Abstract: A system for measuring the pressure of air in the tires of a moving vehicle including a wheel mounted transducer, a chassis mounted sensor, and a chassis mounted electronic processing unit for converting sensor signals to tire pressure indications. The transducer includes two fixed magnetic elements and a movable magnetic element positioned between the fixed elements. Tire air pressure moves the movable element against a spring so that its position indicates the pressure. The sensor generates a signal each time a magnetic element passes by it and these signals are coupled to the processing unit. The processing unit measures the time intervals between the passage of the first and second fixed element and calculates pressure from the ratio of time periods. The ratio makes the pressure calculation independent of vehicle speed. The processing unit also multiplexes the outputs of multiple sensors to provide sequential readout of tire pressures and locations.