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US Patent: 5,677,632
Automatic Calibration for a Capacitive Pickup Circuit
Patentee:
Michael B. Meeker (exact or similar names) - Kenosha, WI

USPTO Classifications:
324/380, 324/601

Tool Categories:

Assignees:
Snap-On Technologies, Inc. - Crystal Lake, IL

Manufacturer:
Not known to have been produced

Witnesses:
none listed

Patent Dates:
Applied: Feb. 27, 1995
Granted: Oct. 14, 1997

Patent Pictures:
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Report data errors or omissions to steward Stan Schulz
Snap-On Tools Company History
Description:
Emrich & Dithmar - patent attorneys

Abstract

A calibrating pickup circuit detects, using primary and secondary pickups, the primary and secondary voltages of an ignition coil of known turns ratio. The pickup circuit includes a programmable gain amplifier, responsive to the detected secondary voltage waveform signal and to a gain control feedback signal for generating an amplified secondary voltage waveform signal wherein the feedback signal has an initial predetermined value in calibration mode and has a calibration value in signal monitor mode. A waveform multiplexing circuit is selectively operable in calibration mode to alternately sample the primary and the amplified secondary voltage waveform signals over a predetermined period to generate a single interlaced waveform signal. Waveform comparison is then performed by evaluating the single interlaced waveform signal and a secondary-to-primary ratio calculated representative of the signal strength difference between analogous portions of the primary and the amplified secondary voltage waveform signals A calibration value is then determined on the basis of the secondary-to-primary ratio and the known turns ratio of the ignition coil.

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