Brewer stability checks with the new UV Stability Kit
The Ozone measurement by the Brewer is ratiometric in nature. However, to correctly report UVA, UVB and UVE irradiances in W/m2 the ‘absolute’ ultraviolet spectral response must be known. A UV calibration is carried out in Delft, or on-site, using a very precise calibration system, but regular field checks should be carried out to check that the response is stable.
It is normal practice to check the Brewer Spectrophotometer response with an external UV Stability Kit once every two weeks. It is also advisable to do this before and after relocating a Brewer.
In our Newsletter 32, you can find the introduction of our new and much improved UV Stability Kit, and you can find more detailed information following this link: http://kippzonen-brewer.com/news/new-uv-stability-kit-brewer/
This summer the Brewer team from Kipp & Zonen participated in the Regional Brewer Calibration Center-Europe (RBBC-E) intercomparison at Huelva, Spain. You can find a report at http://kippzonen-brewer.com/news/the-2015-brewer-intercomparison-at-el-arenosillo-spain/
As Kipp & Zonen is located in Delft, the Netherlands, we drove our two reference Brewers, #158 and #230 almost 2300 km by car. It is a pretty long distance to cover and it is very important to have stable and reliable instruments when they arrive at the intercomparison site.
A set of UV spectral response scans was made when Brewer #230 was installed at the intercomparison in Huelva, using the new UV Stability Kit (with lamp no. KS079). A further set of scans was made after the Brewer was returned to Delft. The results are shown in Fig.1.
You can see that the absolute deviations between the scans are very small and demonstrate that Brewer #230 is stable during transport.
Fig. 2 shows the relative difference between the reference scans in Spain and those made after reinstallation at the factory. The higher counts in Huelva can be explained by the higher ambient temperature in Spain compared to the Netherlands.
As an example for demonstration we used one lamp, number KS079. However, the UV Stability Kit contains three calibrated 200 W quartz halogen lamps and it is recommended to scan all of them each time, to check the absolute and relative agreement between them.
It is important to track the stability of your Brewer to be sure that it can make accurate ultraviolet measurements until the next intercomparison or recalibration.
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