August 5, 2009--In yet another example of how far vertical-cavity surface-emitting laser (VCSEL) technology has moved from its telecom origins, Applied Analytics Inc. (AAI; Concord, MA) is introducing what it calls "an industry-proven and cost-effective solution for oxygen-monitoring needs": the TDL-506. The system is intended to produce accurate, fast, and stable oxygen measurements in even the most volatile process streams, says AAI.
The TDL-506 is named for the tunable diode laser at its core. The ability to emit high-intensity light at an extremely specific wavelength is critical for monitoring the sharp, isolated absorbance peaks that are characteristic of diatomic oxygen. The VCSEL housed in the TDL-506 provides this ability; the system is constructed specifically to monitor the R-branch of the oxygen A-band at 760 nm, minimizing interference and optimizing detection resolution.
The VCSEL's manufacturing costs are low, and the units can be tested at the mid-production wafer level. Although VCSEL technology was developed primarily with projects such as Gigabit Ethernet and commercial photonics in mind, AAI engineering has deployed the VCSEL for process monitoring in the form of the TDL-506. The analyzer was built to fulfill the performance specifications for oxygen-sensing applications at a price point lower than for a system constructed around the older, industrially entrenched distributed-feedback (DFB) lasers.
Close-coupled sampling
The TDL-506 is close-coupled to a chimney and measures directly on the stack. The probe draws a continuous sample from the process stream into the flow cell via a membrane that filters out interfering particles. Unlike cross-spec analyzers that measure across the pipeline, the TDL-506 can be regularly zeroed to ensure accurate concentration readings over the long term. The TDL-506 also steers clear of the pitfalls of extraction sampling, where the sample is dried, cleaned, and inevitably diluted before measurement.
