Flywheel Tooth Count
The flywheel tooth count is the number of pulses the magnetic pickup produces in one engine revolution and is the multiplier that converts pulse frequency into speed. Common values on engines are between 110 and 160 teeth. If the wrong tooth count is entered into the controller, the measured speed comes out wrong by the same ratio.
The relationship is simple: speed (rpm) = 60 × frequency (Hz) / tooth count. For example, on a flywheel with 118 teeth, 1500 rpm corresponds to a pulse frequency of 2950 Hz.
- The tooth count is obtained by counting on the flywheel itself or from the engine catalogue; it is not guessed.
- When a wrong value is entered the system appears fault-free but deviates by a constant ratio. If the display shows 1500 rpm while the alternator frequency is not 50 Hz, this is the first thing to suspect.
- The verification method is to compare with an independent tachometer or, on a 4-pole alternator, with a frequency measurement.
This concept comes up when a system that measures speed is set up. Because the standard GS740 kit has no speed reading, it has no tooth count parameter either; in scenarios that require measurement, the optional speed-reading module or a separate tachometer is used.
Context in which this term is used: Electronic speed and throttle control on diesel engines