Level-ing with You

Here a K-Tek magnetic level gauge coupled with an SIL2-certified magnetostrictive level transmitter provide level indication and control in a hydrocarbon application.

Photo courtesy of K-Tek Corp

Like most of today’s instruments, level measurement devices have benefited from advances in process communication. While previous level measurement systems were primarily local devices, many of today’s level instruments are capable of plugging into a larger control system and can be managed from a central location.

Kevin Hambrice, director of marketing and customer service for level measurement provider K-Tek Corporation, cites the ability to transmit level data via 4-20 mA, HART, Foundation Fieldbus and other communication methods as a key advance in the recent history of level measurement. For example, he says K-Tek’s magnetostrictive level transmitters come equipped with support for communication protocols, which enable the transport of level measurement information. So, while past iterations of level measurement systems required an operator to manually check the level measurement at the vessel, many of today’s level transmitters can relay this information to the control system so it can be monitored remotely. This is not only a benefit of convenience, but also fosters workplace safety in level applications where harsh and potentially dangerous materials are being handled.

In addition to communication capability, many of today’s level measurement systems are easier to install, configure and maintain. For instance, whereas previous generations of level technology typically required a fair amount of technical knowledge to properly install and configure, the software available for today’s level measurement systems is sophisticated enough that just about anybody can commission the device.

Sarah Parker, an application manager for Emerson Process Management’s Rosemount Division, says diagnostics are also a key advance in the level measurement category. "Devices have their own self-check, so if something is wrong, the device will tell you that something is wrong," she says. Parker says some of the key diagnostics for today’s radar level measurement systems specifically include signal strength, level measurement status, including validity of the measurement, fill or empty tank status, and process changes such as the appearance of foam or turbulence.

Looking at the available level measurement technologies in a broader sense, Parker says the emergence of radar has been an important advance in the level measurement segment. "Fifteen years ago radar didn’t even exist in the process world, Now it is seen as a cost-effective, accurate solution that is immune to density and other process fluid changes as well as most vapor space conditions," says Parker. And while she acknowledges it has taken some time for end-users to gain the understanding required to facilitate more widespread use of radar level, she says the technology has reached an acceptance level where you are hearing of it more and more as a standard solution.

Radar level measurement systems are available in contacting and noncontacting versions. Contacting devices are called guided-wave radar (GWR). In her experience, Parker says GWR systems have received more widespread use than noncontact radar, in part because they are capable of providing interface level measurement (e.g., oil & water), as well as standard direct level measurements.

K-Tek’s Hambrice cites interface measurement as an area of marked improvement when comparing new technologies to older methods of level measurement, such as, for example, hydrostatic tank gauging. According to Hambrice, hydrostatic systems for interface level applications can range from 1 percent to 25 percent accuracy in a dynamic process environment, while the latest generation of magnetostrictive technology is capable of 0.010 percent to 0.25 percent accuracy in the identical interface application.

Finding the Right Level Solution
Hambrice believes one of the most important considerations end-users can make when specifying magnetic level gauge technology in particular is in the manufacture of the float. A magnetic level gauge relies on a float to arrive at a level measurement. If the float is designed specifically to suit the process medium being measured, Hambrice says the end-user can realistically expect to see 30-40 years of reliable service from a magnetic level gauge. On the other hand, he says if float construction is not properly considered when specifying a magnetic level gauge, the performance and reliability of the system may suffer dramatically.

The Rosemount guided-wave radar system pictured here is being used to provide a level measurement on a high-temperature fuel buffer tank at a refinery in Asia.

Photo courtesy of
Emerson Process Management

Regarding radar level technology, Rosemount’s Parker says the first step end-users will want to make is to determine if their application is best suited for a noncontacting or a contacting radar device. Parker says contact radar (i.e., GWR) is generally a good fit for small spaces and as an easy replacement for existing level systems such as capacitance and displacers, while non-contacting radar is generally a better fit for dirty, viscous and/or corrosive applications, and where there are agitators. (As noted earlier, GWR also provides the added benefit of being able to support interface level applications.)

When specifying level measurement systems in general, Hambrice says the end-user must resist the temptation to focus on the bells and whistles of a given product at the expense of the core goals of the application at hand. "One of the things you have to be mindful of is that the product itself is less important than the solution you’re trying to achieve," he says.

For process level measurement applications, Hambrice says end-users should ask themselves the following questions when specifying a system:

• What kind of accuracy am I looking for?
• What is the temperature, pressure, media type?
• What is the temperature range of the application?
• What is my budget?

In addition, Hambrice says end-users should look for a supplier with a broad range of level measurement solutions so they can identify the appropriate solution for the application rather than just pushing a product. From a service and support perspective, he says end-users should also look for a supplier with a support presence in their area, as well as a range of online tools for commissioning, installing, and troubleshooting the level measurement system.

