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Product
Technology
How does FCI Thermal Dispersion technology work?
Thermal Dispersion technology uses the principle of measuring the heat
loss, or cooling effect, of a fluid flowing across a heated cylinder. A
typical flow element configuration uses two RTDs, sheathed in
thermowells, separated by a gap. Heat is applied internally to one RTD
relative to the other, creating a differential temperature between the
two. This differential temperature is greatest at no flow conditions and
decreases as flow increases, cooling the heated RTD.
Changes in flow velocity or immersion of the flow element into a liquid
directly affect the extent to which heat is dissipated and, in turn the
magnitude of the temperature differential between the RTDs. This
differential is electronically converted into an electrical signal that
can be used to trip a relay in flow or interface switch applications.
Since the relationship between flow rate and cooling effect is directly
related to mass in gas applications, Thermal Dispersion technology,
combined with advanced signal linearizing circuitry, is used to provide
a highly repeatable and accurate measurement of gas or air mass flow
rates.
Can I safely use FCI thermal flow switches and meters in hazardous
(explosive) gases ?
FCIs Thermal Technology is safe to use in near all flammable and
explosive liquids and gases. Most of the products that FCI offers have
independent agency approvals such as, Factory Mutual, Canadian Standards
Association and CENELEC for use in hazardous locations.
Typical ratings are Class I and II, Groups B, C, D, E, F, and G,
Division 1 and 2, EEx d LLC T4. Group B gases includes hydrogen. In
addition to using special explosion proof enclosures for these hazardous
areas, the circuitry is designed so that the maximum skin temperature of
the flow element never nears the ignition temperature of the gas or
vapor. Verification of the maximum surface temperature, known as
T-rating, as well as other requirements for safe use of the instrument
in hazardous locations are carefully evaluated by the independent
testing agencies before issuing their approval. Refer to FCI Tech Brief
TB001 for a comprehensive discussion on understanding instrumentation
T-ratings.
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Flow and Level Switches
Where are FCI thermal dispersion flow switches used?
FCI thermal dispersion flow switches are used in all industries and in
varying applications. Chemical/Refinery, Oil and Gas, Nuclear and Fossil
Power, Food, Pharmaceutical, Steel, Aerospace and many other industries
routinely utilize FCI flow switches. Their popularity is a result of
years of reliable service in some of the most challenging process
applications.
FCI flow switches are used to protect very costly devices and processes
as well as monitor emergency flow conditions. Pumps, motors and fans
require a reliable safety device to prevent damage and extensive down
time in the event of a flow blockage or product depletion. Other common
applications include chemical additive or chemical feed monitoring and
flow verification to an analyzer. A reliable flow switch is mandatory to
assure continuous process monitoring.
I am specifying flow switches for pump protection. There appears to
be a wide price difference between mechanical type flow switches and FCI
thermal dispersion type flow switches. Why should I select FCI's thermal
dispersion type product ?
Mechanical switches are susceptible to breaking, sticking, coating,
false trips, no trips and orientation problems. They are often ignored
or taken out of service negating any benefit they were initially
intended to provide.
Thermal flow switches, on the other hand, have no moving parts, are
not susceptible to contamination, can be oriented in any pipe
configuration, are manufactured out of any compatible material and can
handle high temperature and high pressure. FCI thermal flow switches are
not contaminating, can be supplied fail-safe, and are extremely
reliable.
A mechanical flow switch can be in service for months before the effects
of the process take its toll. What works the first month, does, not
necessarily continue to work into the future. Over time, parts wear and
material can build up. This is not a problem that effects the FCI
thermal switch. No moving parts, no sticking, no weak points to break,
no possible contamination to the process from worn or broken pieces.
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How do I select a gas flow meter that will provide the performance I
need for my application?
Match your application to the appropriate measurement technology.
Accurate flow measurement starts with selecting the best flow meter
technology for your application. Every application has a set of
requirements that narrows the choice of technologies. For example,
thermal dispersion might work best in a dirty process gas, like biogas,
be-cause this technology provides no-moving-parts reliability, direct
mass flow measurement, and wide range ability. However, positive
displacement might be the best technology choice for the custody
transfer of natural gas.
