TIRE INFLATION PRESSURE DETERMINING SYSTEM AND TIRE INFLATION PRESSURE DETERMINING APPARATUS

摘要

A measurement result is wirelessly transferred to the exterior without providing any highly precise oscillator circuit to an air pressure determining apparatus attached to a tire. An LC resonance circuit is constituted by a coil (Ls) and a pressure sensor (42) that varies in capacitance in accordance with a tire inflation pressure. The variation of the electromagnetic field of a frequency (f0) generated by a sensor control unit (10) is detected by use of a coil (L2). Based on this, a clock signal is generated, and then inputted to a coil (Le) transformer-coupled with the coil (Ls), thereby exiting the LC resonance circuit. An output voltage of the LC resonance circuit according to the intensity of the resonance is converted to digital data by an A/D converting circuit (50). The impedance of the coil (L2) is caused to vary in accordance with the bit string constituting that data. This causes, via the foregoing electromagnetic field, a modulation to occur in the voltage of a coil (L1) of the sensor control unit (10).