User guide

8
2 OPERATION
2.1 Measurement of direct solar radiation
After completing the installation the pyrheliometer will be ready for operation.
The irradiance value (E↓Solar) can be simply calculated by dividing the output signal (Uemf) of the pyrheliometer by
its sensitivity (Sensitivity) as shown in Equation 1. For calculation of the direct solar irradiance the following formula
must be applied:
S
U
E
emf
rDirectSola
=
Equation 1: Calculation of solar radiation
Where:
E
DirectSolar
= Solar radiation [W/m
2
]
U
emf
= Output of radiometer [μV]
S = Sensitivity of radiometer [μV/W/m
2
]
To be certain that the quality of the data is of a high standard, care must be taken with daily maintenance of the
radiometer. Once a voltage measurement is taken, nothing can be done to retrospectively improve the quality of
that measurement.
2.2 Measurement of instrument temperature
Inside the detector assembly a Pt-100 (Class A) and 10kΩ thermistor are placed to provide the detector temperature.
The location of these temperature sensors is shown in Figure 2.
Detector assembly
10k Thermistor
Pt-100
Detector
Figure 2: Position of temperature sensors inside the CHP 1 detector assembly
The temperature of the Pt-100 and 10kΩ thermistor can be derived using Equation 2 and Equation 3
T =
Temperature
T [ ”C ] = ResistanceR =
T =
- R
100
+ 1
Equation 2: Temperature vs Thermistor Resistance Equation 3: Temperature vs Pt-100 resistance