An Instrument Specification Sheet is a good place to find information
that will help select the most appropriate flow meter technology for an
application. This sheet identifies the application's process temperature
and pressure, gas composition, piping configuration, accuracy
requirements, and more. Narrow your technology search by matching the
application information against the suggestions shown in the
accompanying Gas Flow meter Selection Chart.
Now forward your application information to vendors that offer the most
appropriate flow meter technology. Be sure to include as much
information about the application as possible and highlight your
realistic performance expectations. Do not request 0.5 percent accuracy
if the application needs only 5 percent accuracy. Ask these vendors to
evaluate your application and provide a product recommendation. Use the
information you receive to revise your specification (if necessary),
finalize your preferred vendor list, and prepare your request-for-quote.
What can be done if I can't meet the flow meter's recommended
installation requirements?
Use a flow conditioner. Flow meter manufacturers usually provide
"recommended installation" instructions with their products. These
instructions specify the minimum amount of straight, unobstructed pipe
that should be located upstream and downstream of the flow meter. It's
often not possible to provide this required straight pipe due to space
constraints and economic demands. Consequently, flow meter accuracy
suffers as a direct result of an inadequate amount of straight pipe. If
high flow meter accuracy is demanded, even with inadequate straight
pipe, a flow conditioner should be used. There are many types of flow
conditioners available (vanes, tube bundles, perforated plates);
however, the new Vortab flow conditioner offers several advantages. The
Vortab's unique tab design (see sketch) provides excellent isolation
from disturbances, little pressure loss, and immunity to fouling.
I need to accurately measure gas flow in a very large duct. What type
of mass flow meter should I specify ?
Specify a multipoint, insertion flow element. Single-point, insertion
flow meters are a sensible choice when flow rate measurements must be
made in large size pipes or ducts. However, because gross flow velocity
profile distortions are likely in very large ducts, a single-point flow
meter cannot accurately measure these highly skewed flow conditions (see
sketch). Selecting a technology that allows for the averaging of
multiple measurements provides a reasonable solution to this problem.
When making multipoint air or gas flow measurements in large ducts,
thermal dispersion technology offers significant benefits that place it
far ahead of the other technologies. Thermal technology offers direct
mass flow measurement (without separate temperature, pressure, or
density measurement), fouling immunity, low flow sensitivity, and wide
rangeability.
Why isn't this mass flow meter indicating flow rate, temperature or
totalization correctly ?
Check the flow meter's functionality, specification, installation, and
validate the comparison standard. If you suspect that your newly
installed flow meter isn't indicating correctly, start your
troubleshooting procedure with a flow meter functionality test, but
don't stop there. Review your application parameters against the Gas
Flow Meter Selection Chart and seek advice from the product vendor if
your flow meter appears to have been incorrectly specified. Next,
confirm that the flow meter has been installed per the manufacturer's
installation guidelines. Finally, check the measurement method or
calculation that was used as the reference or comparison standard. Many
"reference" methods are, at best, estimates (generic blower curves,
valve positions, operator experience, stoichiometric calculations). As a
last resort, make zero and span adjustments.
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Flow Conditioners
What can be done if I cannot meet the mass flow meter's recommended
installation requirements?
Use a flow conditioner. Flow meter manufacturers usually provide
"recommended installation" instructions with their products. These
instructions specify the minimum amount of straight, unobstructed pipe
that should be located upstream and downstream of the flow meter. It's
often not possible to provide this required straight pipe due to space
constraints and economic demands. Consequently, flow meter accuracy
suffers as a direct result of an inadequate amount of straight pipe. If
high flow meter accuracy is demanded, even with inadequate straight
pipe, a flow conditioner should be used. There are many types of flow
conditioners available (vanes, tube bundles, perforated plates);
however, the new Vortab flow conditioner offers several advantages. The
Vortab's unique tab design (see sketch) provides excellent isolation
from disturbances, little pressure loss, and immunity to fouling.
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