Chemical Engineering December 2010 - 19

Endress+Hauser
Newsfront
On the LeveL
A
Level measurement technology was lacking in the
past, but new technologies are increasing reliability
and overcoming traditional measurement obstacles
s level is a critical parameter for
those in the chemical process
industries (CPI), level measurement
instrumentation has been
around for some time. But as processors
scramble to become more efficient,
reduce waste, control inventory and
abide by environmental regulations,
level measurement has become even
more important. As a result, device
manufacturers are improving existing
technologies with value-added characteristics,
such as increased accuracy,
better electronics, reduced maintenance,
data-management capabilities
and other advancements that allow
processors to apply reliable level measurement
to their toughest and most
critical applications with confidence.
Level measurement plays a variety
of roles in the CPI from measuring inventory
levels to ensuring consistency
during the production process to preventing
pumps from running dry and
tanks from overflowing. And there are
as many different devices and technologies
available as there are applications.
But if you look closely at level
measurement through the years, it's
easy to see there was an opportunity to
improve just about every type of technology
or to switch to a newer technology
to better solve existing problems,
says Will Bailey, strategic business
manager with Omhart Vega (Cincinnati,
Ohio). " Some of the more antiquated
technologies out there really
needed improvement regarding the
amount of maintenance they required.
By switching to a newer technology
or improved device that is more reliable
and requires less maintenance,
it provides a host of opportunities for
processors to improve their processes,
products and safety records, " he says.
Historically it was not uncommon
to use differential pressure technologies
or displacers, such as mechanical
floats, in level measurement applications.
However, these technologies
often had issues with changes to the
specific gravity of a product, so there
would be inaccuracies. To offset this,
technicians had to recalibrate the devices
for each new material or product,
but with some of the newer, improved
technologies, this step is not necessary.
This reduces maintenance activity
and improves the process.
Many older types of level measurement
devices, such as displacers, required
frequent mechanical checks
and, just as often, removal from the
process for cleaning. " Many of the
available technologies no longer require
that type of maintenance, so
we're seeing a big push in the industry
to move toward lower maintenance,
higher accuracy technologies, " says
Bailey. " It simply and easily removes
the challenges people historically dealt
with regarding level measurement. "
Radar to the rescue
Free-wave radar and guided-wave
radar seem to be taking the industry
by storm in recent years, and with
good reason. Radar solves the problems
mentioned above in a host of
processes that have been traditionally
difficult to deal with.
Radar devices can accurately handle
specific gravity change, changes in
capacitance or conductivity and there
are few or no moving parts. The technology
is also impervious to humidity
and foams.
As a general rule of thumb - though
it varies from application to application
- guided-wave radar, which features
Figure 1.
As a multiparameter
technology
that provides
interface and level
measurement
in liquids, the
FMP55 combines
guided radar and
capacitance technologies
in the
same unit on the
same rod or cable
an antenna line or cable that goes into
the vessel containing the product to
be measured and a radar signal that
travels up and down that line, is used
on the process control side. Free wave,
which is a non-contacting form of microwave
level measurement, is more
likely to be used in finished products
for inventory control in both liquids
and solids.
Not only is the ability to measure
both liquids and solids a bonus, but
radar technologies also offer improvements
in signal reliability, which helps
with traditionally difficult interface
applications (where there is an emulsion
layer between two materials that
have separated in the storage or process
vessel), or where vapors or dust
are an issue.
ChemiCal engineering www.Che.Com DeCember 2010 19
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Chemical Engineering December 2010

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