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Mini linear sensors ensure correct positioning
of super-deep ice-coring system

Miniature LVDTs withstand drilling operations 2 miles deep into ice at temperatures below -30 degrees C.

Macro Sensors' miniature LVDT Linear Position Sensors serve as part of a steering actuator control system that regulates the tilt of a new Replicate Ice Coring System designed for a U.S. Deep Ice Coring Project currently being conducted in one of the snowiest regions of the West Antarctica Ice Sheet (WAIS) for studies of climate, ice sheet history, and cryobiology. The multi-year WAIS Divide project is examining approximately the last 100,000 years of the Earth's climate history by drilling and recovering a deep ice core from the ice divide in central West Antarctica.

Replicate Ice Coring System.

 

 

While an ice core 3,045 m into the ice sheet was recovered in December 2011, a Replicate Ice Coring System will re-enter the existing bore to extract additional ice related to areas of scientific interest. Using the electromechanical drill system, scientists hope to extract 250 m of new ice cores, going down to depths of about 4,000 m, to analyze different properties in the ice cores.

While initially following the course of the parent bore hole, the Replicate Ice Coring System will slightly alter its course to create a second path to collect ice samples. The drill of the Replicate Ice Core System uses two steering actuator sections to tilt itself in the parent borehole at a targeted trajectory. Located along the shaft of the drill, the actuators apply lateral pressure against the side of the borehole to alter the orientation of the drill head. The actuators tilt and guide the drill into the replicate borehole where ice samples are collected.

"The Replicate Ice Coring System is the first of its kind engineered with a steerable drill with the intention of retrieving additional samples of ice cores at targeted depths using an existing borehole," says Chris Gibson, lead mechanical engineer, Ice Drilling Design and Operations (IDDO) of Space Science and Engineering Center at the University of Wisconsin-Madison who is a member of the team that engineered the drill system.

Macro Sensors' LVDT CD 375 Series of 3/8-in. (9.5-mm) -diameter AC-operated LVDTs.

 

 

Six Macro Sensors CD Series Miniature LVDT Linear Position Sensors serve as part of the replicate actuator modules that push the drill out of the original hole at a targeted trajectory. Providing feedback on drill orientation, the AC-operated LVDT linear position sensors work as part of a closed-loop system, controlled by an onboard IC, with set points provided by an operator.

While the compact 3/8-in.-diameter size of Macro Sensors' Miniature LVDT Linear Position Sensors is ideal for the small space of the actuator system, the sensor's resistance to pressures up to 20 kpsi proves essential to withstand extreme forces present as the drill travels 2 miles deep into the ice at temperatures below -30 degrees C. To accommodate the high pressure, the LVDT sensor case is vented to equalize pressure inside and outside the LVDT linear position sensor.

"Macro Sensors' LVDT Linear Position Sensor is uniquely well suited to our application because of its pressure rating," says Gibson. "The drill is designed to operate at depths of 4,000 m (5,000 psi) in a fluid-filled bore hole."

First production deployment of the Replicate Ice Coring System is scheduled for December, with a full system test running next summer that simulates conditions a close as possible to those in the field. Module-level testing at pressure and temp is also being performed.

For more information on the West Antarctica Ice Sheet (WAIS), please refer to http://waisdivide.unh.edu/. For more information on Macro Sensors Miniature AC-operated LVDTs, please refer to the website at www.macrosensors.com/CD_375.html or contact the factory at: positionsensors@macrosensors.com.

Source: Macro Sensors

Published October 2012

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