The Advanced Technology Behind Air Monitor Flow Measurement Products

Air Monitor products are used for measuring clean airflow, dirty airflow, and combustion airflow in refineries, foundries, aerospace, power, electronics manufacturing, food & beverage, pharmaceutical, automotive, chemical, wastewater, pulp & paper, and environmental industries. Air Monitor uses multi point averaging pitot tube technology coupled with ultra low, high accuracy, differential pressure measurement to measure air flow in any industrial environment.

Pitot Averaging Technology

The Air Monitor multi-point self-averaging pitot averaging technology is unique in that it is a pure instrument measuring true velocity pressure (total pressure – true static pressure). Other technologies measure a reference pressure on the back or side of the probe resulting in a DP that is not true velocity pressure as derived from Bernoulli’s Equation. This reference pressure requires the use of correction factors that vary with Reynolds number (i.e. velocity and density changes) in order to relate the measured DP to true velocity pressure. The Air Monitor system also utilizes the Fechheimer method of true static pressure measurement along with a chamfered impact or total pressure measurement to provide an accurate velocity pressure measurement and do so with pitch and yaw angles up to ± 30 degrees without requiring additional corrections.

Differential Pressure Technology

Differential Pressure technology is commonly used to measure fluid velocity due to their well-defined relationship. The square root of the differential pressure is proportional to the velocity of the fluid. In ducted systems the total pressure consists of the velocity pressure and static pressure. By measuring the total and static pressures in a duct, the velocity pressure can be obtained by subtracting static pressure from total pressure. This is achieved in practice by directly measuring the differential pressure between the two.

Air flow measurement over a large velocity range requires an extensive selection of DP transducers with multiple upper range limits (URLs) to fit the required application - from ultra low range like 0.05” w.c. URL transducer and higher. Air monitor offers this ultra low range DP sensing capability coupled with the Auto-zero function to provide a highly accurate DP measurement with long term calibration stability starting for 0.05” w.c. URL transmitters.

For more information in Northern California and Northwestern Nevada, contact CTi Controltech by calling 925-208-4250 of visit their web site at https://cti-ct.com.

Flowmeter Basic Considerations

This multivariable vortex flowmeter provides output
of temperature, pressure and flow.
Image courtesy Azbil N.A.

Flow measurement, the quantifying of a point passage rate for gasses and liquids, is used throughout process applications in power generation, chemical manufacturing, petrochemicals, pulp and paper, water and wastewater, bio-science, semiconductor and many other manufacturing processes. There are two measurements of fluid flow in use: volumetric and weight or mass.

Flowmeters are used to measure the rate or quantity of fluid flow in an open or closed system. They are frequently found installed on piping systems, though there are also instruments capable of measuring liquid flow in open channels. The various measurement technologies have differing installation criteria, with some requiring placement of a sensing element in the flow path, others merely in contact with the flow medium, and still others with no media contact needed at all.

Flow measuring devices can be categorized in a few ways:

• Inferential Types: Such as variable area flowmeters (rotameters), target flow meters and turbine flow meters.
• Electrical Flow Meters: Such as electromagnetic flow meters, ultrasonic flowmeters and laser doppler anemometers.
• Mechanical Type: Such as orifice plates, venturi tubes, flow nozzles, pitot tubes, positive displacement meters and mass flow meters.
• Other: Such as vortex shedding flow meters, Coriolis, cross-correlation flowmeters, purge flow regulators, flow meters for solids flow measurement and flow switches.

Flow measurement instruments can be integrated into existing fluid transfer systems or installed on new lines, either inline or via insertion. Inline flowmeters mount in the piping system using downstream and upstream connections. Immersion flowmeters use a probe or sensor penetrating the piping, positioning the sensor in the flow stream.

For best results, it is important to heed manufacturer recommendations for installation. There are various flow characteristics that may have an adverse impact on measurement accuracy. Providing flow conditioning structures or maintaining minimum required straight runs on the upstream and downstream piping may be a requirement for some instruments. Each measurement technology will have installation recommendations and limitations.

For proper selection criteria, you should always know the physical state of the process media (solid, liquid, gas, steam), the condition of the media (clean, dirty, viscous, corrosive, flammable), piping size and range of flow rate. The process pressure and temperature can have an impact, as well.

