Magnetic Level Indicators (MLIs) and Bridle Combination Units

Magnetic level indicators provide highly visible indication of level with or without signal outputs monitoring tail and vessel level. The term bridle is used to describe a vertical pipe connected to the side of a storage tank or process vessel, most often with side-to-side or side-to-bottom connections. Because the fluid inside the bridle rises and falls equally with the level of fluid inside the tank or vessel, bridles have been adapted for level measurement use on a broad scale.

Below is a good instructional reference document (courtesy of VEGA) on how magnetic level indicators (MLIs) are installed and how they work.

Download the "Magnetic Level Indicators and Bridles for Level Measurement and Visualization" document here.

Magnetic Level Indicators (MLIs) and Bridle Combination Units from Classic Controls, Inc.

Continuous Liquid Level Measurement Technologies Used in Industry

Magnetic level indicator coupled with
guide wave radar level transmitter
Courtesy Vega

Although continuous level measurement technologies have the ability to quantify applications for bulk solids, slurries, and granular materials, liquid level technologies stand out as being exceptionally crucial to the foundation of process control. Called “transmitters,” these continuous liquid level measurement devices employ technologies ranging from hydrostatics to magnetostriction, providing uninterrupted signals that indicate the level of liquid in a vessel, tank, or other container.

Hydrostatic devices focus on the equilibrium of dynamic and static liquids. There are three main types of hydrostatic transmitters: 1) displacer, 2) bubbler, and 3) differential pressure.

The displacer transmitters utilize a float placed within the liquid container. With its buoyancy characterized to the liquid and the application, the float, a connecting stem, and a range spring or similar counterbalance represents the liquid level in terms of the movement of the displacer (float). The displacement, or movement, of the assembly is converted into an electric signal for use by the monitoring and control system.

Bubbler transmitters are used for processing vessels that operate at atmospheric pressure. This method introduces a purge gas or an inert gas, e.g. air or dry nitrogen, into a tube extending into the liquid vessel. Precise measurement of the pressure exerted on the gas in the dip tube by the liquid in the tank is used to determine the height of the liquid.

Differential pressure (DP) transmitters rely directly on, in a basic explanation, the pressure difference between the bottom and top of the container. Precise pressure measurement is used to determine the height of the liquid in the tank. One of the most advantageous aspects of DP transmitters is that they can be used in pressurized containers, whereas displacer and bubbler transmitters cannot.

Other examples of level transmitter technologies––which are not hydrostatic devices––are magnetostrictive, capacitance, ultrasonic, laser, and radar.

In magnetostrictive level transmitters the measuring device, a float, has a series of magnets that create a magnetic field around a wire enclosed in a tube. Electrical pulses sent down the wire by the transmitter head product a torsional wave related to the position of the float, which moves with changes in liquid surface level. The transit time of the torsion wave back to the sensing head is measured and the depth of the liquid, as indicated by the float position, can be determined.

Capacitance transmitters are best applied to liquids that have high dielectric constants. Essentially, changes in the capacitance of the sensor / tank / liquid assembly will vary proportionately with the liquid level. The change in capacitance is measured and converted to an appropriate electrical signal.

Ultrasonic level transmitters emit ultrasonic energy from the top of the vessel toward the liquid. The emissions are reflected by the liquid surface and them time required for the signal to return to the source is used to determine the distance to the liquid surface.

Laser level transmitters operate similarly to an ultrasonic level transmitter. However, instead of using ultrasound signals, they use pulses of light.

Radar level transmitters involve microwaves emitting downward from the top of the container to the liquid’s surface and back again; the measurement is the entire time-frame. One variable radar level measurement echoes capacitance measurements: they both involve dielectric contact of liquid.

The precise measurement of transmit time for a wave or pulse of energy is employed in several of the technologies, the measurement of pressure in others. Each technology has a set of attributes making it an advantageous selection for a particular range of applications. Share your liquid level measurement challenges with an application expert, combining you process knowledge with their product application expertise to develop effective solutions.

Frequency Matters For Radar Level Measurement Applications

VEGAPULS 64 80 GHz Radar level measurement transmitter,
shown in one of twelve mounting forms
Courtesy VEGA

Level measurement in tanks and vessels of all types and sizes is a common component of liquid processing operations. For continuous monitoring of liquid level, radar based instruments and transmitters are a newer and faster growing technology. Their ability to perform well under a range of conditions that can prove challenging to other technologies, coupled with their non-contact measuring attribute, make radar level transmitters an advantageous choice for many applications.

Radar based instruments operate within specific frequency ranges. The different operating frequencies can have an impact on instrument cost, size, configuration, and application suitability.

