Patent attributes
A tachometer used to measure a speed of an engine. The tachometer includes a pickup, a counter circuit, a conversion circuit, an automatic switching device, an indicator and a meter display. The inductive pickup may be disposed around a spark plug wire of the engine to generate a pulse signal in response to a current flowing through the spark plug wire. The pulse signals are then counted by the counter circuit and input to the conversion circuit therefrom. The conversion circuit typically includes a plurality of lookup tables, each having mapped information correlating the pulse signals to the engine speed for a particular number of engine cylinders. The automatic switching device is operative to call up alternate lookup tables, e.g. each time when the electrical system of the engine is turned on. The display may be display the number of engine cylinders called up by the automatic switching device and measured engine speed.
