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(iv) the directional responsivity of the instrument (cosine and azimuthal response of the
instrument) for pyranometers
(v) the deviation of the temperature compensation circuit of the instrument over the
temperature range (-10° to +40° of range) or if not compensated, the required temperature
correction of the instrument. In climates where the temperature range is greater than
that specified, instrumentation should be selected to meet the temperature regime.
For the most accurate measurements, the temperature of the thermopile should be
monitored and the signal corrected for temperature variations. A number of instruments
using non-thermopile sensors may be considered if they meet all other criteria.
(vi) the instrument has been radiometrically levelled. That is, the thermopile is horizontal
when the bubble level indicates such (the bubble level should have an accuracy of
±0.1°).
(2) Checks should be made of all wiring to ensure that there are no nicks in the sheathing nor
stress on the connections. The wire should be of a variety that will withstand the clim atic regim e
of the area in which the instrument is to be installed.
(3) All O-rings should be lubricated lightly with a very fine grease (e.g. Dow Corning Model 55
O-ring lubricant or Fischer Scientific Cello-Seal C-601).
(4) All threaded parts should be lubricated in a manner similar to the O-rings.
(5) The thermopile (or the signal transducer) should be visually inspected to ensure that the surface
is uniform in colour and texture.
(6) The BSRN accuracy guide indicates that the case temperature of the instrument should be
monitored. If the instrument is fitted with a thermal measuring device, the wiring should be
checked and the reduction algorithm tested at known temperatures. In the case of pyrgeometers,
all thermistors should be tested.
(7) The inner and outer domes should be checked for scratches or nicks. If found, the domes
should be replaced. In the case of pyrgeometers a similar check should be made of the silicon
dome. However, if the dome requires replacement due to damage, the instrument must be
re-calibrated.
(8) The impedance of the instrument should be checked against the manufacturer’s values.
(9) The desiccant should be fully activated. It is recommended that the desiccating material be
of the bead type (e.g. Trockenperlen, Kali-chemie AG) and not one which easily powders
(e.g. Drierite, Hammond Drierite)
(10) All connectors must be waterproof and should be appropriate for the clim atic conditions in
which the sensor will be deployed. For example, in marine environments care must be taken
against using connectors that are prone to corrode. It is recommended that keyed connectors
be used for greater safety in maintaining instrument polarity.
4.2.2 Mechanical Installation
(1) The instrument should be mounted with the direction of the connector facing poleward for
fixed platforms and away from the solar disk when mounted on solar tracking devices.
(2) The instrument must be fastened to the platform (or ventilating device (see below)) so that
it will not move in inclement weather. The bolts used should be lubricated before assembly
for ease of disassembly. Initially, these bolts (normally two or three depending upon the
instrument) should be not be tightened until the instrument is levelled according to its bubble
level.
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