Pneumatic detection apparatus for a tire which utilizes pressure-sensitive displacement of an internal magnet

摘要

A magnetic-flux change-generating device 2 causes amplitude modulation of alternating magnetic flux in accordance with displacement of a movable body, and an amplitude-compensating device (low-pass filter) 4 causes attenuation of amplitude of electromagnetic-induction voltage of a pickup coil 3 substantially proportionally to frequency. When frequency of the alternating magnetic flux (also termed "carrier frequency") fluctuates, the amplitude of the electromagnetic-induction voltage fluctuates in proportion to the frequency, but because the amplitude of the electromagnetic-induction voltage is caused to be attenuated at an attenuation rate which is substantially proportional to the frequency, displacement can be detected accurately by this amplitude change, irrespective of change in the frequency of the alternating magnetic flux (i.e., the carrier frequency of the electromagnetic-induction voltage).