Function blocks TS3900 14 Version: 1.1 stTime The date and the local time are specified via stTime. This structure is of type ST SPA TIMESTRUCT [} 18]. fTimezone _ _ The required date with the corresponding time can be specified in local time via the above variable. The respective time zone is added via fTimezone. The time zone is always based on Greenwich (London). (The prime meridian, i.e. 0° geographic longitude, also passes through Greenwich). The following applies in relation to the coordinated world time: UTC+1 = Central European Time; UTC+2 = Central European Summer Time. fDelta t _ The input variable fDelta t is used for balancing _ the time scales used. A standard value is 66.
A more detailed description of the different time scales can be found on the overview page [} 8]. fLongitude fLongitude indicates the longitude in degrees [°]. It is positive to the east of Greenwich. fLatitude fLatitude indicates the latitude in degrees [°]. It is positive to the north of the equator and negative to the south. fElevation The altitude of the location also has a small effect on the calculation of the sun angles. fElevation indicates the height in metres above mean sea level. fPressure The atmospheric pressure at the location is specified in millibar [mbar] via the input variable fPressure. The annual average is specified.
fTemperature The temperature at the location is specified via the input variable fTemperature in °C. The annual average is specified. fSlope Via fSlope a surface inclination can be specified in degrees [°]. It is used for calculating the special angle of incidence fIncidence. If fSlope is zero, the angle of incidence is the same as the zenith angle. fAzm rotation _ fAzm rotation can be used to adjust the alignment _ (in degrees [°]) of the observer or the surface inclined by fSlope. For north alignment the value is 0°. From there the alignment angle increases clockwise (positive values, as does the azimuth of the sun angle).
It is also used for calculating the special angle of incidence fIncidence. Is fSlope is zero, the angle of incidence is the same as the zenith angle, irrespective of fAzm rotation. If _ fAzm rotation is the same as the sun angle _ fAzimuth, the following applies: fIncidence = fZenith + fSlope. This is illustrated the following 2D diagram. fAtmos refract _ Refraction in the atmosphere can have a significant effect on the zenith angle of the sun, particularly for shallow sun angles. The input variable fAtmos refract is used as a correction _ factor for the atmospheric distraction at sunrise and sunset. A standard value is 0.5667.