meter MS-093 Instruction Manual Ver.4
Pg. 15
6. Measurement
Principle
1. Sensor Head
The reflecting mirror inside the sensor head rotates 100 times per hour by pulse motor; direct solar radiation is
reflected onto the light receiving element which uses pyroelectric element in the rate of once per every 36 seconds.
This pyroelectric element outputs voltage which is proportional to the changes (micro coefficient) in the thermal
energy against this reflecting light.
2. Electric Circuit
Inside the analog circuit, the output from pyroelectric element is applied to the comparator circuit as it is enhanced
by the amplifier. The comparator circuit is setup with reference voltage, which is equivalent to the threshold value
(120W/m
2
) standardized by WMO (World Meteorological Organization), by adjusting the trimmer resistance; when
DNI (Direct Normal Incidence) exceeds this threshold value, it is determined as there is sunshine. Moreover, when
the logic circuit recognizes the “sunshine” from the logic values which determine either “sunshine” or “no sunshine”,
the non-voltage contact is made for one second; such measurement is processed once every 36 seconds, and its
result will be the output of Sunshine Duration Meter.
3. Reset Box
The reflecting mirror rotates at slow speed of 36 seconds cycle. This rotation movement is created by the
half-step drive method using 4-phase stepping motor, and there are cases that current runs through the 4 coils in
the stepping motor by 2-phases at once and by just 1-phase at once. These conditions are repeated by every
one step, thus the current flow in the power supply line fluctuates in constant cycle. By monitoring this current
fluctuation, it determines whether the mirror is rotating, and when the mirror stops, the power supply is reset to
automatically start the mirror operation.
4. Power Supply
A commercial power supply generates DC12V from AC100V~240V by switching power supply, then supply this
power to the MS-093.
