David Jangraw

Summer 2006

Summer 2006: Capacitive Distance Probe
GE Global Research Center, Niskayuna NY

At GE I worked on a capacitive distance-measuring probe for use in the new GE-nx aircraft engine. As part of a team headed by James Simpson, I tested the current design, suggested improvements to the testing apparatus, and analyzed experimental data and ANSYS modeling results using MATLAB.


The purpose of the probe was to make the engine maximally efficient by allowing the turbine blades to be as close to the outer casing as possible. The size of the shroud can be changed, but the engine must know this distance to change it optimally. The smaller the space between blade and shroud, the more efficient the engine. Of course, allowing the blades to extend too far would cause collisions in the engine, and that’s a nasty health hazard. So the probe must be very reliable. The current method is to use computer modeling to estimate this distance, necessitating a bit of extra space to be safe.

The Challenge:

The probe would have to withstand the incredibly harsh conditions inside a jet engine: intense heat, constant vibration, and jet blades speeding past at incredible speeds. With these obstacles stacked against it, the probe still hoped to deliver distance measurements accurate to within 1/1000 of an inch.

The Probe Explained:

The team decided to make the probe a metal plate with a known current running through it. Each blade, for the brief moment when it got close enough, would form a capacitor, or charge-storage device, with the probe. With some smart designing of the probe and blades, reading the charge on this capacitor could allow accurate readings of the distance between probe and blade.


The probe was still in testing at the end of my internship, but things were looking good. To be safe, I will let the details of this project remain the property of GE.

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