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AC Coupled Optical Digital Tachometer

IP.com Disclosure Number: IPCOM000087487D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Richards, LD: AUTHOR

Abstract

This device minimizes DC to low-frequency components in the output signal from an optical digital tachometer. The DC-to-low-frequency components of the tachometer output analog signal result in the output of asymmetrical pulses, when a conventional threshold detection technique is used.

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AC Coupled Optical Digital Tachometer

This device minimizes DC to low-frequency components in the output signal from an optical digital tachometer. The DC-to-low-frequency components of the tachometer output analog signal result in the output of asymmetrical pulses, when a conventional threshold detection technique is used.

Fig. 1 shows a circuit configuration which eliminates the DC-to-low-frequency component from the output signal of an optical tachometer. Essentially high-pass filter network 10 is connected in tandem with an amplifier 12 and zero-crossing detection comparator circuit 14. As the tachometer disk (not shown) rotates, an analog signal which is the result of interference created by the window's position on the disk and the mask is emitted. The analog signal is collected via phototransistor 16 and fed into high-pass filter network 10. The high-pass filter network filters out the undesirable component of the analog signal. The signal is then amplified and fed into a zero-crossing detection comparator circuit 14, which emits a symmetrical output signal at output terminal 18.

Fig. 2 depicts the analog signal after the undesirable components are filtered out. Fig. 3 depicts the symmetrical output pulses. If a constant asymmetrical pulse is desired, an adjustable threshold can be implemented in the circuitry of Fig. 1.

Fig. 4 shows the two frequency components of the digital tachometer analog input signal, while Fig. 5 depicts the resultant asymmetrical...