test the waters of the Gulf of Mexico
in the wake of the Deepwater Horizon
oil spill.
New Techniques in Practice
With wide applicability, TDLAS is
enjoying great popularity, as entities as disparate as GE Panametrics
and Germany’s national metrology
institute, the Physikalisch-Technische
Bundesanstalt (PTB), exploit its amiable qualities. Chief among the pioneering manufacturers: SpectraSensors Inc., a 1999 spinoff of the NASA/
Caltech Jet Propulsion Laboratory,
and Delta F Corp., the older Massachusetts company that licensed New
Mexico-based Southwest Science’s
patent permitting sub parts-per-billion measurement of contaminants
in semiconductor grade ultra-high-purity gases. SpectraSensors, after its
first sale to El Paso Products, seized
market share from stunned, longtime suppliers to the natural gas
industry, despite the relatively high
price of its new-technology moisture
meters (See Figure 1).
By contrast, CEAS involves a sensor
cell or “cavity” formed with highly
reflective mirrors that allow the laser
beam to bounce back and forth, creating an effective path length on the
order of 50 kilometers. This results in
tremendous sensitivity for detecting
analytes at extremely low levels, generally in the parts-per-billion to parts-per-trillion realm. The catch is that this
method takes considerable technical
know-how to commercialize.
The more widely known CEAS
technology, CRDS, is challenging to
develop, with strong patent protection. As a result, it remains in the custody of the smaller companies that
fostered its development -- chiefly
Tiger Optics LLC, which introduced
the first such commercial analyzer
in 2001 with Continuous Wave
(CW) CRDS, and Picarro Inc., which
launched its ESP-1000 series in 2005
with the technology it calls Wave-length-Scanned ( WS) CRDS.
In the semiconductor market, Tiger
joined Delta F in unseating conven-
tional technologies such as Ametek’s
oscillating crystal moisture analyzer
and MEECO Inc.’s Coulometric-based
technology. Picarro, for its part, made
a strategic decision in 2007 to switch
its focus from the semi market to
greenhouse gas monitoring. In
2010, the company was selected as
a vendor to a global network that
pledges to install 100 sensors to
measure atmospheric greenhouse
gas concentration.
A New Paradigm
Part of what makes these new laser-
based techniques so revolutionary is
the fact that they have toppled the
conventional business model that
has governed instrumentation for
over half a century. For decades,
plant owners needed not only to buy
monitoring equipment, but invariably
paid fees for installation and post-sale
support. Calibration, replacement
parts, consumables, and repairs were
required regardless of the technique,
be it electrolytic, chilled mirror, gas
chromatography, piezoelectric quartz
technology, FTIR or others. Mainte-
nance and operating costs were gen-
erally 50 to 70 percent of the total
long-term cost of ownership. Indeed,
in the late 1990s, DuPont identified
the expenditure on process equip-
ment maintenance in its plants as its
largest controllable expense.
There has to be a Catch
To be fair, the laser-based technologies do have certain notable
limitations. First and foremost, they
are considerably more expensive
than many incumbent techniques.
Also, some are quite bulky, confining
them to fixed installations and applications where space is not at a premium. Exceptions include the sleek
new bright red analyzer from LSE
Monitors, the breadbox-sized HALO
from Tiger Optics (see Figure 2) and
the compact VCSEL laser-based, low
pass oxygen sensor from Oxigraf Inc.,
among others.
