72
= pyrgeometer body temperature (K)
= pyrgeometer dome temperature (K)
= the electrical output from the thermopile
= a correction factor for infrared irradiance on unshaded domes.
Details are given in Philipona et al. (1995).
The thermistor temperatures are calculated using the Steinhart and Hart equation with the standard
coefficients provided by the manufacturer:
T = a + b(lnR) + c(lnR)
-1 3
where T = temperature (K)
a,b,c = the standard coefficients provided by the manufacturer
R = the resistance in ohms.
Newer pyrgeometers are now being tested, but have not yet become common in the BSRN network.
The equations provided by the manufacturer of these instruments should be applied to obtain the infrared
flux.
9.3 Quality Assurance Techniques
9.3.1 General testing procedures
9.3.1.1 Redundancy
Having more than one instrument measure the same signal is useful. This provides a means of flagging
a signal as problematic when the redundant measurements differ and gives backup observations during
times when routine maintenance is being done or an instrument is malfunctioning. It is recognized
that having multiple instruments is not always feasible and this is therefore not mandated within the
BSRN framework.
9.3.1.2 Visual inspection
The most rapid means of determining gross problems with the incoming data are visual. It is highly
recommended that the DAS provide near-real-time (minutes) graphical displays of the data, whether
converted to engineering units or simply transducer signals. A preliminary conversion provides the
technician a better appreciation for the data, but large changes such as infinite resistance or zero signal
can be determined easily even from transducer signals. While the data being stored at a one minute
interval provide significant information for later quality assurance testing, the initial displays need only
be the mean values. The more frequent the processed signal is output, the better chance the observer
has of observing unusual phenomena.
On clear days, rapid sampling of the data can provide a graphical means of ascertaining whether individual
instruments are level, or if any biases are in the solar-tracking instruments being used. Such changes
will be obvious through the asymmetry of the data.
Grouping of incoming values is also beneficial. For example, placing the temperature signals of all
of the pyranometers on one graphical display provides a rapid means of determining if one instrument
(or its ventilator) is malfunctioning by showing large temperature departures from the other instruments.
9.3.1.3 Limit Checking
Automatic limit checks can be programmed into many DAS’s. These limits can be such that flags are
automatically inserted into the data stream to warn the operator of potential problems. A key example
is the use of limits to test the resistance of instruments frequently (hourly, daily) and provide a warning
if the resistance is above or below a normal set of limits. Resistance limits of this type can also be
effectively set out with respect to thermistor measurements.
Similar checks can be set up with respect to voltage signals. If instruments have known ranges, limits
can be set to warn the operator if the instruments exceed the range. Two types of ranges must be
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