Alarm device for informing reduction of pneumatic pressure of vehicle

Abstract

An alarm device for signalling a reduction of pneumatic vehicle tire pressure comprises an oscillator 6 having an oscillation coil secured to a chassis of a vehicle; and a resonator 1 secured to the peripheral portion of a wheel having a tire adjacent to the oscillation coil and consisting of a pressure switch 4 for sensing an abnormal tire pressure change and a resonance coil and a capacitor 5 tuned to an electromagnetic wave radiated from the oscillation coil. A signal processing device contains a means for sensing a change in an oscillation condition generated in the oscillator due to a resonant condition of the resonator switched on and off in accordance with abnormal internal tire pressure and for processing a signal from the sensing means; and an alarm for generating a warning signal in accordance with the output of the signal processing device. The latter comprises a signal input section 21 having a desired number of input terminals, a signal processing section 22 having an arithmetic circuit connected to the signal input section, a resettable latch circuit 30,32, and an alarm section 23 operated by the output of the latch circuit whereby an alarm signal is not generated at normal internal pressure and during stops of the vehicle.