Temperature Dependency - Kipp & Zonen CM 4 Instruction Manual

1. GENERAL INFORMATION
The thermopile surface is coated with black absorbent paint.
Absorbed radiation is converted into heat which flows through the
thermal resistance of the thermopile to the heat-sink. The
temperature difference (ΔT) across the thermal resistance of the
detector is converted into a voltage.
Most electrical and physical specifications are determined by the
thermopile. The thermopile and the dome determine the spectral
specifications. The optimal geometry of both the glass dome and the
thermopile enables the pyranometer to have a 180° field of view with
good cosine response.

1.2.1 Temperature Dependency

One of the physical principles of a pyranometer is that at a constant
irradiance the detector sensitivity changes with the instrument
temperature. ISO 9060 defines this temperature response as the
percentage deviation due to a change in the ambient temperature
within a specific range of 50 K. The CM 4 temperature dependency
however is specified within an range of 170 K. To keep the
pyranometer performance acceptable the instrument output signal is
electrically compensated. Due to the perfectly balanced
thermoelectric construction the CM 4 temperature dependence is
kept within a deviation of 3%, within the range of -20 °C to 0 °C, 2%
within the range of 0 °C to +100 °C and 3% within the range of +100
°C to +150 °C .
After manufacturing, each instrument is individually checked for its
temperature dependency performance. This is measured in 8 steps
of 25 °C from -25 °C to +150 °C. A typical temperature response of
an electrically compensated CM 4 is given in figure 1.2.
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