AMPLITUDE STABILIZED OSCILLATOR

• US 3,784,930 A
• Filed: 07/06/1972
• Issued: 01/08/1974
• Est. Priority Date: 07/06/1972
• Status: Expired due to Term

• Current Assignee: Alan J. Werner Jr, Robert E. Vosteen
• Original Assignee: Alan J. Werner Jr, Robert E. Vosteen
• Inventors: Vosteen, Robert E., Werner, Alan J. Jr.
• Primary Examiner(s): Duggan, D. F.
• Application Number:
  US05/269,454
• Time in Patent Office: 551 Days
• Field of Search: 331/141,116,116M,34,183,146,109 307/311 318/128-132,127 322/21
• US Class Current: 331/183
• CPC Class Codes: G01R 29/24 Arrangements for measuring quantities of charge
• CPC Class Codes: G01R 5/28 Electrostatic instruments
• CPC Class Codes: H03B 5/30 with frequency-determining element being electromechanical resonator
• CPC Class Codes: H03L 5/00 Automatic control of voltage, current, or power

Abstract

An electrometer apparatus having an amplitude stabilized oscillator circuit with an electromechanical resonant transducer connected to the input of the oscillator active stage. The transducer has first and second terminals. A differentially connected operational amplifier is also provided having plus and minus inputs, the first terminal of the electromechanical resonant transducer being connected to the plus terminal of the operational amplifier, and the second terminal being connected to ground. A light emitting source is connected between the output of the operational amplifier and ground, and is responsive to the output of the operational amplifier to supply a corresponding amount of energy to a light responsive element connected to the output of the operational amplifier. A negative feedback path connected between the light responsive element and the minus terminal of the operational amplifier is also provided. The electrometer may be used to measure unknowns such as the electrostatic potential of a surface in non-contacting manner or an electrostatic field.

Claims

1. An amplitude stabilized oscillator circuit comprising:

an electromechanical resonant transducer having first and second terminals, a differentially connected operational amplifier having plus and minus inputs, the first terminal of the electromechanical resonant transducer being connected to the plus terminal of the operational amplifier, the second terminal being connected to ground, a light emitting source connected between the output of the operational amplifier and ground, and responsive to the output of the operational amplifier to supply a corresponding amount of energy to a light responsive element connected to the output of the operational amplifier, and a negative feedback connection connected between the light responsive element and the minus terminal of the operational amplifier.

2. An amplitude stabilized oscillator circuit as recited in claim 1 wherein the light emitting source comprises a full-wave rectifier network and a light emitting device driven thereby.

3. An amplitude stabilized oscillator circuit as recited in claim 2 wherein the light responsive element and the transducer are connected with passive resistance elements to form opposite arms of a bridge network.

4. An amplitude stabilized oscillator circuit as recited in claim 2 wherein the full-wave rectifier network comprises a diode bridge network feeding a light emitting device comprising the series connection of a light emitting diode and a zener diode.

5. An amplitude stabilized oscillator circuit as recited in claim 3 wherein the full-wave rectifier network comprises a diode bridge network feeding a light emitting device comprising the series connection of a light emitting diode and a zener diode.

6. An amplitude stabilized oscillator circuit as recited in claim 5 wherein the light responsive element comprises a photoconductive device.

7. An amplitude stabilized oscillator circuit as recited in claim 6 wherein the transducer comprises a magnetic transducer.

8. An amplitude stabilized oscillator circuit as recited in claim 1 wherein the light responsive element comprises a photoconductive device.

9. An amplitude stabilized oscillator circuit as recited in claim 1 further comprising a single, grounded coaxial shielded lead connecting the transducer to the operational amplifier.

10. In an electrometer apparatus to measure unknowns such as the electrostatic potential of a surface in noncontacting manner Or an electrostatic field, having a capacitive detector positionable in electrostatic coupling relationship with the surface or in the electrostatic field to produce a detector signal representative of the magnitude and polarity of the unknown being measured for long-term static measurement, the improvement comrising:

an electromechanical resonant transducer having first and second terminals, operative to vibrate the capacitive detector at a predetermined frequency to vary the coupling relationship and produce modulated detector signals having a carrier frequency equal to the predetermined frequency, an amplitude stabilized reference oscillator circuit to produce reference signals at the predetermined frequency, a differentially connected operational amplifier having plus and minus inputs, the first terminal of the electromechanical resonant transducer being connected to the plus terminal of the operational amplifier, the second terminal being connected to ground, a light emitting source connected between the output of the operational amplifier and ground, and responsive to the output of the operational amplifier to supply a corresponding amount of energy to a light responsive element connected to the output of the operational amplifier, a negative feedback connection connected between the light responsive element and the minus terminal of the operational amplifier, and a detector connected to receive the reference signals and modulated detector signals at a fixed phase relationship to demodulate the latter and produce an output signal indicative of the magnitude and polarity of the unknown being measured.

11. The electrometer apparatus recited in claim 10 further comprising a wide ban, non-inverting voltage follower connected to the output of the detector having an operational amplifier and a photoelectric network connected to pass a frequency range wider than the carrier frequency.

12. The electrometer apparatus recited in claim 10 further comprising a wide band, non-inverting voltage follower connected to the output of the detector.