Apparatus and method for determining an engine speed

A removable sensor assembly for non-intrusively sensing the speed of an engine comprising a crankshaft, the removable sensor assembly comprising:

• a housing comprising a recess configured to removably receive and engage a portion of an item directly coupled to the crankshaft, wherein rotation of the crankshaft rotates the item;
• and
• a force sensing device received in the housing, the force sensing device being configured to wirelessly provide information indicative of angular motion of the crankshaft, the force sensing device comprising:
• a first coil, the first coil being configured into a ring;
• a second reference coil, the second coil being configured into a ring and being disposed within the first coil;
• a ring disposed between the first coil and the second coil, wherein the ring precludes a tensile force from being applied to the second reference coil;
• a power supply for providing an excitation to the first coil and the second coil, wherein the first coil provides a first signal and a second signal each corresponding to the movement of the housing, the first signal corresponding to the resistance of the first coil with respect to angular motion of the crankshaft and the second signal corresponding to the inductance of the first coil with respect to angular motion of the crankshaft and wherein the second coil provides a third signal and a fourth signal each corresponding to the movement of the housing, the third signal corresponding to the resistance with respect to angular motion of the crankshaft of the second coil and the fourth signal corresponding to the inductance of the second coil with respect to angular motion of the crankshaft;
• and
• a signal transmitter coupled to the coil to receive and transmit the first signal, the second signal, the third signal and the fourth signal.

A method for non-intrusively sensing instantaneous speed of an engine comprising a crankshaft having an end with an externally accessible bolt, the method comprising:

• affixing a sensor assembly to the externally accessible bolt, the sensor assembly comprising:
• a first coil, the first coil being configured into a ring;
• a second reference coil, the second coil being configured into a ring and being disposed within the first coil;
• a ring disposed between the first coil and the second coil, wherein the ring precludes a tensile force from being applied to the second reference coil;
• a power supply for providing an excitation to the first coil and the second coil, wherein the first coil provides a first signal and a second signal each corresponding to the movement of the housing, the first signal corresponding to the resistance of the first coil with respect to angular motion of the crankshaft and the second signal corresponding to the inductance of the first coil with respect to angular motion of the crankshaft and wherein the second coil provides a third signal and a fourth signal each corresponding to the movement of the housing, the third signal corresponding to the resistance of the second coil with respect to angular motion of the crankshaft and the fourth signal corresponding to the inductance of the second coil with respect to angular motion of the crankshaft;
• and
• a signal transmitter coupled to the first coil and the second coil, the signal transmitter being configured to receive and transmit the first signal, the second signal, the third signal and the fourth signal as an output signal, wherein the signal transmitter wirelessly transmits the output signal from the sensor assembly.