by Matt Migliore
The latest generation of flow transmitter technology incorporates many levels of diagnostics to simplify process management and instrument maintenance. Photo courtesy of KROHNE Inc.
With an abundance of flow measurement technologies currently on the market, end-users have a lot to consider when evaluating solutions for a given application. Making the task even more complex, the technologies within each flowmeter segment come equipped with widely varying levels of capability. As such, a methodical and well-reasoned approach is required to ensure the biggest bang for the flow measurement buck.
Going Digital
The most prominent technology trend in the flowmeter segment today is the emergence of digital systems. Many flowmeters now come equipped with powerful digital transmitters capable of providing advanced diagnostic information for process verification and plausibility testing of the measurement. Meanwhile, bus communication standards, such as Foundation Fieldbus (www.fieldbus.org) and Profibus (www.profibus.com), have opened up the data highway such that dozens of instruments can now run on a single loop, arming the end-user with more operational information to effectively diagnose and address potential problem areas before they result in process disruption.
While the evolution of flow measurement technology has generally been a positive for the end-user community, today’s instruments are so much smarter than previous iterations of technology that the required level of expertise to operate them has fallen over the years. This has created a situation where many end-user companies no longer have in-house staff with a high-level understanding of the finer points of flow measurement. As such, when faced with the task of evaluating a vast array of new flow measurement technologies, end-users may find themselves struggling to identify the most appropriate solution for their applications.
"From a personal point of view – and this is not generalizing – we see many customers do not have the necessary flow measurement expertise in house," says Eddie Bridges, head of product management for KROHNE Inc (www.krohne.com). "The customer is led to believe that the flowmeter will measure under any circumstances instead of going back to basics and ensuring the best installation and position for the flowmeter, assuming [the end-user] has selected the right flowmeter for the job."
Back to the Basics
Regardless of how sophisticated the underlying technology, end-users should enter into any flowmeter selection process with an understanding of the basic principles of the flow measurement systems they are considering. Likewise, end-users should be careful not to allow the advanced capabilities of a flow measurement system to overshadow the actual needs of the application.
For example, Roushey says he has worked with end-users that have specified Coriolis flowmeters for volumetric flow applications even though Coriolis is a mass measurement technology. As a result, he says the end-user applied a relatively high-end technology for an application that could have received an equal or better level of performance from a lower-cost device.
"The big challenge is matching the customer’s application with the right technology and then convincing the customer of the value the technology can provide for their application," says Roushey. At the same time, he says sales people are as human as the customer, and they are often comfortable with certain technologies as well, which could have a negative impact on the selection process. To prevent such biases, Roushey recommends end-users and sales people only specify technology once they have a firm understanding of the application needs.
"Almost every manufacturer has application data sheets, says Roushey. "Sometimes there’s a tendency to put those on the take it or leave it side and just wing it." However, he says, "The more accurately and precisely the customer completes an application data sheet, the more likely they are going to get the right meter."
Bridges advises those end-users that lack in-house flow measurement expertise to work closely with their suppliers. However, he suggests end-users should choose their suppliers carefully, looking for candidates with strong application experience in their environment.
"Many suppliers are happy to advise and also supply interactive sizing and selection software to help the end-user make the right choice," says Bridges. "This is, however, not a substitute for application experience," he says. "Many of these software packages are not foolproof. They can only steer an end-user in the right direction from the basic process data provided. There is no substitute for process knowledge."
In addition, Bridges says it is often difficult to separate the marketing hype and the claims made by manufacturers from the practical implications of what needs to be measured and what the end-user wants to achieve from the measurement. "The vast number of flowmeters and technologies to choose from makes it more difficult to ensure the choice of the right flowmeter for the job," says Bridges.
Installation Considerations
According to Roushey, three out of four flowmeter performance problems can be traced directly back to improper installation. As such, he recommends end-users carefully document their installation environment prior to specifying the flowmeter. In addition, he says, "Wherever possible, it’s in the customers” best interest that they physically show the supplier where the meter is going to be installed in an existing installation."
Regarding flow measurement, the most important installation issue to consider is upstream and downstream straight-run piping. Roushey says the manufacturer should clearly articulate the piping requirements for the meter to perform up to its capability.
"In today’s world, the meters themselves are very, very accurate and very well put together," says Roushey. "All things being equal, the devices are going to perform within their specified accuracy."
According to Bridges, there is much work and research being done to make meters immune to such process conditions and entrained air, while in reality all the end-user typically needs to do to eliminate the problematic effects of this issue is to carefully consider where the flowmeter is installed in the process line.
"We have seen flowmeters installed almost directly after a pump where the pump is generating a lot of noise, sometimes even sucking in air through the seals, which all ultimately affects the performance of the flowmeter," says Bridges. "The same flowmeter positioned a little further away would provide improved performance."
Another application issue Bridges says he encounters regularly is the specification of unrealistic turndown ratios. He says end-users often rely on what they see on paper rather than evaluating the practical implications of the actual application. "This has led to, in some cases, manufacturers specifying unrealistic headline claims with the small print camouflaging the actual limitations," says Bridges. "If systems are specified, the actual error is the sum of the errors of all the devices used in the measurement system, not just the headline accuracy statement of the main flowmeter device," he says. "If pressure and temperature compensation is included, conversion from volume to mass (or the other way around), then the accuracy statement needs to be relaxed."
The Future
Going forward, both Bridges and Roushey see flow measurement technology continuing to evolve to provide improved performance and reliability and more digital capabilities. "I think that we are living in exciting times," says Bridges. "The quest to find the ultimate flowmeter is driving investment in R&D to all-time highs."
Bridges expects to see significant development specifically in the area of two-phase flow measurement technology, where the devices are intelligent enough to correct for implausible measurement scenarios.
Bridges says he would expect to see some hybrid flow measurement devices coming to market in the future. He says these devices would combine the best capabilities of each technology type to compensate for potential weaknesses in measurement performance. So, when the process conditions are such that the one technology is incapable of providing an acceptable level of performance, the device would intuitively switch over to the measurement method to bring the measurement back in line with the application requirements. As to when we’ll see such hybrid technologies emerging into live application environments, Bridges says, "At the end of the day, it will all come down to the affordability of the technology."
Regarding the price of flow measurement systems, Roushey says the end-user community can look forward to a relatively price stable future. Citing the emergence of magnetic flowmeters in the 1970s, Roushey points out that the going rate at that time was about $1,000 per line inch. Now, he says, magmeters are generally priced at $1,200 per line inch.
Roushey also sees flow measurement technologies continuing to evolve to expand their application range. For example, he says there was a time that Coriolis flowmeters could only effectively support measurements on lines of two inches or less. Now, he says, it’s not uncommon to see Coriolis flowmeters operating on lines up to 10 inches.
Matt Migliore is the editor of Flow Control magazine. He can be reached at [email protected] or 610.828.1711.
