Campbell Scientific CHP1 Pyrheliometer (from Kipp & Zonen) - Manual (Page 11)

11
5 PYRHELIOMETER PHYSICAL PROPERTIES
In this chapter the principal physical characteristics of the CHP 1 pyrheliometer are given.
5.1 Spectral range
The spectrum of the solar radiation reaching the Earth’s surface is in the wavelength range between 280 nm and
4000 nm, extending from ultraviolet (UV) to the far infrared (FIR) as shown in Figure 9. Due to the excellent physical
properties of the quartz window and black absorber paint, the Kipp & Zonen CHP 1 pyrheliometer is equally
sensitive in a wide spectral range. 97-98 % of the total energy will be absorbed by the thermal detector.
0
0.2
0.4
0.6
0.8
1
200 700 1200 1700 2200 2700 3200 3700
Wavelength [nm]
T
ran
sm
it
tan
ce [A
rb
it
ra
ry u
n
its
]
Typical
window
Typical Solar
spectrum
Figure 3: Solar irradiance spectrum at the Earth’s surface and pyrheliometer response
5.2 Sensitivity
The radiometer thermopile sensitivity is mainly determined by the physical properties of the detector itself. The
thermoelectric power, thermal conductivity of the junctions and the overall dimensions of the sensing element are
related to its sensitivity.
5.3 Impedance
The radiometer impedance is defined as the total electrical impedance at the radiometer output connector fitted to
the housing. It arises from the electrical resistance in the thermal junctions, wires and passive electronics within the
radiometer.
5.4 Response time
Any measuring device requires a certain time to react to a change in the parameter being measured. The radiometer
requires time to respond to change in the incident radiation. The response time is normally quoted as the time for
the output to reach 95 % (sometimes 63 %) of the final value following a step-change in irradiance. It is determined
by the physical properties of the thermopile and the radiometer construction. The CHP 1 has a fast response, which
makes them suitable for measuring solar radiation under variable weather conditions.
5.5 Operating temperature
The operating temperature range of the radiometer is determined by the physical properties of the individual parts.
Within the specified temperature range Kipp & Zonen radiometers can be operated safely. Outside this temperature
range special precautions should be taken to prevent any physical damage or performance loss of the radiometer.
Please contact your distributor for further information regarding operation in unusually harsh temperature
conditions.