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Design News, February 2013

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s e n s o r s / m ac h i n e v i s i o n DeSIGN aPPLICaTIONS Sensor Performance Key to Process Improvement Eddy current, non-contact displacement sensors are very different from the common inductive proximity sensor and can provide sub micron resolution in harsh environments. by Dan SPohn, Kaman PrecISIon ProDuctS C Consumer demand for higher quality and lower cost has driven improvements in automated manufacturing. Semiconductor manufacturing is a prime example where precision position feedback is critical to product quality, and the speed of processing is critical to cost. The level of technology integration the semiconductor industry utilizes is finding its way into nearly every automated manufacturing process regardless of the cleanliness of the environment or the end product being manufactured. Eddy current, non-contact displacement sensors Synchronous demodulator Coarse linearity adjust Zero adjust Target imity sensors typically employ a colpitts oscillator circuit, eddy current displacement sensors use a fixed frequency crystal oscillator and bridge circuit, creating a variable impedance transducer. The bridge is tuned to be in balance with the wire wound coil located in the probe. The coil is typically excited with 1MHz RF. The resulting oscillating electromagnetic field induces eddy current in any electrically conductive material — or target — that enters the field. The induced eddy current produces a corresponding electromagnetic field, which reacts with the probe field, causing an impedance change Fine Log AMP in the probe circuit. The linearity converter resulting bridge imbalance adjust is linearized and amplified, producing an analog Output voltage or current output Gain amplifier proportional to the distance adjust between the probe and the target. figure 1. automated manufacturing applications. can provide sub micron resolution in harsh environments, as well as in the sterility of a semiconductor clean room. how they Work Eddy current sensors are very different from the common inductive proximity sensor. Where prox- measurement Unlike an inductive proximity sensor, eddy current technology provides a linearized analog output proportional to the distance from the sensor tip to the target. When referencing from the fixed sensor position, dimensions can be determined. In progressive die-stamping operations accurate dimensioning of such things as boss height and bend angle can be determined. T16 Tre nd waT c h : sens o r s / m a c hi n e v i s i o n / a s u p p l e me nT To de s ign ne ws f eb r uary 2013 [www.designnews .com]

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