“The market for microwave [radar] and ultrasonic level transmitters continues its rapid growth across an expanding application base, thanks to their proven reliability and low maintenance requirements. Meanwhile, differential transmitter level systems benefit from better system construction, sizing and installation practices, giving increased installed reliability, while point level switches are widely used to meet safety standards for high/overfill and low level measurements,” notes Chettle. He expects further developments in enhanced instrument diagnostics to enable remote interrogation of instrument condition and advance warning of potential problems.
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.