An Instrument to Measure Servomechanism Performance

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Abstract
A transient recorder of the ``memory'' type for measuring transients applied to positioning servomechanisms is described in some detail. Essentially, the recorder consists of a bank of condensers, on which the transient voltages are successively impressed and later read off a CRO screen and plotted as a function of time to reveal the nature of the transient. In recording a transient, errors not exceeding ten percent are to be expected of the equipment. Rapidity of recording transients is one of the chief advantages of the system. Equipment for measuring the amplitude and phase response of a servomechanism, when subjected to an alternating input of variable frequency, is described. The measurement of the phases of input and output angles of a positioning servo is accomplished by means of a commutator driven by the sine wave generator, which supplies the alternating input to the servomechanism. The commutator has but one bar, and a vacuum tube voltmeter is connected to an angle‐measuring synchro, once each cycle, by a brush which may be moved to find the zero point of the modulated wave representing the alternating input. The phase angle between the input and output may be read as the difference between the angle positions of the brush used to locate the zero point of the modulated waves of the input and output. Phase angles may be measured with an error not exceeding one degree.

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