TIRE INFLATION PRESSURE DETERMINING APPARATUS

摘要

A tire inflation pressure determining system is provided in which measurement results are transmitted to the exterior without providing a high precision oscillation circuit to a tire-mounted air pressure determining system. An LC resonance circuit is composed of a coil Ls and an inflation pressure sensor (42) in which the electric capacitance varies in accordance with tire air pressure. The fluctuations of the electromagnetic field having a frequency f0 generated by a sensor control unit (10) are sensed in a coil L2, a clock is generated based on the sensed fluctuations, the clock is inputted to a coil Le that is transformer coupled to the coil Ls, and the LC resonance circuit is excited. The output voltage of the LC resonance circuit is converted to digital data in an A/D conversion circuit (50) in correspondence with the intensity of the resonance, the impedance of the coil L2 is varied in accordance with the bit sequence constituting the data, and a modulation is thereby generated in the voltage of a coil L1 of the sensor control unit (10) via the electromagnetic field.