Kipp&Zonen BSRN Scientific Solar Monitoring System - Manual (Page 62)

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- for friction-driven drives check for slippage of the drive disks (see tracker operating
m anual for the proper procedure).
- if slippage occurs on gear driven trackers, the gears should be inspected for m issing
teeth and the gear alignm ent tested (see 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.
The operator should always note the position of the solar spot on the pyrheliom eter or cavity
radiom eter before any adjustm ent is m ade. Following the adjustm ent, the new location of
the solar spot should be noted. The tim e required to m ake the adjustm ent and the details
of what caused the failure to track and its correction should also be docum ented.
(8) Cavity Radiom eters
(i) All-weather instruments: Cavity radiom eters m odified for continuous use should be
checked daily to ensure that all safety features are operating properly. These m ight
include such item s as autom atic shutters, rain sensors or fan switches. The m anufacturer’s
operating m anual should be consulted. Fans in continuous operation should be checked
for proper operation.
(ii) Fair-weather instruments: Instrum ents operated during fair weather conditions m ust
be checked for proper alignm ent and correct signal and power connections as part
of the set-up procedure. Shutters should be checked to ensure correct operation before
m easurem ents begin. Following use, the exterior of the instrum ent should be wiped
down and the entire instrum ent inspected for any dam age, including the lodging of
any insects within the instrum ent cavity. If the instrum ent is m oved into a heated enclosure
following the m easurem ent period, care should be taken to avoid m oisture condensing
in the cavity. Although the transducer coating is not water soluble, over tim e, chem ical
constituents within the condensing liquid can cause changes in the absorptance of
the coating. Cleaning of the sensor should be done only by qualified personnel.
(9) Shaded Instrum ents - Diffuse Irradiance, Infrared Irradiance
Each shaded instrum ent m ust be checked to ensure that the shading device com pletely covers
the outer dom e of the instrum ent. These checks are sim ilar to those above for the direct beam
instrum ents.
(10) Data acquisition/com puter system s
The system collecting the data should be checked to ensure that it is operational. The operator,
in conjunction with the site scientist, should devise appropriate m ethods to decide whether
the system is operational. Sim ply looking at a com puter screen is NOT sufficient. Tests should
be devised to detect that data are being acquired successfully, that the tim e stam p is correct
and that the system has not m alfunctioned since the last check.
A correct system tim e is crucial because data are being obtained at one second intervals.
Unfortunately, m any PC com patible com puters have very poor clock system s. Each day the
clock offset should be recorded and the tim e corrected if this offset is greater than one second.
If the clock varies by m ore than 10 seconds per day, a new clock should be installed. A system
changing at a rate of less than one second per m onth would be ideal (see section 2.3.1).
(11) W here possible, the site operator should be able to review the data from the previous day.
This inform ation will allow him /her to detect any significant changes that m ay have occurred
during the day. An exam ple of such a change would be a passive tracker that was not level.
During the m orning when the observer checks the shading of instrum ents it would be found
correct, but during the afternoon the diffuse flux would increase because of the shading disk
m oving off the sensor.