Abstract

In the present article are described the detailed construction and various examples of applications of the “Ultramicrometer,” a new instrument for measuring a small displacement or motion utilizing a generating valve circuit. In its usual form the instrument consists of a tuned grid circuit, but it can easily be changed to the Colpitts-Hartley circuit. The displacement or motion to be measured is made to produce either a change in the capacity in the circuit or a change in the eddy-current loss, and in consequence a corresponding change in the anode current of the valve results. This change in the anode current is measured with a galvanometer, or if a permanent record is needed, an Einthoven string galvanometer or a Duddell oscillograph is employed. The anode current itself is balanced by means of a potentiometer method, or a small transformer is inserted in the anode circuit.

With this instrument the capacity method as well as the eddy current method may be carried out, and the anode current may be balanced or a transformer may be inserted according to the kind of problem; all the necessary resistances and transformer being contained in the instrument.

As the examples of application of the instrument are described the recording of earthmovements, direct recording of accelerations, an electrical indicator for high speed internal combustion engines, precise recording of sounds, pressure variations and various mechanical vibrations.

© 1928 Optical Society of America

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