This article was printed in CONTROL's May 2009 edition.
As advances in digital signal processing and low-power operation circuits make their way into the design of field instruments, ultrasonic level transmitters have gotten smarter and more effective. Magnetrol’s new Echotel Model 355 is a case in point.
As Magnetrol’s ultrasonic level product manager, Mark Mackinnon describes it, “This transmitter can handle applications that were unthinkable just a few years ago. Take this one. A slightly agitated 10-foot tank with condensation, a slowly turning agitator and light foam. The Model 355 can handle it, where before now, this would not be recommended for ultrasonics.”
The onboard software analyzes the echo profile, compensates for temperature and rejects echoes from false targets. Then it processes the true echo from the liquid surface. “This is how we can get reliable measurement,” Mackinnon says, “even in tough applications.”
The 355 is FM-approved non-incendive and intrinsically safe and ATEX-approved intrinsically safe, non-incendive and explosion-proof. The 355 has been tested to EN 61326 and is in compliance with the EC EMC directive. It operates as a two-wire transmitter with a power consumption of less than 1 watt. It is available as either a conventional 4-20 mADC transmitter or with HART digital signal. The HART models can be configured and diagnosed using PACTware software from a remote PC or laptop. The 355 has an onboard, menu-driven, four-pushbutton, two-line-by-16-character LCD user interface.
With the PACTware software package, Mackinnon notes, “you can perform a complete configuration with the extra capability of capturing echo wave forms, viewing trend data, diagnostic conditions and all of the transmitter’s configuration parameters.”
The 355 is designed to operate as a level transmitter, a tank-volume transmitter or an open-channel flowmeter. It is programmed with most common tank shapes, most common flume or weir primary elements, and a generic open-channel flow equation. For unusual flow or volume applications, it also has a 20-point custom table for characterization. For flow and batching applications, the software has two 7-digit totalizers, one resettable and one not.
The 355 is available with a cast-aluminum housing and a Kynar Flex (PVDF) transducer or a Lexan polycarbonate housing with a polypropylene transducer. Both are designed for a 2-inch NPT process connection and are available with either two ¾-inch NPT or M20 conduit fittings.
“The 10-degree beam angle, which is narrower than most ultrasonic transmitters,” Mackinnon says, “allows the 355 to be used in applications where other units fail due to false reflections from obstructions in the tank.” This is critical, Mackinnon goes on, when working with smaller vessels. “At 5 feet, the beam’s radius is only 5.2 inches, and at 10 feet, it is 10.5 inches,” he says. “This lets us shoot between ladders and agitator shafts in even small-diameter vessels.”
Magnetrol has created an application design “calculator” so users can determine the maximum range in specific applications. This “calculator” is found on page 3 of the Model 355 product brochure. It takes into account operating parameters such as surface agitation, vapors and steam, beam-spread interference and foam on the liquid surface. Each parameter has several conditions, each of which has been assigned a performance multiplier. The designer simply takes the range of the transmitter and multiplies it by each of the “condition factors” that apply to that specific application, and the actual maximum operating range is determined. This increases the probability of a successful application.
“We’re making the Echotel 355 available on our ESP expedited shipping plan,” Mackinnon says. “This means we can ship within a week after we receive an order.”