EKO INSTRUMENTS CO., LTD. MS-56 Pyrheliometer Manual Ver.5
Pg. 17
6 - 2 . C a l i b r a t i o n a n d M e a s u r e m e n t U n c e r ta i n t y
It is recommended to recalibrate the instrument once every 2 years. For further information about the
calibration and recalibration, please contact EKO.
1. Calibration Method
The MS-56 is calibrated under natural sun light against the EKO instruments reference pyrheliometer which is
traceable to the World Radiation Reference (WRR) maintained at the World Radiation Center (PMOD) in
Davos (CH).
Both MS-56 and reference pyrheliometer are mounted on a Sun Tracker to capture the direct solar radiation.
The direct solar radiation is measured based on 1 minute samplings for total of more than 2 hours both in the
morning and the afternoon on a clear day. The calibration value of the subjected pyrheliometer was obtained
by multiplying the sensitivity value [
μV/W
･
m
-2
] of the reference pyrheliometer with the averaged ratio of the
measured total direct irradiance data. To improve the calibration accuracy and minimize the measurement
uncertainty several operating criteria are applied.
2. Calibration Uncertainty and Traceability
The criteria for the operating conditions like the indicated ambient temperature, minimum direct radiation and
minimum solar elevation angle are applied to minimize the overall uncertainty in the calibration. The
pyrheliometer uncertainty figure is statistically calculated based on a standard deviation of (1.96
σ), which
means that 95% of the measured direct irradiance values agree with the reference pyrheliometer.
The reference pyrheliometer will be calibrated at ATLAS/DSET
every 2 years against a primary standard
pyrheliometer, called absolute cavity pyrheliometer. The ATLAS/DSET absolute radiometer is directly
traceable to the WRR (World Radiometric Reference) and maintained in the group of standard radiometers
calibrated every 5 years during the IPC (International Pyrheliometer Comparison), as well as by NPC (NREL
Pyrheliometer Comparison) which is held every year.
The data acquisition system is traceable to JEMIC (Japan Electric Meters Inspection Corporation).
