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The Merits of Magnetostrictive Level Measurement

February 14, 2016  

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The process instrumentation world possesses a wide variety of challenging level applications. Those responsible for choosing the right instrumentation, for the right application, with the right array of performance, reliability and features and functions face a dizzying array of possible solutions.

This variety is not a bad thing (choices are good). We must understand that multiple options can also mean varying outcomes. While everyone would agree there is not one panacea for all level applications, considering all proven technologies should minimize risk and maximize a successfully implemented solution.

One technology which is often overlooked for difficult applications, where performance, accuracy and reliability are critical, is Magnetostrictive technology. Magnetostrictive is often associated with Magnetic Level Indicators/Gauges given the synergy between the technologies, but Magnetostrictive technology can stand alone in a host of process applications and environments.

Since Archimedes’ famous eureka moment in his bathtub, buoyancy and the principles which support it have been one of the most widely used in the process instrumentation world. It is exceedingly rare, even today, that industrial plants in all markets don’t use buoyancy to measure level; either continuous or point. The attributes of buoyancy, which have created such a mass following, are well deserved. Simplicity, reliability and ruggedness are a few of the characteristics which are associated with buoyancy-based instrumentation. It would be interesting to see Archimedes’ reaction to the advancement in technology over the years, particularly in the instrumentation world. There is no question that this evolution, particularly electronic measurement, has shifted the focus to other forms of level measurement, particularly those that utilize sophisticated electronics.

Magnetostrictive technology combines the best attributes of both buoyancy and electronic-based measurement. On-board electronics send a low-voltage electrical pulse down the magnetostrictive wire at the speed of light. Magnets contained within the float focus their energy toward the wire at the precise location of the liquid level. Interaction between the magnetic field, electrical pulse, and magnetostrictive wire cause a slight mechanical disturbance in the wire that travels back up the probe at the speed of sound. The mechanical wave is converted back into electrical energy by a piezoelectric crystal array. The sophisticated on-board electronics interpret the time-of-flight data and indicate the position of the float magnets.

Organizations today are constantly trying to achieve more with less, squeezing every aspect of their businesses for extra output, additional optimization and extra profit. In many cases, the difference between being competitive and being able to make a measurement is razor thin – literally. In an era of technologically advanced “smart” instruments, plants and operators are investing and placing more reliance in device networks which deliver reliable level measurement with a high degree of accuracy. Magnetostrictive level transmitters are capable of measuring with an impressive accuracy of 0.05 inches (1.27 mm), smaller than the thickness of most coins currently in circulation. This allows facilities tighter tolerances, optimizing their process operations and generating greater ROI.

The advent of smart instruments and digital communication protocols has revolutionized the manner in which setup, configuration, and insight into instrument performance vis-à-vis process conditions is accomplished. When looking at instruments for your operation, the ability to not only utilize software frame programs such as PACTWare, but also the ability to render graphical information directly on the transmitter’s local display, should be of primary consideration. Instruments capable of an enhanced user interface, such as using a full graphic display, as opposed to line by line character displays, have accelerated the path to the next generation of Magnetostrictive transmitter. Users should look for devices with the ability to render resident echo curves, provide context-sensitive help menus, and advanced performance analysis. This affords users greater clarity, decreased time spent “dialing” the instrument in, and help at the instrument when you need it. Whether externally mounted to a level gauge or directly inserted into a vessel, The new Jupiter™model magnetostrictive transmitter from Orion Instruments can deliver deep insight either directly at the transmitter or through a sophisticated user interface on a laptop, communicator, or DCS/host system.

The quest for opportunities often dictates that industrial plants and facilities be located in extreme environments and remote locals. Having reliable, rugged instruments is paramount to minimize downtime and maximize uptime. Users should look for instruments which have encapsulated circuit boards to prevent precipitation attack, separate moisture-proof compartments to mitigate total electronic failure, and environmentally sealed probe/sensor assemblies.

