Kipp&Zonen PGS-100 Sun Photometer - Manual (Page 38)

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Instruction Manual - PGS-100 Sun Photometer
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The radiometer of the PGS-100 is temperature controlled at +35 °C ± 2 °C to maintain the wavelength stability and the sensitivity
of the detector in the spectrometer. Therefore, the PGS-100 should normally be continuously switched on to avoid a warm-up
time before the control temperature is reached.
The operating software can be started and stopped with the PGS-100 switched on and connected to the computer. The software
can be started first and then the PGS-100 switched on, but there may be a warm-up time before full accuracy is achieved, as
mentioned above.
Note Turning the PGS-100 off, or disconnecting the ‘PC’ cable, whilst the software is running may cause the hardware
and/or software communication drivers to hang up. In this case it will be necessary to restart the software and
maybe also to restart the computer. Close the software before turning off the PGS-100 or disconnecting the ‘PC’ cable.
5.1 Starting measurement
As mentioned previously the PGS-100 should be already switched on and warmed up.
1. Start the software.
2. In the opening screen, either press the ‘START’ button or wait for the 10 second timer to count down to 0 seconds.
The main screen will appear showing the time to the next measurement. At that time the PGS-100 will make a measurement and
the result will be displayed on the graph as shown below (the example spectrum is for a tungsten-halogen lamp) and stored to
the computer disk. The intensity of the radiation received is given in ‘Counts’. These are arbitrary units, the measured spectrum
shows the relative intensity of the radiation received at different wavelengths.
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A second, small, window opens after each measurement showing the main parameters, including the radiometer internal
temperature and the current cursor position.
The graph can be rescaled to suit the current conditions without affecting the data that is stored. The graph only displays the
last measurement. The red cursor line can be moved using the mouse pointer to any point on the x-axis and the corresponding
wavelength and intensity can be read in the small window.
Each time the radiometer makes a measurement a ‘click’ can be heard. This is the exposure shutter operating, as in a camera.
5.2 Averaging and exposure time
As can be seen in 5.1 step 2, when the light intensity is low and a short exposure time is used (200 ms) with a single measurement
the result can be quite noisy. In the ‘GENERAL’ configuration window the number of ‘shots’ to be averaged can be selected. The
screenshot below shows the effect of averaging 50 shots of 200 ms exposure.
The intensity is not affected, but the noise is significantly reduced. However, when measuring natural sunlight, if too many
averages are made the atmospheric conditions may be changing during the process.
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It is also possible to alter the exposure time. This will, of course allow more light into the spectrometer and increase the
measured intensity and also reduce noise, as shown below.
To stay within the linear range of the detector array, the number of counts should not exceed 10000.
5.3 Measurement time and period
The default Measurement Time will configure as from midnight to midnight each day and with a Measurement Period (interval)
of 1 minute. However, this can be changed in the ‘GENERAL’ configuration window.
Up to six Measurement Times can be set with Start and Stop in hours, minutes and seconds. These must follow in chronological
sequence and must not overlap (allow sufficient time for any averaging of the final measurements to be completed). Each of
these Times can have its own Measurement Period in hours, minutes and seconds and each can be activated or deactivated by
ticking or un-ticking the associated box to the left.
5.4 Waveband selection
By default the ‘WAVE’ configuration window is left empty and the complete spectrum is saved for each measurement. As disk
capacity is not a problem with modern computers it is usually best to use this default setting.
However, it is possible to select up to 20 wavebands and only the data within these bands will be stored. These wavebands must
follow in sequence from short to long wavelengths and must not overlap.
5.5 Log and data files
The data and log files are stored in the installation directory, the default location is c:\Program Files\PGS100_verxxxxxx.
5.5.1 Log file
The pgs100.log file is in text format and lists when measurements were made and when the software was started and stopped.
5.5.2 Measurement data files
The files are identified by date (year, month, day) and format. When there is more than one file for a day there is an extension
number ‘_n’.
It is recommended that these files are backed up regularly.
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An example of a data file for a ‘ONE SHOT’ measurement is shown below, with ’comment’ as the header, the main settings listed,
and the intensity counts at each wavelength. During continuous operation an additional column is created for each measurement.
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5.5.3 Calibration data file
The CD-ROM contains a folder named ‘PGS-100 calibration constant’. In this folder is an excel file containing the calibration
information for the specific PGS-100 radiometer (the serial number is in the file name).
This ‘Calibration Constant’ file gives the sensitivity of the radiometer at each wavelength in the range from just below 350 nm
to just beyond 1050 nm. The sensitivity is in units of W/m²/µm/Count and can be used to convert the ‘counts’ in the measured
data file into the direct solar irradiance in W/m²/µm.
Note There is no software for analysis of the data recorded from the PGS-100 Sun Photometer. It is for the user to
perform data analysis to suit their particular application.
Because of the narrow field of view it is very difficult to calibrate instruments such as the PGS-100 Sun Photometer in a laboratory.
They are best calibrated outdoors against a reference spectro-radiometer, at close to solar noon on a clear day with low aerosol
content in the atmosphere.
A new PGS-100 is calibrated on the roof of the Prede Co. Ltd. Facility in Tokyo, by comparison to a reference PGS-100 which has
been calibrated either at the NOAA Mauna Loa Observatory in Hawaii or at the National Renewable Energy Laboratory (NREL) in
Golden, Colorado.