Greg Tischler, Product Manager - Radar at VEGA Americas, a leader in level measurement instrumentation, authored a white paper detailing the application advantages of the more recently deployed 80 GHz radar level instruments. The bulk of the article is excerpted below, or you can read the entire white paper.

The excerpt.....

Focus

This is the alpha benefit of 80 GHz radar; the one that makes the others possible. In every process, signal focus is crucial to accurate level measurement, and these new instruments emit the most focused signals on the market.
Plant operators have struggled with unfocused radar for decades. The wide beam angle of 26 GHz sensors (and 6 GHz sensors before them) made it difficult for radar signals to miss agitators, heating coils and other vessel internals. The reflections from these installations distorted the echo curve and users were forced to make adjustments to monitor the true liquid level. The new high-transmission models have narrower beams that miss vessel installations—it’s as if they aren’t even there. That is welcome news in chemical and food production, where obtrusive internals are the norm and space is at a premium.

Superior focus makes for accurate measurement without adjustment, but it also opens the door for two other major benefits.

Small process fittings make 80 GHz
sensors effective on small tanks.
Courtesy VEGA

Size

Because their focus is amped up, 80 GHz sensors have small antennas. The new VEGAPULS 64, for example, has the world’s smallest antenna and doesn’t require a large horn to focus its beam at the measured material. The instrument’s small size makes a huge impact, particularly as it applies to retrofitting. Plants can now integrate the most advanced radar devices into their process without shelling out thousands for modifications to their vessels. Smaller instruments, however, aren’t just good for old vessels; they can also help manufacturers stay nimble and market-responsive.

There’s a trend in the pharmaceutical and chemical industries toward batch production. Batching allows operators to produce seasonal and low-volume products with less financial investment. Small batches are produced in small vessels, where conventional wisdom says using radar is impossible due to small process connections. Thanks to the compact design of 80 GHz radar sensors, that is no longer true, and operators no longer have to sacrifice accurate measurement in the name of space. 

Resolution

Imagine looking at the picture on a standard definition television next to that of an HD TV. The high definition picture would be clearer, sharper, and more detailed due to enhanced resolution. Users will see a similar difference switching from low-frequency to high-frequency radar sensors.
When the level of liquid in a vessel gets low enough, 26 GHz radar reads the echo from the material and the echo from the tank bottom as one echo. This tells the user the vessel is empty when it isn’t and presents a natural handicap to process efficiency. 80 GHz devices measure liquid down to the last millimeter, giving users accurate data they can use to optimize their processes. Greater resolution is particularly important for shipbuilders, who count on precise level in large ballast tanks.

Thanks to Mr. Tischler of VEGA Americas for authoring the white paper excerpted in this article. Share your level measurement challenges with product application specialists, combining your own process knowledge with their product application expertise to develop effective solutions.

The Focus of 80 GHz Radar Level Instruments Applied to Bulk Solids

VegaPuls 69 - 80 GHz radar level transmitter for bulk solids
Courtesy VEGA

Level measurement of  bulk solids presents a range of challenges to process designers and operators. One instrument manufacturer, VEGA, has produced a video demonstrating a distinct advantage of utilizing 80 GHz radar level transmitters instead of those with lower operating frequencies. The demonstration shows actual instruments in use, along with displays of the actual output from the device. You should find it useful.

VEGA manufactures a wide range of instruments for measuring level, interface, density, and pressure for process control applications. Share your process measurement challenges with product application specialists, and combine your process knowledge with their product expertise to develop effective solutions.

Radar Liquid Level Measurement Through a Sight Glass

Radar level control installed at tank sight glass
Courtesy VEGA

Level measurement, ubiquitous throughout processing operations, can be accomplished through the use of a number of different technologies. VEGA, a globally recognized innovator in level measurement, has authored a white paper outlining how radar level measurement instruments can be successfully employed when installed on tanks with sight glasses. The white paper is excerpted below, and you can access the full article and a wealth of application expertise by reaching out to an application specialist.

The balance of this article is excerpted from "Using radar sensors to measure liquid level through sight glasses", released by VEGA on 10/25/2016.

Vessels with sight glasses permit users to measure liquid level in a unique way: by mounting a radar sensor above the glass. Radar instruments emit microwaves that penetrate the glass, reach the product inside, and reflect through the glass back to the sensor. This eliminates two major expenses because users are spared from retrofitting a tank to accommodate a sensor and can continue running a process during installation. Functionally, nothing changes as users can simply move the sensor for a moment to look through the glass and see what’s happening inside a vessel.

