Direct TPMS
The pressure information is commonly transmitted to the vehicle using radio frequency (RF) technology, though systems using mechanical, electrical or magnetic methods have been used over recent years.
[1] Other information can include a serial number, temperature, acceleration, direction of rotation and the status of the complete tire pressure monitoring system.
A typical direct TPMS (e.g. Ford,[4] BMW[5] or Toyota[6]) comprises the following components on a vehicle: Most direct TPMS systems use ultra high frequency (UHF) radio in one of the 'unlicensed' ISM bands (industrial, scientific and medical) for transmitting the data,[7] often around 433 MHz in Europe and 315 MHz in much of the rest of the world.
If the light is intermittent or if it stays on after correct inflation or replacement of a punctured tire then this indicates a fault with the direct TPMS system.
[4] This process requires the activation of the direct TPMS sensor using low frequency (LF) radio and the capture of the UHF data transmitted.
In automotive manufacturing plants, the activation is carried out using large antenna systems whilst in the dealerships and tire shops, hand tools are used.
As an alternative to this method, the vehicle can be programmed at the time of manufacture with the position of the tire together with its TPM serial number.
These typically use similar technology to 125 kHz RFID tags where the transmitted field is predominantly magnetic and can be easily detected by a small LF antenna located in the TPM.
The LF antenna is also often used by the TPM for configuration and to force transmission so that localization can be re-learned by the vehicle if a sensor is changed or the wheels are rotated.
In those systems, the TPM's have a method of detecting the rotational direction of the wheel, which forms part of the message transmitted to the receiver.
The TPM sensors currently fitted to high volume production cars worldwide are battery-powered, self-contained units which periodically measure tire pressure, and often temperature and acceleration.
The acceleration sensor allows the TPM to be placed in a low-power communication device mode, when the vehicle is stationary which can extend the battery life.
The transmitters are usually activated one at a time in sequence so that the vehicle can inform the driver of the location of the wheel with low pressure.
In addition, if the TPM detects a rapid change in pressure or too high a temperature, it will start to transmit more frequently so that the vehicle has more chance of receiving the information.
Aftermarket valve cap-based dTPMS systems, which require a smartphone and an app or portable display unit, are also available for bicycles,[15] automobiles, and trailers.
[16] The use of TPMS in vehicles in the USA was mandated in 2008 by the Transportation Recall Enhancement, Accountability and Documentation Act (or TREAD).
[17] The warning is displayed to the driver in line with 49 CFR Part 571 Federal Motor Vehicle Safety Standards (FMVSS).
