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Watertight Spectrometer Relies on Cool Light

Photonics Spectra
Oct 2000
Daniel C. McCarthy

Not long ago, BASF AG used a benchtop spectrometer and a cuvette to ensure that certain chemicals being shipped from its plant in Ludwigshafen, Germany, were free of impurities. The task detained the shipment a few hours and left the potential for human error, but it was the best way for BASF to ensure itself and its customers that it delivered a clean product. Now a compact in-line spectrometer from tec5 AG is delivering the same assurances with greater speed and accuracy.

Altogether, the light source, two spectrometers and control electronics comprising the instrument measure about 30 × 20 × 30 cm. From this, a fiber optic probe extends into the flow stream and collimates the light through a quartz tip. Made by Hellma GmbH & Co. in Mülheim, Germany, the probe incorporates no cement or glue in its optics, which enables a higher optical throughput and makes it more resistant to solvents.


The components inside tec5 AG's in-line spectrometer fit into a 30 × 20 × 30-cm housing, excluding the probe. A low-power deuterium-tungsten lamp minimizes heat within the watertight housing but emits enough light to allow the probe to test within a second. Courtesy of tec5 AG.


A watertight housing protects the other components from the chemical flow stream. But this required tec5 to integrate a low-power light source to reduce the amount of heat. "If you create a lot of heat, you need complex, expensive dissipation methods," explained Gert Noll, tec5's director of marketing and product management.

Most light sources for this type of application are based on deuterium and require 30 W to operate, but tec5 found its solution in a deuteriumtungsten hybrid lamp from Heraeus Noblelight GmbH in Hanau, Germany. The source requires only 6 W to emit enough light to allow the probe to test within a second.

The detection mechanism is a two-channel system integrating two spectrometers from Carl Zeiss Jena GmbH in Germany. One sensor scans the flow stream for impurities, while the other monitors the light source to act as a reference. "Light sources always have slight fluctuations," Noll said.

An electronic multiplexer measures both channels simultaneously and enables BASF to handle the instrument from a central control station up to 100 m away without sophisticated cabling. The instrument measures transmission of the light between 210 and 400 nm. Obtaining information below 220 nm is difficult because of effects in the fiber. The system's sensitivity can detect trace elements as low as 10-4, Noll said. 

This type of application also can use attenuated total reflection probes, noted Camiel Heffels, a development engineer at BASF. But that technology is better suited to strongly absorbing substances such as dyes. Because the chemical monitored by tec5's instrument is clear, transmission spectroscopy is required. One challenge, however, remains for BASF's application. The instrument from tec5 cannot detect very small quantities of suspended contaminants. "We're still looking for that solution," said Heffels.


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