Kipp&Zonen BSRN Scientific Solar Monitoring System - Manual (Page 61)

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(ii) Two-axes passive solar tracker
Passive trackers use either internal or external com puters to calculate the position of
the solar disk. Following the initial setup of the system , tracking of the solar spot by
the shading disk or the instrum ent attached to the tracker should not norm ally vary
except when the power is rem oved from the tracker and/or the com puter operating
the tracker, or when the tim e used to calculate the solar position is incorrect.
- check that the clock tim e used in the calculation of solar position is accurate to better
than 15 seconds for tracking of instrum ents with a 2° field of view or greater. The sm aller
the FOV, the greater the tim e accuracy required.
- on days when the solar spot is visible on the target, check tracker alignm ent. If not
aligned follow the procedures below and/or in the m anual.
- determ ine if the power to the tracker has been disrupted either at the m ain power
panel or within the cabling to and within the tracker.
- for friction-driven drives check for slippage of the drive disks (see the tracker operating
m anual for the proper procedure).
- for gear-driven drives, if slippage occurs, check gear alignm ent or if one or m ore gears
have broken teeth (see the tracker operating m anual for proper procedures).
- check to ensure that the tracker has not changed its physical position, either in level
or location (e.g., the tracker has not been bum ped accidentally).
- a tracker m echanical m alfunction or software failure can also cause a loss of tracking
capability. The operator should refer to the tracker operating m anual in such cases.
(iii) Two-axes active solar tracker
An active tracker corrects for sm all variations in the pointing of a passive system . Such
a system requires that the tracker not operate in active m ode during periods where
the solar signal is below a defined solar irradiance threshold. During such periods, the
active tracker should operate in a m ode sim ilar to a two-axes passive system . Following
the initial setup of the system , tracking of the solar spot by the shading disk or the
instrum ent attached to the tracker should not norm ally vary except when the power
is rem oved from the tracker and/or the com puter operating the tracker.
- clean the active sensing unit on the tracker daily and following occurrences of
precipitation.
- check that the clock tim e used in the calculation of solar position is accurate to better
than 15 seconds for tracking of instrum ents with a 2° field of view or greater. The sm aller
the FOV, the greater the tim e accuracy required.
- on days when the solar spot is visible on the target, check tracker alignm ent. If not
aligned follow the procedures below and/or in the m anual.
- determ ine if the power to the tracker has been disrupted either at the m ain power
panel or within the cabling to and within the tracker for a tim e greater than that which
the active sensing unit can correct.
- check the operation of the active sensing unit. This can be accom plished by covering
the active sensor and m anually positioning the tracker to within the acceptance lim its
of the active sensor with the power turned off. By turning on the power to the tracker
(ensuring that any com puter program s are operating correctly) the active sensor should
m ove the tracker into correct alignm ent. If this does not occur, technical assistance
in further checking the operation of the active sensor is required.