Tire Inflation Pressure Monitor System (TPMS) is an electronic system designed to monitor the air pressure inside the pneumatic tires of vehicles. Low inflation tires are potentially dangerous, especially if a vehicle is heavily loaded and traveling at highway speeds during hot weather. The TPMS system is also called as tire-pressure indication system (TPIS). Tire-pressure monitoring system (TPMS) reports real-time tire-pressure information to the driver of the vehicle, either via a gauge, a pictogram display, or a simple low-pressure warning light. TPMS is an important vehicle safety system especially for heavy-duty vehicles such as trucks, buses, lorry, etc.

Direct Tire-Pressure Monitoring System (TPMS)

Direct Tire-Pressure Monitoring Systems (TPMS) employ physical pressure sensors inside or outside each tire and a means of processing and transmitting that information to the vehicle’s instrument cluster. Direct-sensor TPMS are specifically designed to cope with ambient and road-to-tire friction-based temperature changes, both of which heat up the tire, and increase its pressure. The alarm-activation threshold pressures are usually set according to the manufacturers recommended “cold placard inflation pressures”.

The Tire-Pressure Monitoring System to transfer sensor data from a rotating wheel, a direct-sensor system may use a radio-frequency (RF) wireless communication channel or electromagnetic coupling to overcome the tire/chassis rotational boundary.

Indirect Tire-Pressure Monitoring System (TPMS)

Indirect TPMS do not use physical pressure sensors. Indirect TPMS measure the “apparent” air pressure, by monitoring individual wheel rotational speeds, and other signals available outside the tire itself. Most indirect TPMS use the fact that an under-inflated tire has a slightly smaller diameter than a correctly inflated tire and therefore has to rotate at a higher angular velocity to cover the same distance as a correctly inflated tire.

Indirect Tire-Pressure Monitoring Systems (TPMS) are realized in software in combination with wheel-speed sensors for anti-lock braking systems, and electronic stability control systems. An advantage of the indirect TPMS is that it needs no sensors thus decreasing weight and cost as well as increasing customer satisfaction because sensor-related problems are eliminated. A disadvantage of indirect TPMS is that the driver must calibrate the system by pushing a reset button on the dashboard via an on-board computer and if this is performed when any tire is in an under inflated condition then the system will not report correctly.