TACHOMETER SYSTEM INCLUDING AN RF SIGNAL MODULATOR AND DETECTOR

• US 3,611,138 A
• Filed: 03/05/1970
• Issued: 10/05/1971
• Est. Priority Date: 03/05/1970
• Status: Expired due to Term

• Current Assignee: Gary L. Winebrener
• Original Assignee: Gary L. Winebrener
• Inventors: Winebrener, Gary L.
• Primary Examiner(s): Lynch, Michael J.
• Application Number:
  US05/016,809
• Time in Patent Office: 579 Days
• Field of Search: 324/166,173,174,175,34SC,161 317/5 318/52,231 73/229-231 332/56
• US Class Current: 324/173
• CPC Class Codes: G01P 3/4802 by using electronic circuits in general

Abstract

A tachometer system for detecting the speed of rotation of a rotating member. In this tachometer system, an LC tank circuit is excited by an RF signal. The inductance of the coil incorporated in the LC tank circuit is varied in accordance with the rotation of the rotating member and, accordingly, an amplitude modulated RF signal is developed across the tank circuit in response to rotation of the rotating member. This modulation is doubled in amplitude and detected to provide a signal whose frequency is related to the speed of rotation of the rotating member.

Claims

1. An electrical tachometer for providing a signal which is indicative of the speed of rotation of a rotating member, comprising:

an RF signal source, a tank circuit comprised of parallel connected capacitive and inductive circuit elements coupled to said RF signal source, means driven by said rotating member and coupled to one of said circuit elements of said tank circuit for varying the impedance of said tank circuit at the frequency of said RF source as a function of the speed of rotation of said rotating member whereby, said tank circuit provides an amplitude modulated signal whose modulation envelope has a frequency which is a function of the speed of rotation of said rotating member, an electrical circuit coupled to said tank circuit for developing an amplitude modulated signal in which the amplitude of the modulation envelope is substantially twice the amplitude of the modulation envelope developed in said tank circuit, said electrical circuit comprising a capacitor and a transistor having a collector, emitter and base, means connecting said capacitor serially with the base-emitter circuit of said transistor across said tank circuit, means connecting the collector-base circuit of said transistor across said tank circuit, the base-emitter circuit of said transistor being periodically reverse biased and driven conductive in a reverse direction by the signal applied to the base-emitter circuit of said transistor from said tank circuit, and a detector coupled to said transistor for providing a signal the frequency of which is a function of the speed of rotation of said rotating member.

2. An electrical tachometer for providing a signal which is indicative of the speed of rotation of a rotating member, comprising:

an RF signal source, a tank circuit comprised of parallel connected capacitive and inductive circuit elements coupled to said RF signal source, means driven by said rotating member and coupled to one of said circuit elements of said tank circuit for varying the impedance of said tank circuit at the frequency of said RF source as a function of the speed of rotation of said rotating member whereby, said tank circuit provides an amplitude modulated signal whose modulation envelope has a frequency which is a function of the speed of rotation of said rotating member, an electrical circuit coupled to said tank circuit for developing an amplitude modulated signal in which the amplitude of the modulation envelope is substantially twice the amplitude of the modulation envelope developed in said tank circuit, said electrical circuit comprising a capacitor, a Zener diode, a diode and a transistor having a collector, emitter and base, means connecting said diode and Zener diode in series across the base-emitter circuit of said transistor with the cathode of said diode connected to the base of said transistor and with the cathode of said Zener diode connected to the emitter of said transistor, means connecting said capacitor serially with the parallel combination of said diodes and the base-emitter circuit of said transistor across said tank circuit, means connecting the collector-base circuit of said transistor across said tank circuit, the breakdown voltage of said Zener diode being less than the reverse breakdown voltage of the base-emitter junction of said transistOr whereby, the signal applied to said electrical circuit from said tank circuit periodically drives said Zener diode conductive, and a detector coupled to said transistor for providing a signal the frequency of which is a function of the speed of rotation of the rotating member.

3. An electrical tachometer for providing a signal which is indicative of the speed of rotation of a rotating member, comprising:

an RF signal source, a two terminal LC tank circuit, said LC tank circuit comprising a parallel connected sensing coil and capacitor, a transistor having a base, an emitter, and a collector, means connecting said RF signal source across said base and emitter of said transistor, means connecting said collector of said transistor with a first terminal of said LC tank circuit, a bypass capacitor connecting the second terminal of said LC tank circuit to said emitter of said transistor, a source of direct current, means connecting said source of direct current between said emitter and said second terminal of said LC tank circuit whereby, said transistor is controlled in accordance with said RF signal source and an RF signal is developed across said LC circuit, means driven by said rotating member for causing the inductance of said sensing coil to vary in accordance with the rotation of said rotating member whereby, the RF signal developed across said LC tank circuit is amplitude modulated, a clamping circuit including a capacitor and a Zener diode coupled to said LC tank circuit for providing an amplitude modulated output signal wherein the amplitude of the modulation envelope is substantially twice that supplied by said tank circuit, and a detector coupled to said clamping circuit for providing a signal the frequency of which is a function of the speed of rotation of said rotating member.

4. An electrical tachometer for providing a signal which is indicative of the speed of rotation of a rotating member, comprising:

a two terminal LC tank circuit, said LC tank circuit comprising a parallel connected sensing coil and capacitor, a first transistor having a base, an emitter, and a collector, means connecting said collector of said first transistor to a first terminal of said LC tank circuit, a bypass capacitor connecting the second terminal of said LC tank circuit with said emitter of said first transistor, an RF signal source, means connecting said RF signal across the base and emitter of said first transistor, a source of direct current, means connecting said source of direct current between said emitter of said first transistor and said second terminal of said LC tank circuit whereby, said transistor is controlled in accordance with said RF signal source and an RF signal is developed across said LC tank circuit, a metallic wheel having circumferentially disposed alternate teeth and notches driven by said rotating member, said metallic wheel rotating in close proximity to said sensing coil of said LC tank circuit to thereby cause the inductance thereof to vary in accordance with the rotation of said rotating wheel whereby, the RF signal developed across said LC tank circuit is amplitude modulated, amplitude modulation doubling means coupled to said LC tank circuit for providing an output signal wherein the amplitude of the modulation envelope is substantially twice that provided by said tank circuit, said doubling means comprising a capacitor and a second transistor having a base, an emitter, and a collector, means connecting said capacitor serially with the base-emitter circuit of said second transistor across said LC tank circuit, means connecting the collector-base circuit of said second transistor across said LC tank circuit, the base-emitter emitter circuit of said second transistor being periodically reverse biased and driven conductive in a reverse direction by the signal applied To said second transistor from said LC tank circuit, and a detector coupled to said second transistor for providing a signal the frequency of which is a function of the speed of rotation of said rotating member.