Tire Pressure Sensor
■Newer cars typically feature a tire pressure monitoring systems (TPMS) that will warn the driver when a tire is significantly under-inflated. This safety feature was deemed important enough that the United States Department of Transportation (DOT) and the National Highway Traffic Safety Administration (NHTSA) published a Federal Motor Vehicle Safety Standard. Tire pressure affects a vehicle's fuel economy, handling, and possible catastrophic tire failure. In this application note, over-inflated detection is also included. The system may also be used for anti-theft, warning when one of the sensors is not sending information (in that case, one of the tires may have been stolen).
■There are two TPMS system types. One of them is called Direct System. It is based on installing a pressure sensor in each wheel to directly measure the pressure in each tire, sending the information to the vehicle's on-board computer which warns drivers when the air pressure in any of their tires drops at least 25% below the recommended cold tire inflation pressure, or if the tire has 25% over the recommended inflation pressure.
■Direct systems are typically more accurate and reliable, and most are able to indicate which tire is under-inflated.
■The other system is called Indirect System. It uses the vehicle's anti-lock braking system's wheel speed sensors to compare the rotational speed of one tire versus the others. If a tire is low/high on pressure, it will roll at a different number of revolutions per kilometer than the other three and alert the vehicle's on-board computer. Indirect systems are unable to generate accurate readings in cases where all four tires are losing pressure at the same rate, such as the effects of time and temperature.
■In this implementation, the Direct Tire Pressure Measurement System will be used. In this case, the pressure will be measured and analyzed locally on each tire with the SLG46620V, sending the information of under-pressure, over- pressure or correct pressure to the central system (onboard computer or dedicated system) via the communication system (Figure 1). With this implementation, a TPMS may also be retrofitted on older cars by adding a small central system to the console of the car.
●Conclusion: In this application note, SLG46620V is used in a car safety system application as the ADC and preprocessing unit of a bigger system. We have shown how to condition the signal to meet the ADC and PGA specifications of the GreenPAK and the entire implementation is described. It is important to mention that the values used to compare the ADC conversion can be changed for different car and tire models, without changing the logic of the system.
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Application note & Design Guide |
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Please see the document for details |
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January 12, 2017 |
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AN-1168 |
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708 KB |
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