Share your flow measurement challenges with a process measurement specialist and leverage your own knowledge and experience with their product application expertise to develop an effective solution.

Multivariable Vortex Flowmeter from CTi Controltech

Vortex Flowmeters

This vortex flowmeter combines, volumetric flow,
temperature and pressure measurement into a single instrument.
Image courtesy Azbil, N.A.

Vortex shedding flowmeters provide consistent process fluid flow rate measurements across a wide range of applications. These flowmeters measure the volumetric flow rate of steam, gas, and low viscosity liquids, boasting both versatility and dependability when used in conjunction with process control systems.

Vortex shedding refers to the phenomenon wherein flowing gas or liquid forms vortices around a solid obstruction placed in the flow path. The measurement technology returns an indication of the process fluid velocity, which can then be used with other data to calculate volumetric or mass flow. Vortex technology is well suited for many applications involving cryogenic liquids, hydrocarbons, air, and industrial gases. Vortex flow measurement does require contact between portions of the measurement instrument and the process media, so these flowmeters are commonly fashioned from a range of corrosion resistant materials. Compatability between the instrument construction materials and process media must be considered for every application.

The process of measuring the flow involves both the flowmeter and the ability for other instrumentation to measure the vortices themselves in order to calculate velocity. Ultrasonic sensors have become popular tools for measuring vortices. Applications involving flow measurement of high viscosity fluids are not well suited for vortex technology because extremely viscous fluids do not behave in the same manner as lower viscosity fluids when their flow path is obstructed. Splitting higher viscosity fluids into concordant vertices is extremely difficult due to the internal friction present in highly viscous liquids.

Additionally, in order to split these process liquids, the piping through which the process material flows must be straight, and disturbance or vibration in the pipe may impact the measurement. A vortex flowmeter will be in a fixed installation. This stationary element, operating without electrodes, can be advantageous for flow measurement in chemical applications utilizing low viscosity fluids.

The vortex shedding flowmeter is widely used for the measurement of steam flow. The high pressure and elevated temperature of steam, along with the variation that exists in most steam systems, have little negative impact on the operation of a vortex flowmeter. Vortex shedding flowmeters are volumetrically based in terms of measurement, but their output can be combined with other fluid measurements and data to calculate mass flow. A product variant commonly available will combine the vortex flow measurement with temperature and pressure compensation, delivering three process measurements from a single installed device.

Whatever your flow measurement challenge, share it with process measurement specialists and leverage your own knowledge and experience with their product application expertise.

Operating Principles and Application of Vortex Flowmeters

Vortex Flow Meter
Courtesy Azbil NA

To an untrained ear, the term “vortex flowmeter” may conjure futuristic, potentially Star Wars inspired images of a hugely advanced machine meant for opening channels in warp-space. In reality, vortex flowmeters are application specific, industrial grade instruments designed to measure an important element of a fluid process control operation: flow rate.

Vortex flowmeters operate based on a scientific principle called the von Kármán effect, which generally states that a fluid flow will alternately shed vortices when passing by a solid body. “Vortices” is the plural form of vortex, which is best described as a whirling mass, notably one in which suction forces operate, such as a whirlpool. Detecting the presence of the vortices and determining the frequency of their occurrence is used to provide an indication of fluid velocity. The velocity value can be combined with temperature, pressure, or density information to develop a mass flow calculation. Vortex flowmeters exhibit high reliability, with no moving parts, serving as a useful tool in the measurement of liquid, gas, and steam flow.

While different fluids present unique challenges when applying flowmeters, steam is considered one of the more difficult to measure due to its pressure, temperature, and potential mixture of liquid and vapor in the same line. Multiple types of steam, including wet steam, saturated steam, and superheated steam, are utilized in process plants and commercial installations, and are often related to power or heat transfer. Several of the currently available flow measurement technologies are not well suited for steam flow applications, leaving vortex flowmeters as something of a keystone in steam flow measurement.

Rangeability, defined as a ratio of maximum to minimum flow, is an important consideration for any measurement instrument, indicating its ability to measure over a range of conditions. Vortex flowmeter instruments generally exhibit wide rangeability, one of the positive aspects of the technology and vortex based instruments.

