D.C. machine as a relaxation oscillator and as a switch

The use of a d.c. machine as a low-frequency relaxation oscillator is described. The basic machine is a conventional shunt-excited generator to which has been added an inductor connected across brushes in electrical space quadrature with those required for shunt excitation. By adjustment of the inductor and field-winding circuit resistances, the polarity of the terminal voltage can be made to change either periodically or in response to a control signal, and hence astable, monostable or bistable operating conditions can be obtained. The theory of the oscillator is discussed and verified qualitatively by measurements on an experimental machine. Examples of the predicted waveforms and test results are included in the paper.