Campbell NR-Lite, Instruction Manual

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NR-LITE Net Radiometer
2
1.1 Electrical Properties
The thermopile consists of a number of thermocouples connected in series,
essentially providing a highly sensitive differential temperature sensor. The
thermopile generates a voltage output – the sensor itself is passive, and so no
power supply is required.
The upwards and downwards facing sensor surfaces are connected to the upper
and lower thermopile junctions respectively, and so the sensor can measure the
differential temperature. This temperature differential can be measured to a
high accuracy (in the order of 0.001 degrees), and is proportional to the net
radiation.
The thermopile determines the electrical characteristics of the instrument. Both
upper and lower facing sensors have a field of view of 180 degrees, and their
angular characteristics conform closely to the so-called ‘cosine’ response (see
following sections).
The electrical sensitivity for the thermopile changes with temperature, and no
nominal sensitivity value is available.
FIGURE 2. Electrical Circuit for the NR-LITE Net Radiometer
1.2 Spectral Properties
The spectral properties of the NR-LITE are determined by the Teflon surface
of the sensors. An approximate spectral sensitivity response curve for the
instrument combined with the spectrum of the sun under a clear sky, and the
spectrum of outgoing far infra-red radiation (F.I.R.) is shown in Figure 3,
below.