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Non-Invasive Level Sensor Sees Through Film

July 30, 2003
Turck's Next-Generation Levelprox

Ultrasonic sensing technology has become a key method for detecting level in tanks where intrusion into the tank is not desired. It's a good solution when the material being measured is caustic or volatile, under high pressure, at very high temperatures, or the environment is sanitary.

Using ultrasonic devices to sense through the metal tank walls also renders moot material compatibility issues, since there is no direct contact with the media. Further, these units are not affected by stirring devices. Perhaps the only catch has been in applications involving high-viscosity media, such as yogurt or ketchup, which form a film inside the container wall that can throw off ultrasonic sensors.

To address this shortcoming, Turck developed a new version of its Levelprox line of level measurement systems. The dual-mode version features Echo Mode, an addition to the reverberation technology of the original sensor. In normal mode, this sensor determines the level of the media by evaluating the amplitude of the signal resonating inside the tank, just as the earlier generation of Levelprox units did.

The new Levelprox is being marketed both to end users and to OEM machine builders. The latter are incorporating it in equipment destined for breweries, dairies, food or beverage production facilities, wastewater treatment, chemical handling, and pharmaceutical applications.

"We're seeing a fair amount of interest from the OEM market," says Richard Tallant, Turck project application engineer, "especially for food and pharmaceutical applications, where its non-intrusive nature helps ensures the purity of the product."

Whereas film and other residue on the side of the tank can distort the resonance, and thereby throw off the earlier generation Levelprox sensor, Echo Mode allows the sensor to also factor in the echo as it returns from the opposite tank wall. Using both readings, an accurate level measurement can be determined.

By changing the dip-switch setting, the user will be able to select the appropriate operating mode for the application. But the unit also has the intelligence to know when it gets a bad reading, and it will take its own reading in Echo Mode.

Levelprox sensors are constructed of high-grade 316L stainless steel and can sense through walls 1-15 mm (0.04-0.59) thick. A 1½-in. Tri-clamp fitting is incorporated into the sensor and can be used with the optional mounting kit, which includes the clamp. The mount is welded to the tank, and the sensor is fastened to the mount with the Tri-clamp. This positions the sensor face in the ideal detection position and ensures a sanitary, leak-proof fitting. Levelprox is completely self-contained with no need for an additional amplifier.

A beta unit was tested in an OEM application for machinery that prepares pig heart valves for transplantation into humans. "There is a machine that flushes and sterilizes the valves," Tallant says. "The user must be sure the machine's chamber is properly filled with sterilant. The new Levelprox verifies that in a non-intrusive way."

With the Levelprox, no contaminants can be introduced to the system and there are no crevices for bacteria to hide in and multiply.

Levelprox largely opened a market for non-invasive level measurement when it was introduced last July, says Grant Bistram, marketing services manager. He says the new version should broaden the potential market.

For more information call 800/544-7769 or browse to


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