Magnetic Flowmeters: Principles and Applications

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.

Understanding Guided Wave Radar Level Instruments

Guided Wave Radar (GWR)
level transmitter (Drexelbrook)

One of several technologies used for level measurement in process control is guided wave radar. A Guided Wave Radar (GWR) level transmitter combines time domain reflectometry (TDR), equivalent time sampling (ETS), and low power circuitry with a form factor that includes a wave guide extending into the contained media. TDR measures distance or level using pulses of electromagnetic energy. The pulse travels along the waveguide until it reaches the media surface and is reflected back to the unit. The speed of the pulse is known, so an accurate measure of the travel time for the signal can be processed into a distance measurement. Different media will produce a range of amplitude in the reflection, with a greater dielectric difference between air and target medium producing higher amplitude in the reflection. Industries, such as telephone, computer, and power transmission, have relied on TDR for years in order to detect and pinpoint breaks in wires or cables, making the technology more mature than it may appear by its limited timeline in level measurement applications.

ETS is used to measure the high speed, low power electromagnetic energy, and is typical when applying TDR to level measurement technology, where the signal travel distance and time are very short. The electromagnetic signals are captured by the ETS technology in nanoseconds, and are then reconstructed in the equivalent time of milliseconds. The radar scans the waveguide, collecting thousands of samples to be used in signal processing. Integrating both technologies into a single level transmitter yields an accurate and responsive instrument for process measurement.

GWR instrumentation is useful in the process control industry for its ability to measure levels in a quick, consistent way. GWR transmitters are contact radar level measurement tools, as opposed to pulsed non-contact radar transmitters that emit radar pulses through free air without a waveguide. Probes, inserted into the subject tank or vessel, serve as the waveguide for the pulsed signal. They guide the pulsed microwave vertically into the tank, providing a measure of immunity from disturbance by the tank and surrounding media. Guided wave radar technology differs from non-contact radar in a number of ways. The presence or absence of a probe is only one of them.

GWR level transmitters are used in process measurement applications throughout many industries, such as food and beverage. Tanks, pumps, and piping systems for both storage and transport can utilize GWR to continuously monitor levels. Other vessels, such as reduction, forming, mixing, heating, cooking, and cooling, can utilize GWR for similar reasons. Additionally, other stages of food and beverage manufacturing, such as centrifugation and decontamination, can be good fits for GWR technology. Guided wave radarís previous applicability in industries aside from liquid processing and implementation in a wide range of process settings show the flexibility and reliability of GWR technology.

Selecting the best level measurement technology for an application can be a challenge. Share your project requirements and concerns with a process instrumentation specialist, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

7 Reason to Choose Full Flanged, Full Port, Wafer Style Valves

Abstracted from an article by Robert Donnelly of Flo-Tite.

1. Space Savings - Shorter in width than a standard flanged ball valve, the wafer-style ball valve

   

   Flo-Tite Kompact Series Valve

   is ideal for skid systems or any application where space is an issue. Ideal for under tanks too.
2. Lower Torques - With less torque than other con­ventional full-port valves, the wafer valve can be automated by smaller actuators with smaller universal mounting kits.
3. Less Weight - The wafer valve weigh­s about 30% less than full-port flanged ball valves.
4. One Piece Body - If steam jacketing is required, the jackets cost much less than two-piece bolt-on types. 
5. Pocket-less Design - Many process control engineers will not use ball valves because of the dead space behind the valve ball. The pocket-less design of the wafer valve eliminates that concern.
6. Easier to modify flanges to meet standards - When equipment made in Europe is sent to U.S. there is often a need to tran­sition from the DIN flange to an ANSI interface to install the equip­ment here. With the wafer valve, it is relatively easy to modify the flanges to mate.
7. Tapped flanges - Adds to the ease of installation or maintenance as one side of the piping can be re­ moved while the valve is still under pressure.

For more information on Full Flanged, Full Port, Wafer Style Valves contact Piping Specialties, Inc by calling 800-223-1468 or visit http://www.psi-team.com.

Mogas FlexStream: Rotary Control Technology for Severe Service Applications

Process plants have increased throughput causing operating pressures and flow rates to increase as well. Advanced production techniques demand better equipment and valve performance to handle these severe conditions. FlexStream rotary control technology is designed specifically for severe service conditions, to provide superior velocity control, variable characterization, exceptionally high rangeability, and precision modulation.

1) Diffusion element splits and aligns the flow.
2) The control element reduces the flow velocity.

Within a compact replaceable trim design, located downstream with a seat, FlexStream technology employs flow paths of different configurations to control flow and pressure drop. First the diffusion element splits and aligns the flow, then the control element reduces the flow velocity through a variable arrangement of torturous flow path. This allows precise pressure let down, and velocity control custom tailored to process conditions. These torturous flow paths consist of a series of right angle turns. Pressure is reduced by directing fluid flow through these right angles, which control kinetic energy and velocity. Pressure drop at each stage is evenly distributed, while the torturous path expands at each right angle to ensure velocities will not be increased. The larger the pressure drop, the more turns are required to control velocity.

For applications requiring high rangeability, ideal flow control is available by varying the combination of control area and open area, within the trim. The control area determines the amount of bore filled with multi-stage paths, and is used for higher pressure drop lower flow conditions. The open area determines the amount of unrestricted flow, and is used for lower pressure, drop higher flow conditions. This custom fill characterization can vary from 30 to 100 percent, depending on flow conditions, pressure drop, noise level, and outlet velocity required. Precise process and velocity control are achieved at every stage of valve opening, with exceptionally high rangeability in a single control valve.

For gas and steam applications, extreme noise and vibration are reduced or eliminated. The patented FlexStream technology expands upon the strengths of Mogas quarter turn ball valves to offer application-specific trim engineered for high delta-P applications, replaceable control element design, greater Cv per inch compared to the competition, and a smaller dimensional envelope in a traditional control valve.