This invention relates generally to ultraviolet light treatment of fluids and more particularly, to optical sensing and control of ultraviolet light intensity levels in an ultraviolet light fluid treatment process with silicon carbide photodiode detectors.
Ultraviolet (UV) light may be used to sterilize water and other fluids. The ultraviolet light disrupts the DNA of microorganisms in the fluid, which prevents reproduction and thus kills the microorganisms. Regulation of UV light intensity is important in the UV light sterilization process because a minimum level of ultraviolet light intensity is typically required. Also, excessive levels of UV light intensity can result in high maintenance and an associated higher operation cost.
Photodiodes are sometimes used to detect and regulate UV light intensity in such sterilization processes. The UV light spectrum includes wavelengths from 10 to 400 nanometers (nm). However, typical photodiodes used to measure UV light in the known UV light sterilization processes are usually broad range wavelength detectors. For example, silicon detectors are used which are sensitive to light wavelengths ranging from 200 to 1100 nm. Gallium arsenide phosphide and gallium phosphide detectors, which are sensitive to light wavelengths ranging from 200 to 650 nm, are also used. These devices are inherently sensitive to visible and infrared light waves in addition to the UV spectrum. When only UV light detection is desired and outside light sources such as visible light are also present, erroneous signals may result.
Therefore, filters are needed to block out wavelengths longer than 400 nm to eliminate erroneous signals triggered by other light sources. However, filters are prone to degradation which can lead to permitting light outside the UV spectrum into the detector, which results in false and inaccurate readings. Additionally, filter degradation results in costly maintenance and/or equipment downtime.
It would be desirable to provide an ultraviolet light sterilization process incorporating a UV detector that is not sensitive to light outside the UV spectrum to eliminate erroneous signals caused by ambient light sources. It would further be desirable to provide an ultraviolet light sterilization process that does not depend upon light filters thereby lowering maintenance costs and equipment downtime due to filter repair or replacement.