Kipp&Zonen BSRN Scientific Solar Monitoring System - Manual (Page 47)

35
(2) The synchronous m otor m ust:
(I) be wired appropriately the electrical power frequency of the location of installation,
(ii) be wired to follow the path of the sun (opposite for northern and southern hem ispheres,
(iii) be m ounted on a level baseplate,
(iv) be perpendicular to the horizon,
(v) be located equatorward of the pyranom eter,
(vi) be aligned true north-south,
(vii) be pointing poleward at an angle equal to the latitude of the site,
(viii) be in a position such that a line extending from the m otor axis pass through the centre
point of the instrum ent sensor.
(3) The cables of the pyranom eter (and ventilator) m ust be routed in a m anner that will not interfere
with the shade arm . In the Swiss case, this is done by having the shade arm able to rotate
about the stand on which the pyranom eter is located, while in the Germ an case the wires
are passed through the centre of the axis.
(4) The area around the instrum ent m ust be free of obstructions so that the arm can rotate a
full 360°. This includes the surface on which the instrum entation is m ounted.
Two-axes trackers can be used either as a m eans of shading one or m ore instrum ents or as a com bination
unit where a pyrheliom eter is also attached to the tracker. Figure 4.5 illustrates the Australian com puter-
controlled active-tracker on which the norm al incident direct beam is m easured using a pyrheliom eter
coincidentally with a pyranom eter being shaded with a shade-disk, while Figure 4.6 shows a Canadian
Figure 4.4. View of two Swiss oversize tracking disks. Note how
the pyranom eter is physically separated from the m otor and the
shade device. The increased width of the arm holding the shade
disk elim inates the need for stablilizing wires, but increases the
am ount of sky obscurred. The slot along the arm is for the
m ovem ent of the shade disk. On the instrum ent to the right of the
photograph, the vertical wires are used to deter birds perching on
the instrum ent. (Courtesy of MeteoSwiss, Payerne, Switzerland.)