Fine Wire Sensors
Improve Position Measurement Systems

Eddy current measuring systems using fine wire sensors are being developed and used to accurately measure and assemble microchips and computer parts, aid in physics research, and even to monitor the noise and vibration levels of rocket engines. The components are gradually replacing measurement tools such as calipers, dial indicators and even micrometers.

The most critical component in eddy current measurement systems is the sensor, which is made from custom-designed coiled wire. When a high frequency oscillating current is directed through the coil, a varying electro-magnetic field surrounds it. When the sensor is placed close to a conductive target (the object being measured, monitored, or fabricated), the impedance of the sensor coil is changed. This change produces a signal that can be used by PCs or automated fabrication equipment to precisely define the position of the target in relation to the sensor.

Being at the heart of the measuring system, the quality of the wire used in sensor construction must be absolutely consistent from sensor to sensor and batch to batch. Kaman Instrumentation, a manufacturer of non-contact measuring systems, comments that they use a wide array of wire from copper to gold, in sizes ranging from 30 gauge down to a few thousandths of an inch. They eventually selected California Fine Wire to provide their wire stock, because of CFW's ability to customize orders.

A recent example required a system designed to measure the velocity of .50 caliber munitions. The lab performing the testing selected eddy current technology in an effort to eliminate inaccuracies found with traditional "break wire" and "break paper" measurement systems. The dual sensor system that Kaman developed has hollow circular sensors placed an exact distance apart, with the round passing through their centers. The system can sense projectile speeds in excess of 3000 feet per second.

-- RM

For more information, contact:

California Fine Wire Co., PO Box 446, Grover Beach, CA 93483-0446. 805-489-5144. Circle 576.

Kaman Instrumentation, 1500 Garden of the Gods Road, Colorado Springs, CO 80907. 719-599-1873. Circle 577.