Basics of Magnetic Flowmeters

Magnetic flowmeter
(Azbil)

Crucial aspects of process control include the ability to accurately determine qualities and quantities of materials. In terms of appraising and working with fluids (such as liquids, steam, and gases) the flowmeter is a staple tool, with the simple goal of expressing the delivery of a subject fluid in a quantified manner. Measurement of media flow velocity can be used, along with other conditions, to determine volumetric or mass flow. The magnetic flowmeter, also called a magmeter, is one of several technologies used to measure fluid flow.

In general, magnetic flowmeters are sturdy, reliable devices able to withstand hazardous environments while returning precise measurements to operators of a wide variety of processes. The magnetic flowmeter has no moving parts. The operational principle of the device is powered by Faraday's Law, a fundamental scientific understanding which states that a voltage will be induced across any conductor moving at a right angle through a magnetic field, with the voltage being proportional to the velocity of the conductor. The principle allows for an inherently hard-to-measure quality of a substance to be expressed via the magmeter. In a magmeter application, the meter produces the magnetic field referred to in Faraday's Law. The conductor is the fluid. The actual measurement of a magnetic flowmeter is the induced voltage corresponding to fluid velocity. This can be used to determine volumetric flow and mass flow when combined with other measurements.

The magnetic flowmeter technology is not impacted by temperature, pressure, or density of the subject fluid. It is however, necessary to fill the entire cross section of the pipe in order to derive useful volumetric flow measurements. Faraday's Law relies on conductivity, so the fluid being measured has to be electrically conductive. Many hydrocarbons are not sufficiently conductive for a flow measurement using this method, nor are gases.

Magmeters apply Faraday's law by using two charged magnetic coils; fluid passes through the magnetic field produced by the coils. A precise measurement of the voltage generated in the fluid will be proportional to fluid velocity. The relationship between voltage and flow is theoretically a linear expression, yet some outside factors may present barriers and complications in the interaction of the instrument with the subject fluid. These complications include a higher amount of voltage in the liquid being processed, and coupling issues between the signal circuit, power source, and/or connective leads of both an inductive and capacitive nature.

In addition to salient factors such as price, accuracy, ease of use, and the size-scale of the flowmeter in relation to the fluid system, there are multiple reasons why magmeters are the unit of choice for certain applications. They are resistant to corrosion, and can provide accurate measurement of dirty fluids ' making them suitable for wastewater measurement. As mentioned, there are no moving parts in a magmeter, keeping maintenance to a minimum. Power requirements are also low. Instruments are available in a wide range of configurations, sizes, and construction materials to accommodate various process installation requirements.

As with all process measurement instruments, proper selection, configuration, and installation are the real keys to a successful project. Share your flow measurement challenges of all types with a process measurement specialist, combining your process knowledge with their product application expertise to develop an effective solution.

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.

Differential Pressure Transmitter Inferential Applications

Differential pressure transmitter for industrial
process control applications.
Image Courtesy Azbil North America

Differential pressure transmitters are utilized in the process control industry to represent the difference between two pressure measurements. One of the ways in which differential pressure (DP) transmitters accomplish this goal of evaluating and communicating differential pressure is by a process called inferential measurement. Inferential measurement calculates the value of a particular process variable through measurement of other variables which may be easier to evaluate. Pressure itself is technically measured inferentially. Thanks to the fact numerous variables can be related to pressure measurements, there are multiple ways for DP transmitters to be useful in processes not solely related to pressure and vacuum.

An example of inferential measurement via DP transmitter is the way in which the height of a vertical liquid column will be proportional to the pressure generated by gravitational force on the vertical column. The differential pressure transmitter measures the pressure exerted by the contained liquid. That pressure is related to the height of the liquid in the vessel and can be used to calculate the liquid depth, mass, and volume. The gravitational constant allows the pressure transmitter to serve as a liquid level sensor for liquids with a known density. A true differential pressure transmitter also enables liquid level calculations in vessels that may be pressurized.

