UVB-1/UVA-1 Frequently Asked Questions
4. Instrument Selection
UV-A radiation refers to atmospheric radiation from 320 nm-400 nm (that's 0.320-0.400 m m). UV-A is very important to photosynthesis and plant studies.
UV-B is the shortest wavelength atmospheric radiation that actually reaches the ground, and covers from 280-320 nm (that's 0.280-0.320 nm). However, it is UV-B that causes skin cancer over prolonged exposure. Due to the strong absorption of UV-B by ozone, the actual amount of UV-B reaching the ground is highly seasonal and depends on the solar zenith angle. With a high enough resolution instrument, the UV-B spectrum will be seen to be highly variable, i.e., it is characterized by spikes and troughs instead of being a smooth curve. This spectral structure of the sun's radiation arises from atomic absorption within the sun's approximately 6000° K photosphere. Instruments exist both to measure the total integrated broadband radiation (e.g. the YES UVB-1), as well as to measure radiation along narrow wavelengths (e.g. high resolution narrowband sensors like the YES UVMFR-7 or UVRSS).
UV-C is "extraterrestrial" solar radiation, and includes light with wavelengths between 100-280 nm. Thankfully for all of us living on earth, UV-C is fully absorbed by stratospheric ozone. In fact, UV-C is a major factor in the continuous creation of ozone in the upper stratosphere. UV-C is also called "hard UV" or "vacuum ultraviolet" in certain disciplines and is useful in many industrial processes and bacteriological applications.
2. Can you compare the UVB-1 instrument with the Blue Wave BW-100 radiometer from Vital Technologies Corp. or other broadband UV radiometers?
Vital went out of business in 1997. The BW-100 and their other broadband instruments used thin film interference filters instead of phosphors and were therefore not as stable as most UV-B users require. In contrast, in 1993, our model UVB-1 was evaluated by NIST's radiometric physics division along with other manufacturers' instruments. Based on the outcome of these NIST tests, the US government selected YES UVB-1 instruments for the UV monitoring network run by the U.S. Department of Agriculture. For more information, visit the USDA UV-B monitoring program at http://uvb.nrel.colostate.edu.
The two instruments are identical, except that the UVA-1 pyranometer has a spectral response of 320-400 nm and features a detector that uses a phosphor system responsive to UV-A.
Yes, the output for a UVB-1 or UVA-1 pyranometer is an analog 0-4Vdc signal…so any data logger than can digitize the signal in this voltage range will work. Be sure that the data logger has differential input channels. (If it does not state so, it is likely single-ended as these are less expensive to manufacture). You must use differential inputs to eliminate analog ground loops. Also, some data loggers have input range limitations that can be easily accommodated. For example, the popular Campbell Scientific model CR-10 data logger has only a maximum input range of ± 2.5Vdc. In this case you need to simply use a two-resistor voltage divider (10kW ) to step down the voltage by a factor of 50%. Finally, do not forget that you need a source of positive and negative electrically quiet DC as well, which most data loggers do not provide. A dual output DC supply, such as the UVPS-1 will also be needed.
5. Does operating two pyranometers such as the UVB-1 and UVA-1 require two separate UVPS-1 power supplies?
No, one UVPS-1 power supply will run two pyranometers: each UVB-1 or UVA-1 needs 500mA@+12V ea, plus about 30mA@-12V ea. You can also use our YESDAS-2 data logger to provide DC from your AC power mains. If you are technical, you can even build your own DC supply (however, it must be an electrically quiet linear-type DC power supply, not a switching-supply).
In the April 1998 issue of the Bulletin of the American Meteorological Society a peer-reviewed paper describes the calibration stability of the US government's UV monitoring network over a four year period. This paper describes the long term calibration stability of approximately fifty YES model UVB-1, MFR-7, and UVMFR-7 instruments during a four year period, and concludes that the stability has been outstanding.
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