Shaft A of the tachometer is driven by the shaft whose speed is
to be measured. Mounted on shaft A is a commutator consisting
of two cylinders, Г and 1", insulated from each other, which
are contacted by brushes 3 and 4. The com mutator is connected
into a circuit inclu ding power source E, magnetoelectric receiver
V and capacitor C. When the com mutator rotates, brush 2
connects capacitor С alternately to battery E (when brush 2 contacts
cylinder 1') from which the capacitor is charged, and then
to receiver V (when brush 2 contacts cylinder 1"), to which the
charge is transm itted as a current pulse. The deflection of the
hand of the instrument is proportional to the number of pulses
per u n it tim e or to the speed (rpm) of the shaft being tested.
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