Rosemount Sues Ohmart/Vega Over Level Sensor Technology

Rosemount, Inc. (Eden Prairie, MN), a division of Emerson Electric Co., has filed a patent infringement suit against Ohmart/Vega Corp. (Cincinnati, OH) over two-wire radar level sensor technology. The company filed the suit on March 22, 2000, in the Federal Court in Wilmington, DE.

Rosemount charges thatUS Patent 6,014,100 (Two-wire RADAR sensor with intermittently operating circuitry components), issued on January 11, 2000, to Germany's Vega Grieshaber KG, one of Ohmart/Vega's two owners, infringes on its own US Patent 5,672,975 (Two-wire level transmitter). The patent covers technology used in a two-wire radar level sensor.

Level sensors work by directing a radar beam down to the material in a container. It then analyzes the amount of it takes to receive a reflected signal and container height to determine the level of the material inside.

Radar level sensors use significant amounts of power. In the past, they could not operate on the 4-20 mA two-wire system used to run loop controllers. Instead, they required a second set of wires for power. This adds to their cost and increases the opportunity for failure.

Rosemount's patent describes a microwave source and receiver that use low enough power to operate as a 4-20 mA two-wire system.

According to the Vega patent, the Rosemount patent does not disclose "how such low-power components could be obtained." As a result, it says, Rosemount's patent "appears to be based more on a theoretical than a practical solution."

In its patent, Vega contends that existing low-power semiconductor transmitters are too inefficient to produce a beam strong enough for accurate measurement using a two-wire power system.

Vega's solution is to link the transmitter to a process control loop and operate it intermittently. The unit's capacitors and accumulators collect and store power, then discharge it in a burst to operate the high or medium-powered microwave transmitter. The unit has high enough power to provide an accurate measurement.

Vega's patent references the Rosemount patent. It says the patent examiner granted the Vega patent because it is "different from and not derivable from Rosemount's patent."

Ohmart/VEGA believes the invention described in the Vega patent is the only workable two-wire radar solution. The company says it could become the dominant patent covering the technology.

"We find it interesting that Rosemount, who filed their patent in 1995 claiming to describe a workable 'two-wire' radar system, does not to my knowledge currently market a 'two-wire' radar level solution, even in the year 2000," says Ohmart/Vega president/CEO Joe Stigler.

"However, Rosemount is attempting to deny the marketplace an important, innovative and workable level solution that has thousands of successful installations."

"It is also interesting that Rosemount claims 'irreparable harm' by Ohmart/VEGA," Stigler continues. "We are a small company of approximately 110 people in the United States with sales volume of less than 1% of Rosemount's sales."

He says Ohmart/Vega is "very confident in a positive outcome."

For more information: Rosemount Inc., 12001 Technology Dr., Eden Prairie, MN 55344. Phone: 612-941-5560. Fax: 612-949-7001.

Or: Ohmart/Vega Corp., 4241 Allendorf Dr., Cincinnati, OH 45209. Phone: 513-272-0131. Fax: 513-272-0133.

By Alan S. Brown