Gas and liquid flow are two common elements maintained and measured in process control. Fluid flow rate through a pipe can be measured with a differential pressure transmitter and the inclusion of a restricting device that creates a change in fluid static pressure. In this case, the pressure in the pipe is directly related to the flow rate when fluid density is constant. A carefully machined metal plate called an orifice plate serves as the restricting device in the pipe. The fluid in the pipe flows through the opening in the orifice plate and experiences an increase in velocity and decrease in pressure. The two input ports of the DP transmitter measure static pressure upstream and downstream of the orifice plate. The change in pressure across the orifice plate, combined with other fluid characteristics, can be used to calculate the flow rate.

Process environments use pressure measurement to inferentially determine level, volume, mass, and flow rate. Using one measurable element as a surrogate for another is a useful application, so long as the relationship between the measured property (differential pressure) and the inferred measurement (flow rate, liquid level) is not disrupted by changes in process conditions or by unmeasured disturbances. Industries with suitably stable processes – food and beverage, chemical, water treatment – are able to apply inferential measurement related to pressure and a variable such as flow rate with no detectable impact on the ability to measure important process variables.

Share your process measurement challenges with instrumentation specialists, leveraging your own process knowledge and experience with their product application expertise to develop an effective solution.

Industrial Transmitters for Pressure and Differential Pressure from CTi Controltech

Dual Input Industrial Temperature Transmitter - What You Can Do

Dual input advanced industrial transmitter
has many built in functions
Courtesy Azbil

You will likely find temperature measurement to be a part of almost every industrial process. It is a mainstay of commercial and industrial processes and operations globally. Accurate measure of process, equipment, or product temperature provides operators with useful information that is utilized in countless ways. The range of available instruments and equipment for measuring temperature in industrial process settings is extensive, with devices or varied types, performance, and form factor to accommodate every application.

There are a variety of instruments and methodologies for measuring temperature, the most common of which is probably direct contact between the target substance and an appropriate temperature sensor. Industrial process applications are commonly served by thermocouples or resistance temperature detectors (RTD), chosen for their cost, accuracy, and flexibility of installation.

Every operating process is "critical" to some group of stakeholders. The process may be of great importance for a number of reasons:

• The process output may serve as an input to another process with great value.
• The process output may be of great direct value to the stakeholders.
• The process may have significant levels of hazard associated with improper or out of control operation.
• Out of control operation may result in substantial financial loss to the stakeholders.

When temperature is an important indicator of process function, whether for financial or safety reasons, the operator cannot tolerate a loss of the temperature signal. One manufacturer has an advanced solution in the form of a dual input temperature transmitter with built in functions that:

• Switch to the backup sensor if the primary has a failure indication.
• Alert the operator if the deviation between the two sensor readings indicates sensor drift. 
• In wide range temperature applications, switch between sensors with differing measurement ranges for better accuracy.

Along with HART communications and other useful features, these advanced temperature transmitters can help reduce risk and increase performance and safety. Assess how these advanced devices can enhance your process performance. A product data sheet is included below. Product specialists can help with product configuration and selection, along with any application concerns you may have.

Advanced Industrial Temperature Transmitter from CTi Controltech

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.

Advanced Pressure Transmitters for Process Measurement

Direct mount pressure transmitter
Courtesy Azbil

The measurement of pressure is a common task throughout many industrial spheres. Depending on the application, a wide range of process or machinery operation status can be derived from a pressure reading. Accuracy, ruggedness, and flexibility in application are hallmarks of a useful pressure transmitter.

Azbil North America advanced pressure transmitters offer a combination of features that can make them an advantageous selection for almost any application.

