Chemical Engineering July 2019 - 25

Emerson
Yokogawa
FIGURE 5. The Yokogawa DTSX3000 measures temperature
and distance over the length of an optical
fiber using the Raman scatter principle
FIGURE 4. Emerson's Rosemount X-well uses a
thermal conductivity algorithm and an understanding
of the conductive properties of the temperature
measurement assembly and piping to accurately
measure internal process temperature
for temperature sensors because the
wires inside the sensors are thin, delicate
wires, which tend to break when
you start shaking them too much, "
he says. To combat the problem, the
company developed an RTD sensor
featuring StrongSens technology designed
for high-vibration applications.
" Typical thermocouples can handle
3G of vibration before wires break.
But we've done things with the bonding
method used in the sensor tip
and supported it with wiring so that it
can handle vibration up to 60G, " says
Kiker. " So, if they do have temperature
measurements in an area where
they can't get away from pipe vibration,
StrongSens gives them something
they can use that will be much
more robust, resulting in longer product
life and less downtime. "
And for thermistors used in lower
operating ranges (-40 to 250°C),
there have been advances made in
the oxide powders used to make the
sensors. " Oxides powders were previously
only available in micron sizes,
but now we are able to get them in
nanometers, " says Mehdi Samii, vice
president of engineering with Ametherm
(Carson City, Nev.; www.ametherm.com).
" Why is this important?
The smaller particle size of the oxide
powder makes it easier to produce a
chip or disk that almost reaches theoretical
density. This results in thermistors
that are more rugged, repeatable
and extremely durable. They
can now withstand very drastic thermal
shocks and vibrations without
affecting repeatability, accuracy and
thermal response. This enhances the
product very much. " The company's
line of ACC NTC thermistors is made
with the nanopowders (Figure 3).
Non-intrusive measurements
There are also some applications in
which the material is either too corrosive,
the environment too harsh or the
application too tricky to use traditional
measurement techniques effectively
or efficiently. For these applications,
there are non-intrusive technologies.
" There are times when the process
itself is difficult to measure due
to caustic or abrasive materials or
you may not want to drill into a pipe
and create a potential leak point, but
traditional surface temperature measurement
does not provide an accurate
or repeatable representation of
the internal process temperature, so
we're developing technologies that
don't require penetration, but still provide
accurate measurement of internal
process temperature, " says Kevin
Stultz, global product manager with
Emerson Automation Solutions (Shakopee,
Minn.; www.emerson.com).
Emerson's
Rosemount X-well
technology delivers accurate process
temperature without thermowells
or process penetrations (Figure
4). Using a thermal conductivity algorithm
and with an understanding
of the conductive properties of the
temperature measurement assembly
and piping, this non-instrusive
temperature sensor solution is able
to accurately measure internal process
temperature.
For other applications, such as
those involving reactors or vessels
where hot spots or temperature differentials
can indicate that the product
is not being mixed well or other
issues, it can become cost prohibiCHEMICAL
ENGINEERING WWW.CHEMENGONLINE.COM
JULY 2019
tive to employ traditional single insertion
probes, says Yokogawa's
Meyer. " We offer the DTSX series of
fiber optic sensing cables to provide
continuous temperature sensing for
long distances, " he says. " The solution
provides enhanced visibility into
the process because you can completely
wrap a reactor or a vessel
and program in temperature zones,
which allows users to measure temperature
all along the string. "
The Yokogawa DTSX3000, for
example, measures temperature
and distance over the length of an
optical fiber using the Raman scatter
principle (Figure 5). A pulse of
light launched into an optical fiber
is scattered by fiberglass molecules
as it propagates down the fiber and
exchanges energy with lattice vibrations.
As the light pulse scatters
down the fiber optic cable, it produces
longer wavelength and shorter
wavelength signals, of which both
signals shifted from the launch of the
light source. The intensity ratio of the
two signals components depends on
the temperature at the position where
the Raman scatter is produced.
Temperature is determined by
measuring the respective intensities
of the longer and shorter wavelength
signals. Furthermore, part of the scattered
light, known as the backscatter,
is guided back towards the light
source. The position of the temperature
reading can thus be determined
by measuring the time taken for the
backscatter to return to the source.
No matter what your process, its
environment or your temperature
measurement needs, there is likely
an instrument that can stand up
to the challenges to help bring efficiency,
quality and repeatability to
your process.
n
Joy LePree
25
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Chemical Engineering July 2019

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