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FCI FAQ Library

FCI FAQ Library

Frequently Asked Questions

FCI's FAQ Library provides immediate answers to the most frequently asked questions about FCI products, their applications and installations.

If you have a new question that is not listed in our archive or you would like to discuss the specific requirements for your application, please contact us at 800-854-1993 (toll free within USA), or 760-744-6950

The FAQ library is organized by:

Product Technology
Flow and Level Switches
Mass Flow Meters
Flow Conditioners

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 a flow, level or interface switch applications, or which can be linearized across a large turndown to provide a wide range air/gas mass flow meter.

Can I safely use FCI thermal flow switches and meters in hazardous (explosive) gases ?

FCIs Thermal Technology is safe to use near and in flammable and explosive liquids and gases. Many of FCI products global agency approvals for installation in Ex type environments. These FCI products have been independently tested and certified by these agencies. Further, FCI approvals are on the full instrument, not just an enclosure rating. FCI products carry Ex approval ratings to FM, FMc, CSA, ATEX, IECEx, Inmetro, EAC TR/CU, NEPSI, CCoE and others.

Many products carry ratings that Class 1, Div.1, Zone 1 ratings. In addition to using special explosion proof enclosures, 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 can be found where ever liquids, air or gases are present in the process or plant operations. From water to oils and from air to hydrocarbon gases you will find FCI flow and level switches in operation. Chemical plants, refineries, oil and gas extraction and treatment, nuclear and fossil power plants, water and wastewater treatment, mining, food and beverage, and even on-board aircraft and ships.

FCI flow switches are often used to protect expensive processes and devices, as well as monitor emergency flow conditions. Pumps are monitored for a low, no or high flow conditions to prevent pump damage and costly repairs. Chemical additive feed lines are monitored to ensure and verify the fluid has been properly injected. Similarly, the flow steam into sampling systems and analyzers can be verified to ensure an effective sample has been provided.

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.

FCI 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 fluid compatible material and can handle high temperature and high pressure. FCI thermal flow switches are not contaminating and there are no orifices to trap fluid or become clogged. FCI flow switches have reliability pedigrees such as SIL ratings, MTBF ratings in excess of 190 years and warranty claims of less than 0.03%!

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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Mass Flow Meters

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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