Chemical Engineering March 2014 - 23

American Sensor Technologies
Figure 3. American Sensor Technologies
uses the thickest Hastelloy
diaphragm and a low-operating strain
to create a sensor that offers long-term
pressure measurement
patibility process. O-rings may also
have a limitation in temperature. "
For this reason, he says, there is
performance verification programs
that enable process improvement
initiatives that did not previously
have the means to ensure necessary
measurement quality and trust. "
For example, Endress+Hauser's
FMD71 and FMD72 loop-powered,
4-20-mA HART electronic differential
pressure systems (Figure 2)
eliminate errors from impulse tubing
and provide additional sensor
diagnostics that can be accessed
through an FDT standards-based
tool (like FieldCare), and integrated
and managed in something like
Endress+Hauser's W@M Life Cycle
Management Portal environment.
The FieldCare tool allows access
to the information in an asset management
system via mobile devices,
meaning that from the field, a technician
can call up the calibration
history, diagnostic data, troubleshooting
instruction and other information
needed to properly diagnose
a device problem.
Advanced sensor materials
Another challenge faced by chemical
processors is finding sensors
that can stand up to the corrosive
materials found in the process environment.
Liquid and gas compatibility
and potential contamination
are one of the more difficult issues
they deal with, says Greg Montrose,
marketing manager with American
Sensor Technologies, Inc. (Mt. Olive,
N.J.; www.astsensors.com). " Certain
sensor technologies are limited in
the material that can be used or
the method in which it is sealed, " he
says. " For example, ceramic pressure
sensors are clamped to a metal
process connection with an O-ring
seal. While ceramic has good compatibility
with various liquids and
gases, O-rings need to be selected
carefully and considered in the coma
trend to move toward Hastelloy
C276 sensor material in chemical
processing. " It has a good combination
of media compatibility and
material strength, " says Montrose.
" With the presence of hydrogen sulfide
and chlorides in many chemical
processes, nickel alloys offer higher
survivability than standard stainless
steels. " AST uses the thickest
Hastelloy diaphragm (Figure 3) and
a low-operating strain to create a
sensor that offers longterm pressure
measurement. With the diaphragm
being the thinnest and most critical
piece of a pressure transducer,
a thicker diaphragm ensures it will
withstand a longterm installation.
Using Krystal Bond Technology,
AST designs pressure sensors as a
monolithic piece of material with
no welds, O-rings or fluid fills. Bulk
silicon strain gages are mounted
directly to the top of the metal diaphragm
using a special glass firing
process. With high raw output
signal, inorganic materials and a
thick diaphragm membrane, users
benefit from complete isolation of
the pressure of the fitting and longterm
stability.
According to Endress+Hauser's
McIntyre, ceramic materials are
increasingly finding use in place of
metals in chemical applications. For
example, ceramics that approach the
purity of sapphire are being used in
pressure, differential-pressure and,
now, electronic differential-pressure
sensors to address chemical corrosion,
abrasion, vacuum, shock and
stability challenges in place of traditional
exotic metals and sensor
constructions.
And on the horizon, according
to Bob Karschnia, vice president
of wireless with Emerson Process
Management (Austin, Tex.; www.
emerson.com), is a series of coatings
of nanomaterials that can be used
to help prevent corrosive problems.
" Today we have different materials
like Hastelloy, gold and stainless
steel, depending on the process, but
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Chemical Engineering March 2014

Table of Contents for the Digital Edition of Chemical Engineering March 2014
