Automotive tire pressure monitoring system or TPMS is an electronic system designed to monitor the air pressure inside the pneumatic tires on various types of vehicles. TPMS warns the driver about significant loss in tire inflation pressure through the use of a low tire pressure warning light on the instrument panel. Under-inflated tires affect the vehicle's handling and extend the stopping distance. Driving for long periods with under-inflated tires can also cause tire damage and increase fuel consumption.

How does a TPMS work?

A basic Automotive Tire Pressure Monitoring System installation consists of individual sensor units mounted on each wheel. The sensors measure the air pressure and temperature inside the tire and transmit this data via low-frequency radio signals to a central receiver unit. The receiver unit is connected to the vehicle's computer system. It processes signals from all the wheels, compares pressure readings to a preset threshold and triggers an alert if any tire is underinflated. Direct and indirect TPMS are the two main types based on how they monitor tire pressure.

Direct TPMS

Direct TPMS, also known as real-time TPMS, directly measures tire pressure using pressure sensors mounted on each wheel or tire assembly. The sensors have batteries that allow them to periodically transmit pressure readings to the vehicle's computer. When pressure differences are detected beyond the threshold limit, the driver is instantly notified through the low tire pressure warning light on the instrument panel. Direct systems provide real-time pressure readings without any initial calibration or resetting after tire rotation.

Indirect TPMS

Indirect or non-sensored TPMS do not have individual sensors installed on each wheel. Instead, it deduces pressure loss based on inputs from various existing electronic systems like the antilock braking system or electric stability control. Indirect TPMS monitors wheel speed, acceleration and other vehicle dynamics parameters. It compares deviations from normal rolling circumference to estimate under-inflation. Drivers need to reset the system after rotating tires to update wheel positions in memory.

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