The advantages of the vortex flowmeter, in addition to the aforementioned rangeability and steam-specific implementation, include available accuracy of 1%, a linear output, and a lack of moving parts. It is necessary for the pipe containing the measured fluid to be completely filled in order to obtain useful measurements.

Applications where the technology may face hurdles include flows of slurry or high viscosity liquids. These can prove unsuitable for measurement by the vortex flowmeter because they may not exhibit a suitable degree of the von Kármán effect to facilitate accurate measurement. Measurements can be adversely impacted by pulsating flow, where differences in pressure from the relationship between two or more compressors or pumps in a system results in irregular fluid flow.

When properly applied, the vortex flowmeter is a reliable and low maintenance tool for measuring fluid flow. Frequently, vortex flow velocity measurement will be incorporated with the measurement of temperature and pressure in an instrument referred to as a multivariable flowmeter, used to develop a complete measurement set for calculating mass flow.

Whatever your flow measurement challenges, share them with a flow instrument specialist, combining your process knowledge with their product and technology expertise to develop effective solutions.

Introduction to Flowmeters

Electromagnetic Flow Meter
Courtesy Azbil N.A.

Flowmeters measure the rate or quantity of moving fluids, in most cases liquid or gas, in an open channel or closed conduit. There are two basic flow measuring systems: those which produce volumetric flow measurements and those delivering a weight or mass based measurement. These two systems, required in many industries such as power, chemical, and water, can be integrated into existing or new installations. For successful integration, the flow measurement systems can be installed in one of several methods, depending upon the technology employed by the instrument. For inline installation, fittings that create upstream and downstream connections that allow for flowmeter installation as an integral part of the piping system. Another configuration, direct insertion, will have a probe or assembly that extends into the piping cross section. There are also non-contact instruments that clamp on the exterior surface of the piping and gather measurements through the pipe wall without any contact with the flowing media.

Because they are needed for a variety of uses and industries, there are multiple types of flowmeters classified generally into four main groups: mechanical, inferential, electrical, and other.

Quantity meters, more commonly known as positive displacement meters, mass flowmeters, and fixed restriction variable head type flowmeters all fall beneath the mechanical category. Fixed restriction variable head type flowmeters use different sensors and tubes, such as orifice plates, flow nozzles, and venturi and pitot tubes.

Inferential flowmeters include turbine and target flowmeters, as well as variable area flowmeters also known as rotameters.

Laser doppler anemometers, ultrasonic flowmeters, and electromagnetic flowmeters are all electrical-type flowmeters.

The many application classes throughout the processing industries have led to the development of a wide range of flow measurement technologies and products. Each has its own advantages under certain operating conditions. Sorting through the choices and selecting the best technology for an application can be accomplished by consulting with a process instrumentation specialist. The combination of your own process knowledge and experience with their product application expertise will develop an effective solution.

Liquid Flow Measurement - Magnetic Flow Meters

Magnetic Flow Meter Assembly
Azbil

There are many technologies available for measuring liquid flow in industrial fluid processes. Each method has its own set off attributes that will make it an advantageous selection for some applications. A familiarity with those attributes can help you make an effective selection.

Magnetic flow meters, also called electromagnetic flow meters or "magmeters", operate on a very simple principal. An electrically conductive liquid moving through a magnetic field will generate a voltage that is related to the velocity of the liquid. Magnetic flow meters have no moving parts and present little to no pressure drop to the piping system into which they are installed. It is a flow-through device and does require the cross section of the pipe to be completely filled by the subject fluid in order to produce a useful reading.

Some characteristics of magnetic flow meters.

• Sensor assembly has no moving parts.
• The subject fluid must be electrically conductive.
• Measurement reflects fluid velocity and is not impacted by viscosity, density, or static pressure.
• Other than regular calibration and operational checkout, no maintenance requirements.
• Produces velocity reading only. Need other inputs to produce a mass flow value.
• Bidirectional flow measurement is possible.
• Little or no pressure drop associated with the instrument.
• Comparatively higher in weight.
• Accurate measurements require entire pipe cross section to be full of fluid.

There is more to know. A data sheet is included below that details the Azbil Smart Two-wire Magnetic Flowmeter. For even more information, reach out to a process measurement specialist and share your flow measurement challenges. Combining your process knowledge with their product application expertise will lead to the most effective solutions.

Magnetic flow meter for industrial process measurement from CTi Controltech