• Stability of +/-0.1% for 10 years
• Little to no downtime for calibration
• Sensor technology that provides day-one accuracy for the life of the transmitter
• Customizable display
• Alarm outputs
• Fast response
• International standard certifications

The advanced pressure transmitter is available in variety of mounting configurations to suit most applications. More information is contained in the document included below. Share your process measurement challenges with application experts, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Advanced Direct Mount Pressure Transmitter from CTi Controltech

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

Vortex Gas Flowmeter With Built-in Pressure and Temperature Compensation

Azbil MVF Series Vortex Gas Flowmeter

Industrial process control operations require measurement, lots of measurement. Whether it be temperature, level, flow, pressure, or some other attribute of the process, manufacturers have always responded to customer demand with a broad array of engineered products geared toward higher performance and lower cost.

Combining related measuring functions or capabilities into a single device can result in space and cost savings, as well as simplifying maintenance operations. Azbil NA does just that with their MVF Series of vortex flowmeters for gases.

Vortex flowmeters are based upon the recognized principle of vortices being generated downstream of a blunt obstruction at a frequency dependent upon the velocity of the fluid (von Kármán effect). The fluid velocity can be combined with temperature and pressure measurements to produce a calculated mass flow. Azbil, in their MVF Series, provides built in compensation for temperature and pressure, eliminating the need for additional instrumentation. The vortex gas flowmeter provides an output signal that is proportional to the mass flow, as well as a pulse signal. The flowmeter is suitable for use with air, nitrogen, argon, oxygen, carbon dioxide, city gas (13A), methane, propane, butane, and other inert gases or mixtures outside the explosion limit range.

See the data sheet below for more detail. You can also contact product application specialists for any assistance needed to select the right configuration for your application. Share your process measurement and control challenges with product experts. Combine your process expertise with their product application knowledge to produce the most effective solutions.

Vortex Gas Flowmeter for Process Measurement from CTi Controltech

Dual Input Temperature Transmitter Has Some Useful Applications

Advanced Temperature Transmitter
Courtesy Azbil N.A.

Temperature measurement is a mainstay of many commercial and industrial processes and operations. Much can be deduced from an accurate measure of process temperature, and a large segment of the industrial control products marketplace is devoted to reliable and accurate measurement of temperature

There are a variety of instruments and methodologies for measuring temperature, the most common of which is probably direct contact between the substance under scrutiny and a temperature sensor of some type. In industrial process applications, contact sensors are often thermocouples or resistance temperature detectors (RTD), chosen for their cost, accuracy, and flexibility of installation.

Every operating process is "critical" to some group of stakeholders. The process may be of great importance for a number of reasons:

• The process output may serve as an input to another process with great value.
• The process output may be of great direct value to the stakeholders.
• The process may have significant levels of hazard associated with improper or out of control operation.
• Out of control operation may result in substantial financial loss to the stakeholders.

When temperature is an important indicator of process function, whether for financial or safety reasons, the operator cannot tolerate a loss of the temperature signal. One manufacturer has an advanced solution in the form of a dual input temperature transmitter with built in functions that:

• Switch to the backup sensor if the primary has a failure indication.
• Alert the operator if the deviation between the two sensor readings indicates sensor drift. 
• In wide range temperature applications, switch between sensors with differing measurement ranges for better accuracy.

Along with HART communications and other useful features, these advanced temperature transmitters can help reduce risk and increase performance and safety. Assess how these advanced devices can enhance your process performance. A product data sheet is included below. Product specialists can help with product configuration and selection, along with any application concerns you may have.

Advanced Industrial Temperature Transmitter from CTi Controltech

Multivariable Vortex Flowmeter

AX Series Flowmeter
Courtesy Azbil North America

Azbil North America recently added the AX series of multivariable vortex flowmeters for industrial process measurement and control to their product offering. The instrument combines temperature, pressure and velocity measurement in a single instrument to provide accurate mass flow measurement of gases, liquids and steam. Incorporating several variable measurements into a single package reduces potential leakage points, installation complexity, and space requirements compared to arrangements with discrete instruments for each variable. Configurations for in-line or insertion installation are available for line sizes ranging from ½” to 8” for in-line and 2” and greater for insertion. A sizing guide, application and product configuration assistance is available from a product specialist.

Multivariable Vortex Flowmeter from CTi Controltech