New UV Stability Kit for the Brewer
For measurement of Ozone, Sulphur Dioxide and Aerosol Optical Depth the absolute value of the irradiance measured by the Brewer Spectrophotometer is not particularly important. If there are sufficient photons reaching the photo-multiplier tube (PMT) detector to produce an acceptable signal-to-noise ratio, it is the ratios of the signals at each of the six slit mask wavelengths that are used to calculate the values. However, for ultraviolet measurements of UVA, UVB and UVE irradiances the absolute sensitivity is critical and this must be periodically calibrated.
Normally, this is done indoors at the factory or during a site visit using a NIST-traceable spectrally calibrated 1000 W quartz halogen lamp. This is mounted at a critical distance from the Brewer input optics in a specific orientation, ventilated, and driven by a very precise, stabilised power supply.
It is necessary to periodically check that the Brewer UV response is stable with time and for many years; there has been a small, portable ‘UV-B Stability Kit’ available that uses 50 W quartz halogen lamps. However, the small lamp housing is mounted directly over the Brewer dome and cannot isolate the lamp well from the environment, so it is affected by wind cooling and temperature changes. In addition, the power supply is relatively unsophisticated and there is variability between lamps when newly calibrated of 2-3%. Compared to the factory calibration, it is difficult with this kit to get closer than ± 5 % for an outdoor UV response check.
We are now supplying as an accessory for Brewers a new UV Stability Kit and Precision Power Supply with much better performance. This kit is supplied with three pre-aged and calibrated 200 W quartz halogen lamps that have little variation. The lamp housing is better protected environmentally and the lamp filament is at a similar distance and same effective aperture as the 1000 W factory setup.
A specially designed very stable, temperature compensated, AC-DC power supply is used to drive the lamp and a ventilation fan in the lamp housing. A keyboard and liquid crystal display (LCD) enable setting and display of output current and voltage, ramp time, cooling time and status.
Compared to the factory indoor 1000 W lamp calibration, it is possible with this new kit to obtain results within 1-2 % for an outdoor UV response check in reasonably stable weather conditions.
The part number of the new UV Stability Kit and Precision Power Supply is 3315001 and the price is the same as the original BA-C126 UV-B Stability Kit, which is now no longer available.
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