Tachometer or other device to measure rpm; has metal disk mounted on axle placed in magnetic field parallel to axle, so that induced voltage between two sliding contacts can be measured to determine rotational velocity

摘要

When a metallic disk (1) rotates in a magnetic field (2) electrons are deflected. Use of sliding contacts (3,4) enables the voltage generated across the disk to be measured. The voltage is proportional to the rotational velocity and can be analyzed to determine rotational velocity.