Rosemount’s Parker says end-users should look for a level measurement solution that is low maintenance, easy to use, and helps guide the user through the setup process. Also, there are some more difficult applications where extra functionality is helpful. For example, she says end-users working with steam applications of more than 400-500 PSI should look for GWR systems that have a dynamic vapor compensation method to ensure the accuracy of the device in such an environment. Similarly, in applications where the signal reflection is weak, the device should be able to provide an alternative measurement, such as probe end projection, where the unit uses a combination of the known length of the probe and an online measurement of dielectric of the material to determine level. And on the maintenance side, Parker says end-users that have identified GWR as a good fit for their application should give special consideration to the device’s probe and signal strength if the process medium is dirty. Twin and coaxial probes are susceptible to clogging and buildup, so Parker suggests end-users look for a device that is capable of using a single-lead probe so that maintenance can be minimized if a dirty medium is being measured. The addition of signal quality diagnostics can help the user determine if probe cleaning is needed and allow maintenance to be scheduled only when needed.

Common Application Pitfalls
In Parker’s experience, the most common application pitfall she encounters when working with end-users on radar is the installation itself. When a level device is considered for an application, the functional capabilities of the device need to be considered in addition to installation constraints and process conditions. For example, she says end-users will place a new radar level system on an existing nozzle. In such cases, Parker says the existing nozzle is often found to be too tall or too narrow for the instrument. "[Radar] devices need a certain amount of space to operate well and generate a good signal," says Parker.

Parker recommends users try to minimize the height of the nozzles they are using with a radar level system. For example, she says, ideally a two-inch nozzle should be no more than six inches high for GWR. For non-contacting radar, it is preferable that the end of the antenna extends slightly beyond the end of the nozzle. (Antenna lengths will vary with diameter, frequency and antenna type. Users should work with the supplier to find an optimal solution.) Likewise, she says a two-foot high nozzle is generally not going to be a good fit for many radar level systems.

As such, Parker says users should try to provide the manufacturer with their existing nozzle dimensions when they are specifying a radar level system. Unfortunately, she says end-users often know the size of the flanges, but not the height of the nozzle, and it only becomes apparent that there is an issue with the nozzle once the system is in place.

Parker says another common installation problem she encounters is when the radar system is installed in a nozzle that is positioned directly over a pipe, baffle or some other obstruction. As such, the obstruction becomes the level measurement rather than the surface of the process medium in the vessel. To avoid such occurrences, Parker says to consider what would happen if you were to shine a flashlight through the nozzle. If there is a clear view of the surface of the process medium in the vessel, then you can go ahead and install the radar device. However, if there is an obstruction in the path, then the end-user would be wise to find a different location for the installation. Similarly, if the fluid stream coming into the tank falls into the beam path or on the probe, then this could impact the reliability of the level measurement.

On the configuration end, Parker says the end-users should make a special effort to ensure the height settings and thresholds for the radar signal are in accordance with the application needs. For example, she says users could run into problems with their measurement if, for example, they set up their radar level device with water and they are using it to measure oil. "Oil looks different to a radar level gauge than water does, and the threshold setting needs to correspond," says Parker.

Hambrice says while some traditional methods of level measurement offer a low up-front cost, this does not make up for the performance and safety issues they present when compared to current-generation level measurement solutions. He suggests end-users look at three key factors when evaluating their level measurement systems:

• Safety
• Efficiency & Reliability
• Environmental

To ensure the proper specification of a level measurement system, Hambrice says end-users should provide the manufacturer as much application information as possible. For example, he says if the application involves a dirty fluid with buildup possibilities, then a float-based approach will require special considerations; or, for instance, if the application is susceptible to a high vibration levels, he says a reed switch technology would probably not be an ideal solution.

"That’s why we ask so many questions during the consultation process – the more info we have, the better we’re able to provide an effective solution," says Hambrice.

The Future
Going forward, Hambrice expects to see more support for protocols in level measurement systems. Currently, K-Tek supports most major communications protocols, including 4-20 mA, HART and Foundation Fieldbus. In addition, it recently released its first SIL2 (Safety Integrity Level 2)-certified magnetostrictive transmitter, and Hambrice says the company is now pushing to have all of its transmitters SIL2 rated.

Meanwhile, he also expects to see more multi-lingual devices. "We live in a global world, we need to have instruments that can speak lots of different languages," says Hambrice. K-Tek’s latest generation of level transmitters support up to seven different languages.

Finally, Hambrice sees level instruments incorporating more digital features, as well as leveraging wireless in creative ways to provide additional application visibility and flexibility.

Parker says she sees devices becoming easier and easier to use in the future, eventually reaching a point where they offer pushbutton setup capability.

In addition, she says end-users can look forward to increasing signal sensitivity in the area of radar level measurement, as well as the ability to automatically compensate for more changing process conditions. For example, she says end-users can look forward to radar devices that have sensors capable of detecting the dielectric change of the upper medium in interface applications and automatically compensating to ensure the accuracy of the measurement.

Matt Migliore is the editor in chief of Flow Control magazine. He can be reached at 610.828.1711 or [email protected].