Laser Focus World - January 2015

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Opto-Technology

can decrease the response time to po- tential quality issues from days to hours. This depends on the use of autonomous water monitors—ones that need to be compact and cost effective—that con- tinuously test water quality at multiple locations along the network.

Typical causes of changes in water quality include natural events, such as flooding, accidental discharge or spills, or other sources of contamination. UV photometry provides quantitative analysis of the organic content in water. By using continuous spectroscopic measurements instead of intermittent chem- ical testing with grab samples, end users gather process information, detect issues in water quality, and make the necessary process changes in real time.

Traditionally, these water-quality measurements have used xenon flash lamps as the light source for spectrosco- py. Xenon flash lamps provide a broad spectrum of wavelengths and often re- quire an expensive photodiode array for detection. These lamps also require an expensive power supply to maintain lamp performance. Although these high-quality instruments offer precise, accurate measurements of multiple pa- rameters of water quality, they are often more than what a typical water facility requires. The associated costs are also restrictive to small water utilities, and unreasonable for developing regions.

Engineers can achieve the same benefits of xenon flash lamps for a subset of parameters by using UVC LEDs, along with a less costly detector and power supply. Newly available high-performance UVC LEDs offer linearity of measurement that matches the performance of ex- pensive xenon flash lamps. This param- eter refers to the correlation between the optical method of water-quality measurement with a reference method ( typically a chemical measurement in the lab). A more compact, less costly instrument can thus become accessible to a wider cross-section of the market. Additionally, the reduced size and low power consump- tion of these instruments open possibilities for remote monitoring.

Cost analysis of a typical
water-quality monitor

Table 3 provides figures for the typical cost of a broad-spectrum xenon flash- lamp-based monitor versus a wave- length-specific LED version. The UVC LED instrument assumes fixed wavelength detection at two wavelengths: 255 nm for the standard UV254 measurement and a second UV wavelength depending on the water-quality parameter of interest. Operating costs are estimated based on a typical water-qual- ity measurement where the light source would be used for continuous measurement at a duty cycle of 1% ( 1 ms on,

100 ms off).

Cost-effective, compact
instruments for the future

Traditionally, instrument designs that
used UV lamps could take advantage of
the benefits of the lamp, but unavoidably
had to make concessions in instrument
design due to limitations of the light
source. High-performance UVC LEDs
now enable design engineers to address
market pressure for lower-cost prod-
ucts with instruments tailored for ap-
plications in life sciences and environ-
mental monitoring.

By transitioning to UVC LEDs, in- strument manufacturers can reduce instrument costs by 40% to 80%. These cost savings continue at the customer site due to a large reduction in operating and lamp-replacement costs over a five-year period. In addition, these “lite” instrument versions can capitalize on the instant on/off, low power consumption, and high-sensitivity features of UVC LEDs for better performance.