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Tire pressure monitoring systems are designed to keep track of the amount of air in the tires of a vehicle. These systems typically provide real-time information about tire pressure by means of sensors and warning indicators. There are two different types of tire pressure monitoring systems. Direct systems utilize radio equipped air pressure sensors mounted to each individual tire that send warning signals to a dashboard receiver. Indirect systems make use of a vehicle’s anti-lock braking system to warn the driver of low tire pressure.
Direct tire pressure monitoring systems provide a very accurate means of keeping track of vehicle tire pressure. This type of system utilizes a radio transmitter equipped sensor located on each wheel of the vehicle. Each sensor monitors the air pressure inside of the tire and sends a radio signal to a dashboard receiver when an unacceptable condition is present. The sensor may be installed inside the air chamber of the tire or inside a specially designed valve stem located in the wheel itself. The individual sensors used in a direct system make it possible to monitor the air pressure in multiple tires at the same time.
Direct systems are generally the most comprehensive means of tire pressure monitoring, but they do have certain drawbacks. The sensors employed in direct tire pressure monitoring systems rely entirely on batteries. Although these batteries have a typical lifespan of 7-10 years, they can fail much sooner in extreme temperatures. Batteries will also likely need to be professionally replaced at least once during the average life of a vehicle. Sensors mounted in the wheel’s valve stem can sometimes be damaged during tire repair or replacement and will have to be replaced to keep the system functioning properly.
Indirect tire pressure monitoring systems are usually incorporated into the anti-lock braking system. The system’s wheel-speed sensors are utilized to evaluate the rotational speed of each wheel with that of the others. A tire with low air pressure will usually roll at a different rate of rotation than at normal pressure. This change in rotational speed alerts the anti-lock braking sensor, and a warning is then sent to the dashboard display. Indirect systems are often an inexpensive way to incorporate tire pressure monitoring into new vehicle designs and meet governmental safety requirements.
Along with being less expensive to install, indirect tire pressure monitoring systems are also less comprehensive. Unlike direct monitoring, indirect systems cannot tell the driver exactly which tire is low on air. This system also has no method of indicating if more than one tire has low air pressure. False alarms are sometimes generated when a tire spins on a wet or icy roadway. This type of system must also be manually reset by the driver and could accidentally be reset when tire pressures are low or uneven.