Agilent Measurement Journal - Issue 3 - 2007 - (Page 39)

P Passenger safety is a major focus of all automotive designs, supported by ongoing efforts to continually enhance safetyrelated features. One such feature is the tire-pressure monitoring system (TPMS), which provides either real-time pressure readings or under-pressure warning indicators to the driver within the comfort of the vehicle cabin. Studies have shown it is common to ﬁnd vehicles traveling with under-inﬂated tires. This condition has unwanted side effects: additional stress on the steering system, accelerated tire wear and decreased fuel economy. Unfortunately, it also has some very sobering consequences: Statistics show that more than 400 fatal and up to 10,000 non-fatal accidents per year are caused by ﬂat tires or blowouts. Twenty percent of ﬂat tires and blowouts are the result of under-inﬂated tires. Statistics such as these are one reason the United States enacted legislation requiring all new passenger cars and small trucks with gross vehicle weight (GVW) of less than 10,000 pounds be equipped with TPMS. The main purpose is to ensure better handling and greater safety by giving drivers real-time warnings about lost tire pressure. The gradual phase-in of the new requirements began in October 2005 (20 percent of new vehicles) and culminated on September 1, 2007, when all light vehicles sold in the United States must equipped with some type of TPMS. Comparing two approaches The owner’s manual of any recent vehicle includes the recommended tire pressure for the factory-installed tires. The United States legislation sets a threshold of no less than 25 percent deﬂation from the recommended pressure. Any reading lower than the threshold triggers the TPMS, which will then warn the driver. Two types of monitoring systems are currently in use: indirect and direct. Indirect systems leverage signals measured by typical antilock braking systems (ABS) that use wheel-speed sensors to regulate ABS operations. Data from those same wheel-speed sensors can be used to compare the rotational speed of each tire; an underinﬂated tire has a smaller circumference and therefore rolls faster than the other tires. Unfortunately, this method requires a bit of time and distance before the problem becomes apparent. Also, it might not be detected if all four tires have deﬂated by the same amount and are rotating at the same speed. In comparison, direct monitoring has proven to be a more accurate and reliable measure of tire pressure. This method uses one base receiver unit that monitors four transmitting pressure sensors — one afﬁxed to each tire. The receiver unit is commonly placed inside the vehicle and drives an indicator on either the dashboard or a separate display. One sensor is mounted inside each tire where it measures pressure and transmits the reading over radio frequency (RF) to the base module. Each transmitter is normally encoded with a unique serial number or code, allowing the base receiver to identify each tire separately. Agilent Measurement Journal 39

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 3 - 2007

Applying Ingenuity to the Measurement of Emerging Technologies Contents Emerging Innovations Department Delivering Bigger Benefits by Optimizing Customer Workflows Measuring Material Properties at the Nanoscale Utilizing In Situ Atomic Force Microscopy in Life Science, Pharmaceutical and other Bio-Related Applications WiMAX™: Plotting a New Path to Global Mobility Addressing the Triple Complexity of Triple-Play Networks What Next for Mobile Telephony? Exploring the Inner Workings of Tire-Pressure Monitoring Systems Developing, Assessing and Applying a High-Resolution Thin-Film Magnetic Probe Making Accurate Settling-Time Measurements Using a Vector Network Analyzer Applying Metabolomics Methods to the Study of Bacterial Leaf Blight in Rice Plants Measuring Stream Dynamics with Fiber Optics survey

Agilent Measurement Journal - Issue 3 - 2007

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