Direct tpms methods use pressure sensors to measure pressure in each of the four tires. Then these sensors transmit the pressure data via a wireless rf transmitter to a central receiver. The receiver communicates to a display that informs the driver which tire is underinflated. The tag in each wheel is designed to send a warning signal when a tire's pressure drops below its specified safety level. Tire-mounted pressure sensor is shown in figure 1. Under-inflation has been cited as a cause of tire failures such as tread separation or tire blowouts. It is also responsible for shortening tire life and reducing fuel economy.
Technical specifications for display:
Operating frequency: 433.92mhz 8khz
Operating current: 4ma
Static current: 100
Operating voltage: 2.6-3.6v
Operating temperature: -20-+85
Built-in battery capacity: 3.2v/160ma
Charging temperature: 10-+65
Solar charging current: 15ma (at 5500lx 25/77)
Usb charging current: 40ma