Challenges to radar level measurement through sight glass

Any radar sensor can measure liquid level through a sight glass, but what happens after a signal penetrates glass varies depending on the sensor. Glasses are often welded, bolted or clamped directly onto a vessel wall or roof with a circular flange, while others are mounted on a nozzle. Radar sensors with a transmission frequency of 26 GHz release wide beams that contact the sides of the flange, the nozzle, and sometimes the roof of the vessel itself. This creates noise at the top of the output, especially on taller nozzles, forcing operators to leave empty space inside a tank to make a clear distinction between the signal received from the vessel and the signal received from the product.

Further complicating the use of 26 GHz sensors with sight glasses is the fact that most sight glasses are installed at a natural slope in the tank. Angled glasses narrow the path to the liquid, increasing the degree of difficulty in setting up a sensor so the beam is perpendicular to the product. Perpendicularity is important because it’s in direct relationship to the strength of the signal the sensor receives. However, to minimize the small signals that bounce from the glass to back the sensor, it’s recommended that users pair a 26 GHz radar sensor with a sight glass installed at a 45° angle. This forces users to choose between a strong signal from the product accompanied by reflections from the glass or a weak signal from the product and no reflections for the glass. Neither scenario is ideal.

Enhanced signal focusing makes all the difference

The problem of noise from fittings and narrow paths can be solved by installing a radar sensor that operates at a higher transmission frequency and produces a more focused signal. The VEGAPULS 64, for example, has a frequency of 80 GHz and can emit a beam angle of only 3°. 26 GHz sensors, on the other hand, emit beam angles of approximately 10°. A narrow beam angle misses the sides of the flange and the nozzle, silencing signal noise. That same focused beam can travel a tight path to the product without sacrificing signal strength. Finally, 80 GHz radar sensors don’t need sight glasses at extreme angles to minimize reflected signals, as a sight glass installed at a 5-10° angle will do.

Other benefits of external level instruments

All this is welcome news to processes where sight glasses already exist and is also noteworthy for those struggling with level measurement technology in traditional tanks. Users in the latter camp may find it more economical to install an external radar level sensor and a sight glass than a new internal instrument because removing a sensor from the interior of a vessel presents users with several benefits. In applications involving harsh, caustic liquids, there’s no risk of the product damaging the sensor with a quick splash or corroding it over time through buildup. This saves users in routine maintenance costs, and lack of exposure extends a sensor’s life. Users can mount a radar sensor above such tanks, and the emitted microwaves penetrate the glass and reliably measure the harsh liquid inside.

External access to a level measurement instrument is also useful for a quick repair or recalibration. With the sensor on the outside of the vessel, users can keep the plant’s process moving while they perform routine maintenance. If a problem arises with an instrument inside of a tank, that particular tank—or worse, an entire line—might have to be shut down, potentially leading to thousands of dollars in lost production. What company can afford that?

Summary

In conclusion, radar sensors of any transmission frequency can be mounted above sight glasses for accurate, non-contact level measurement. Separation from the product helps preserve sensors, and the instruments are easy to access when calibration and maintenance are necessary. When researching their options, users should consider 80 GHz sensors because they emit focused radar beams that take a narrow path to the liquid and fewer signals are reflected by flanges and mounting nozzle interiors. Given radar technology’s accuracy and reliability, and all that can go wrong if an internal level measurement fails, a radar sensor mounted above a sight glass offers nothing but advantages.

A Step Forward in Non-contact Radar Liquid Level Measurement

VEGAPULS 64 80 GHz Radar Liquid Level Sensor

Employing non-contact level measurement in a process control operation has many potential benefits. Radar level measurement has gained acceptance as an accurate and reliable method of liquid level measurement. The process measurement instrumentation manufacturers have continually made strides in the evolution of their product offerings, providing more effective lower cost solutions.

VEGA, a global leader in the manufacture of level and pressure instrumentation for the process industry, has introduced a new radar liquid level sensor. The VEGAPULS 64 operates at 80 GHz, a substantially higher frequency than previous models. The higher radar frequency, along with some other improvements, deliver operational benefits.

Tight beam focus accommodates
vessel internal fixtures
Courtesy VEGA

• Measurement is unaffected by condensation or buildup on the antenna
• High measurement certainty with product deposits on vessel walls
• System is quickly available for operation after cleaning cycles
• Tight focusing of the radar beam on the liquid surface provides easier setup and commissioning with complex vessel internal fixtures.

The radar level sensor is available with a number of connection fitting sizes, extending down to 3/4", which enable retrofitting of this improved technology to smaller vessels without extensive modification. There is also an encapsulated antenna variant that is suitable for hygienic or chemical applications.

There is more to learn about the advances in radar level sensors. Reach out to product specialists for more information. Share your level measurement challenges with the product specialists, then combine your process expertise with their product knowledge to produce effective solutions.

VEGAPULS 64 Encapsulated Version