Freescale has revealed that it provides the world's smallest MEMS tire pressure monitor for consumer vehicles, but is now raising its claims by offering the world's highest pressure sensor for heavy trucks, buses and construction vehicles. Many tire pressure monitors use bulk machining of silicon blocks to realise tire pressure MEMS monitors, but the company uses standard low-cost surface machining to realise a tire pressure monitor that uses capacitance to be much more accurate than the bulk-machined or even other surface machines tire pressure sensors.

Freescale's system-in-package (SiP) contains a two-axis accelerometer, an S08 8bit processor with 512 bytes of RAM, 16KB of flash (8k for Freescale library, 8k for applications), dedicated state machines for reduced power consumption, six general-purpose input/output (GPIO) ports, including two analogue-to-digital (A/D) inputs, a low-frequency (125kHz) receiver for programming user-defined functions and making periodic resets, and a high-frequency (315MHz to 434MHz) RF transmitter supporting rolling encryption to issue warnings to the fleet manager and to read out a "prognosis" of each tire's condition.

The built-in accelerometer turns off the device when the vehicle is sitting still, but can also record the acceleration while in motion and also includes a temperature sensor to include in the correlations. By optimising those parameters with advanced data analytics for optimising predictive maintenance and tracking driving behaviour, the tires not only last longer, but a significant increase in vehicle fuel efficiency can be realised, less down time per vehicle and optimal vehicle usage, according to Freescale.

"We are entering the era of the smart tire, one that can tell you when and how it needs to be rotated, when it needs to be replaced and other prognostic diagnostics, instead of just telling you how much pressure it holds and when it needs to be aired up," stated Ian Chen, head of Freescale's software and algorithms for sensor solutions.

Measuring just 7mm x 7mm x 2.3mm and weighing just 0.3g, the tiny sensor can be built right into a tire by its manufacturer or can be added-on at the valve using an after-market device from Advantage Pressure Pro and others. The FXTH87xx can measure pressures up to almost 217.5 pounds per square inch (1500 kilopascal second, kPs).

"Fleet managers who have been beta-testing the new FXTH87xx tell us that they could save up to a million dollars a year by keeping close track on the wear and tear on those huge tires on their 18-wheelers, knowing when a where to rotate them and keeping the at the optimal air pressure for the loads they are carrying," Chen noted.

Accuracy is ±2.4 pounds-per-square-inch (psi or in metrics plus-or-minus 17kPa) operating the range of 14.5psi (100kPa) to 217.5psi (1500kPa).

By: DocMemory
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