Constant amplitude control of electromechanical oscillators

• US 4,177,434 A
• Filed: 05/30/1978
• Issued: 12/04/1979
• Est. Priority Date: 05/30/1978
• Status: Expired due to Term

• Current Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Ida, Edward S.
• Primary Examiner(s): Grimm, Siegfried H.
• Assistant Examiner(s): Westin, Edward P.
• Application Number:
  US05/910,849
• Time in Patent Office: 553 Days
• Field of Search: 331/116 M, 331/154, 331/156, 331/157, 331/155, 331/183, 331/25, 331/27, 318/114, 318/116, 318/118, 318/128, 318/130, 318/132, 310/25, 310/26, 310/27, 310/37, 73/646, 73/647, 73/648, 73/54, 73/59, 73/DIG. 1, 73/DIG. 2, 73/32 A, 73/579, 332/3, 58/23 AC, 58/23 TF, 58/23 V
• US Class Current: 331/27
• CPC Class Codes: H03L 5/00 Automatic control of voltage, current, or power

Abstract

Method and system for the constant amplitude control of an electromechanical oscillator utilizing a phase locked oscillator to generate a secondary a-c setpoint which is compared to the oscillator output to provide a difference signal which is passed as a fast-acting negative feedback signal to stabilize the amplitude.

Claims

1. A method for maintaining the amplitude of an electromechanical oscillator mechanical output signal constant independent of its operating frequency, comprising the steps of:

generating a constant amplitude a-c signal in phase agreement with said output signal;

developing a d-c signal related to said output signal amplitude;

continuously integrating the difference in voltages between said d-c signal and a preselected setpoint voltage value to provide a control signal;

amplitude modulating said constant amplitude a-c signal with said control signal to provide a modulated a-c signal in phase with said output signal to maintain said oscillator in oscillation; and

maintaining the amplitude of said output signal in accordance with the algebraic sum of a linear negative feedback signal derived from said output signal and said modulated a-c signal, thereby to maintain said output signal amplitude constant.

2. An electromechanical oscillatory system providing a constant amplitude mechanical output signal independent of its operating frequency, said system having an input drive and an output and comprising:

a phase-locked loop circuit connected to the output of said system generating a constant amplitude a-c signal;

an amplitude detector coupled to the output of said system producing a time-varying d-c signal tracking said output signal;

an integrator connected to the output of said detector integrating the difference between said time-varying d-c signal and a preselected setpoint signal;

a modulator means connected to the output terminal of said integrator for modulating said a-c signal as a function of the magnitude of said integrated d-c signal to provide a modulated a-c signal in phase with said output signal to maintain said oscillator in oscillation; and

a summing junction coupled to the outputs of said system for summing a linear negative feedback signal derived from said output and said modulator means to provide a drive control signal as feedback to said system in accordance with the magnitude of the difference between said modulated a-c signal and said negative feedback signal.

3. The system of claim 2 wherein said system is a torsional oscillatory viscometer probe and includes attenuator means for adjusting the amplitude of oscillation of said probe.

4. The system of claim 2 wherein said modulator means is a photo conductor.

5. The system of claim 2 wherein said detector comprises a low-pass filter circuit connected in series with a precision a-c detector.