However, E+H is finding that ultrasonic level measurement isn’t the preferred technique among chemical customers. “This is because the media to be measured [are] usually very corrosive and therefore conditions cannot ensure repeatability. In addition, vapors which occur within the chemical processes may lead to accuracy problems. And last but not least, the ultrasonic level devices will not work on vacuum systems and above three bar: all of which are also common within the chemical industry,” notes Brian O’Connell, a sales engineer based in Kildare, Ireland.
“Regarding the differential pressure technique, regardless of the industry, this device is not easy to install and therefore may lead to accuracy issues if not installed properly. The media within the chemical processes are not always stable, therefore the density changes, which again may lead to accuracy issues. And finally, customers may have issue with the poor turndown of this device, again a limited ability to measure a wide range,” cautions O’Connell.
However, he adds an important proviso to his observations: “These points are general statements. Of course, with the right installation and a very good understanding of the application and the requirements from the customers, these solutions can be successful.”
More Accuracy And Repeatability
“For level measurement requirements in the chemical industry, we have seen the focus shift towards accuracy and repeatability,” says Lee Aiken, product marketing manager for MTS Systems, Sensors Division, Cary, N.C.
This drive for more accuracy and repeatability has proved a boon the company’s magnetostrictive level transmitter technology. Originally invented and used for linear displacement applications such as motion control and machine automation, the technology was adapted by MTS for measuring liquid levels (Figure 1). Its instruments can check product level, interface level and temperature using one process opening and one transmitter. Their quality is higher than competitors, claims the company
“If you compare this [transmitter] with a reed-switch transmitter they will be very similar until you look at the accuracy and repeatability. A typical reed-switch transmitter is accurate to ¼ in. whereas MTS is accurate to 1/16 in.,” he says.
Aiken cites the case of a chemical customer that uses a proprietary liquid that costs $1,000 per inch in the tank. “The high accuracy of our level transmitters provides better control of processes and inventory levels which leads to better asset optimization. This is achieved by only ordering inventory when necessary and by using the correct amount of consumables in a process. With such high costs, it is easy to see how using the high accuracy of MTS level transmitter keeps a company from wasting money,” declares Aiken.
Meanwhile, at Emerson the quest for accurate measurement while meeting ever more stringent health and safety regulations, reducing maintenance costs and improving reliability continues to drive the company to provide better performing instrumentation with more functionality at lower cost.
One of its latest developments is a rapid (3-ns.) solid-state switch for transmitting and receiving the radar signal in a GWR device. Named direct switch technology (DST), the system reportedly provides a measurement signal that’s many times stronger than that from traditional GWR devices. It is said to offer reliable measurement over long distances and with very low dielectric materials, even when using a single lead probe. Another advance is the use of a smart galvanic interface that increases the ability of the transmitter to handle electromagnetic interference, a common phenomenon in open tanks and plastic vessels.
Magnetrol International, Downers Grove, Ill., also is enhancing its lineup. Its Digital E3 Modulevel liquid level displacer transmitter features Foundation Fieldbus H1 communications prototcol. The new transmitter is said to deliver a range of benefits, including: lower installation and operating costs due to reduced need for cable, cable trays, conduits and associated hardware; interoperability across vendors; remote diagnostics; and highly reliable data transmission.
The company’s second new offering is the Model R82 radar transmitter for level and volume applications. The emphasis here is on improved cost-competitiveness; the device allows internal adjustment of beam orientation without removing the unit from the vessel, as well as HART-communication and PACTware capabilities.
For its part, Vega, Schiltach, Germany, used the ACHEMA trade show in May to showcase the next generation of its successful plics product concept. In plics plus, reduced complexity is the key. Features include simpler adjustment thanks to an enhanced indicating and adjustment module, pluggable terminal blocks and mechanical disassembly aids, plus low operating voltage and faster signal processing.
Seán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at firstname.lastname@example.org.