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Measuring Moment of Inertia

IP.com Disclosure Number: IPCOM000074993D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Taylor, NB: AUTHOR

Abstract

The device includes a table 2 mounted on a shaft 3 for rotation about a vertical axis. A spring 4 applies torque to shaft 3 to give table 2 an angular acceleration. An emitter disc 5 also mounted on shaft 3 has slots 6 formed therein. At one side of emitter disc 5 is a lamp 7 and confronting the opposite surface of the emitter disc is a phototransistor 8. The output of phototransistor 8 is received by amplifier 9 which delivers an output to electronic counter 10. Projecting element 12 presents an upper edge 13 which serves as an aligning reference with respect to a mark, such as 14, on table 2.

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Measuring Moment of Inertia

The device includes a table 2 mounted on a shaft 3 for rotation about a vertical axis. A spring 4 applies torque to shaft 3 to give table 2 an angular acceleration. An emitter disc 5 also mounted on shaft 3 has slots 6 formed therein. At one side of emitter disc 5 is a lamp 7 and confronting the opposite surface of the emitter disc is a phototransistor 8. The output of phototransistor 8 is received by amplifier 9 which delivers an output to electronic counter 10. Projecting element 12 presents an upper edge 13 which serves as an aligning reference with respect to a mark, such as 14, on table 2.

During operation, table 2 is rotated to a fixed position and released. Spring 4 accelerates table 2 through about 300 degrees of rotation, whereupon the time interval between the emitter pulses generated by the emitter disc slots 6 is measured by timer 10. This measured interval corresponds to a value of inertia.

To calibrate the device, inertias of known value are tested and the time between emitter pulses recorded. The inertia of an unknown part is found by placing the desired axis over the center of table 2.

The table is then rotated through the controlled angular traverse and the elapsed time between emitter pulses observed. This value of elapsed time measurement is converted to a value of inertia by interpolation with known values.

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