tachometer (or revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The type of sensing is dictated by the mechanism that is exploited for sensing engine speed:

  • Mechanical, this connection generally involves the use of a metal cable; this solution is used for both mechanical and magnetic tachometers.
  • Electronic, this connection relies on transmitting electrical pulses, usually from the crankshaft position sensor, and then transmitting them to the electronic tachometers. In vehicles with a distributor ignition system, the pulse is taken from one of the poles of the primary coil winding.
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