Masters Theses


"The purpose of this thesis is to illustrate the practicality of using an auxiliary servo system to shift parameters in damping networks of the main servo system.

Since amplification is most easily achieved with A.C. amplifiers and since A.C. servo motors are superior in operation to D.C. servo motors, because no brushes or commutators are needed, the A.C. servo system is widely used. However, one major problem is confronted when designing an A.C. servo system. This is the problem of designing damping circuits and compensating circuits which are insensitive to carrier frequency fluctuations. Notch filters provide the desired transfer functions, but they are sensitive to carrier frequency fluctuations. A notch filter is an electrical network that is resonated at the carrier frequency. The carrier frequency for A.C. systems is usually 60 or 400 cps. If the carrier frequency should drift from the desired value the notch filter will no longer be resonated at the carrier frequency. It has been suggested in a paper by Karl Schurr that an auxiliary servo system could be used to automatically vary parameters of the notch filter in the servo system to compensate for any fluctuations of the carrier frequency.

The need for such an auxiliary system is made apparent by visualizing the consequences upon the servo system if a fluctuation in the carrier frequency occurs. If such a fluctuation took place the notch filter would transmit a signal which would be amplified and cause the driving device of the system, usually a two phase motor, to change the position of the load. The error in position of the load that results may not be tolerated in many military installations, therefore, forcing the military to use D.C. servo systems.

The fact that stable frequency power supplies are not available for aircraft installations justifies the need for a research project to investigate the possibilities of finding a solution to this problem. Many articles have been written on improved techniques to design notch filters, but very little has been written on the problem discussed above.

The requirements of the auxiliary system to shift parameters of the notch filter in the main servo system depend upon two things; the carrier frequency power supply used, and the requirements of the main servo system. Consider first the carrier frequency power supply, which in an aircraft is usually an inverter. The inverter consists of a D.C. motor that drives an A.C. generator. If any fluctuations in the D.C. voltage occurs the speed of the D.C. motor changes causing a change in carrier frequency. The characteristics of the inverter as well as the regulation of the D.C. power supply to be used must be known. The auxiliary servo system must be able to compensate for any anticipated change of frequency due to the failure of the inverter to maintain a constant frequency output.

Such specifications as rise time, peak overshoot and settling time are determined primarily by the main servo system. The auxiliary servo system must respond more rapidly than the main servo system. The main servo will respond to an error fluctuation if the auxiliary system has a longer rise time.

In this paper a system is designed and analyzed and the results are compared to experimental results. The object of this paper is not to design an auxiliary system to meet a particular set of specifications, but rather to illustrate the practicality of such a system. Another purpose is to point out what parameters of the auxiliary system may be varied to meet a specific set of specifications"--Introduction, pages 8-10.


Nolte, Roger E.

Committee Member(s)

DeWoody, Robert T.
Erkiletian, Dickran Hagop, Jr.
Johnson, Charles A.


Electrical and Computer Engineering

Degree Name

M.S. in Electrical Engineering


Missouri School of Mines and Metallurgy

Publication Date



68 pages

Note about bibliography

Includes bibliographical references (page 67).


© 1960 Giles C. Sinkewiz, All rights reserved.

Document Type

Thesis - Open Access

File Type




Subject Headings

Servomechanisms -- Analysis
Feedback control systems -- Design
Electric power transmission -- Alternating current

Thesis Number

T 1249

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