Historically, Magnetostrictive transmitters have been one-dimensional. The transmitter head and the probe were integrally tied to one another as the methodology for separating the incoming signal from the piezo electrical crystals was problematic. In some scenarios, this invariability caused issues, where heat or excessive vibration affected the ability of the instrument to perform at the level it is capable of. Next generation transmitters like the Jupiter™ model JM4, the world’s first two piece Magnetostrictive transmitter, will allow placement of the unit in locations not seen before. It will allow for remote placement of the transmitter head, not only to avoid severe process conditions, but also to allow for a more convenient user experience by allowing the transmitter to be remote mounted up to 12ft/4meters away. Less tank climbing means a safer situation and less time invested. Users will also appreciate instruments which allow adjustability in crowded industrial plant environments. By allowing users to rotate the Jupiter’s head by 310 degrees, operators can position the display in such a manner to allow the greatest view of the display and operation of the unit. With an ergonomically designed dual compartment head angled at 45 degrees reading a transmitter, even in the most crowded environments, is a breeze.

With the introduction of the two piece system, operators now have greater choices in dealing with transmitters in the field. Magnetostriction has always possessed the advantage of being able to be mounted externally to an MLI. As mentioned earlier though, the transmitter and the probe were a single piece. With the new two piece design, Orion introduces auto-configuration to magnetostrictive technology with Jupiter’s new Smart Probe. When the transmitter head connects to a probe for the first time, configuration settings stored within the probe are instantly transferred. This unique capability expedites the setup process and simplifies the task of installing spare transmitter heads on existing or replacement probes.

It is not uncommon to look at magnetostrictive as a technology that is suited to more benign environments and medias. The truth of the matter is that magnetostrictive is well-suited for a wide range of process conditions and medias. Conditions that normally might lead one to steer clear of a buoyancy based device, can be tackled with the right magnetostrictive transmitter. Buildup-prone applications, which would normally give many pause, can be mitigated by the use of an advanced polymer coating, such as Teflon® or Halar® on the magnetic float and probe. Applications that feature high viscosity media can be dealt with by optimizing float design and buoyancy. In addition, Magnetostrictive technology is particularly well suited for two challenging applications:

Unlike many other technologies, particularly those that rely on the propagation of sound or electro-magnetic energy, the buoyancy basis of magnetostriction allows for viability in applications which may see light-to-severe foaming conditions. Since the magnetic float, which activates the magnetostrictive transmitter, is weighted to the specific gravity/density of the media, the foam which is produced in these types of applications is not dense enough to significantly affect the float’s mobility. Units that produce sound or electromagnetic energy can very well find their signals attenuated depending on the density, bubble size and nature of the foam. Use of magnetostrictive technology mitigates the risk and better promotes a successful application.

Arguably the most difficult level measurement, interfaces pose a number of problems for many level technologies. Signal propagation, particularly through the emulsion layer (if one exists) has limitations. Unfortunately, in many interface applications, it is not always known or anticipated that an emulsion/rag layer might exist.

The beauty of buoyancy is the ability to weight a float to a specific density, which means that a float can be designed to either sink completely through the emulsion layer or somewhere in between. Given that the specific gravity of the upper and lower fluid are known, Magnetostrictive is a great choice in these applications. While it might be argued that there could be some amount of discrepancy in the accuracy of the measurement based on changes in specific gravity, there is very little chance that Magnetostrictive technology will experience complete failure in the application, which is possible with other energy propagation measurements.

The repeatability of the measurement will be excellent and, given stability of density, high accuracy is also possible

In summary, Magnetostrictive technology continues to advance at a rapid clip. The latest generation of Magnetostrictive transmitters is being introduced today by Orion Instruments. The new Jupiter™ model JM4 transmitter delivers advanced features, functions, diagnostics, reliability and performance. Orion Instruments, a proven leader in both Magnetostricitve and Magnetic Level Gauge instrumentation, invites you to visit our web site or contact one of our authorized representatives today to discuss how the Jupiter JM4 transmitter can transform your opinion of magnetostrictive technology.