Kippzonen BSRN Scientific Solar Monitoring System Manual de usuario descargar pdf (Pagina 62)

- for friction-driven drives check for slippage of the drive disks (see tracker operating

manual for the proper procedure).

- if slippage occurs on gear driven trackers, the gears should be inspected for missing

teeth and the gear alignment tested (see tracker operating manual 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 bumped accidentally).

- a tracker mechanical malfunction or software failure can also cause a loss of tracking

capability. The operator should refer to the tracker operating manual in such cases.

The operator should always note the position of the solar spot on the pyrheliometer or cavity

radiometer before any adjustment is made. Following the adjustment, the new location of

the solar spot should be noted. The time required to make the adjustment and the details

of what caused the failure to track and its correction should also be documented.

(8) Cavity Radiometers

(i) All-weather instruments: Cavity radiometers modified for continuous use should be

checked daily to ensure that all safety features are operating properly. These might

include such items as automatic shutters, rain sensors or fan switches. The manufacturer’s

operating manual should be consulted. Fans in continuous operation should be checked

for proper operation.

(ii) Fair-weather instruments: Instruments operated during fair weather conditions must

be checked for proper alignment and correct signal and power connections as part

of the set-up procedure. Shutters should be checked to ensure correct operation before

measurements begin. Following use, the exterior of the instrument should be wiped

down and the entire instrument inspected for any damage, including the lodging of

any insects within the instrument cavity. If the instrument is moved into a heated enclosure

following the measurement period, care should be taken to avoid moisture condensing

in the cavity. Although the transducer coating is not water soluble, over time, chemical

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 Instruments - Diffuse Irradiance, Infrared Irradiance

Each shaded instrument must be checked to ensure that the shading device completely covers

the outer dome of the instrument. These checks are similar to those above for the direct beam

instrum ents.

(10) Data acquisition/computer systems

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 methods to decide whether

the system is operational. Simply looking at a computer screen is NOT sufficient. Tests should

be devised to detect that data are being acquired successfully, that the time stamp is correct

and that the system has not malfunctioned since the last check.

A correct system time is crucial because data are being obtained at one second intervals.

Unfortunately, many PC compatible computers have very poor clock systems. Each day the

clock offset should be recorded and the time corrected if this offset is greater than one second.

If the clock varies by more than 10 seconds per day, a new clock should be installed. A system

changing at a rate of less than one second per month would be ideal (see section 2.3.1).

(11) Where possible, the site operator should be able to review the data from the previous day.

This information will allow him/her to detect any significant changes that may have occurred

during the day. An example of such a change would be a passive tracker that was not level.

During the morning when the observer checks the shading of instruments it would be found

correct, but during the afternoon the diffuse flux would increase because of the shading disk

moving off the sensor.

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