- Door WF-sensoren
A direct tyre pressure monitoring system measures the pressure inside each tyre with sensors mounted on the wheel and transmits that data wirelessly to an in-cabin receiver. Compared with indirect systems, it can show the instantaneous absolute pressure for every tyre. Sensitivity and resolution determine whether the system will alert early enough. This article focuses on how piezoresistive pressure sensors are implemented in TPMS, and highlights three core concerns: sensor resolution, temperature drift control and power consumption management.
Catalogus
1. Introduction to Direct Tyre Pressure Monitoring Systems
A direct system places sensors inside each wheel which directly measure tyre pressure, then wirelessly sends those measurements to a receiver in the cabin. Its strength is providing the immediate absolute pressure for each tyre, with high detection accuracy so it can warn of small leaks or pressure drops. By contrast, indirect systems rely on the vehicle’s ABS wheel-speed sensors to spot rotational-speed differences between tyres; this approach cannot report actual instantaneous pressure values, and it fails to alarm if tyres on the same axle or the entire vehicle lose pressure simultaneously. Direct systems typically fall into two groups: battery-powered active modules and passive modules (often using surface acoustic wave, SAW, technology) that don’t require a battery. Active modules are mature and flexible in signal processing but are constrained by battery life; passive designs save power but require standards and integration at the tyre-manufacturer level to be practical.
System types and comparison
Active systems pair piezoresistive or capacitive MEMS pressure sensors with a low-power radio module, providing high sampling rates and direct measurement. Passive systems typically use SAW sensors that alter surface acoustic waves in response to pressure; they need an RF interrogator and do not require onboard power. When choosing between them you must weigh real-time performance, service life and implementability.
2. How Piezoresistive Pressure Sensors Work in TPMS
Piezoresistive sensors are made using silicon MEMS processes that place resistive elements on a diaphragm. Applied pressure deforms the diaphragm and changes those resistances; that change is converted to a voltage with a Wheatstone bridge or differential amplifier. This approach is straightforward, the linear range can be corrected in the signal chain, and silicon processing gives good batch consistency. For tyre use you typically see ranges like 0–7 bar (or lower for passenger cars). Design goals centre on high resolution (to detect small pressure changes), low temperature drift and strong shock/vibration resilience.
From diaphragm strain to resistance change
Diaphragm thickness, the layout of strain gauges and their placement control sensitivity and full-scale output. Engineering choices must balance geometry and process parameters to hit the required resolution while keeping stability across the temperature band. For tyre monitoring, a resolution better than about 0.05 bar is commonly needed to detect small leaks reliably.
3. Sensor design and packaging essentials
The wheel environment exposes sensors to heavy vibration, wide temperatures and moisture — so packaging is critical. The WF162F-style device shown in the image has a top pressure port and multiple solder pads on an SMD footprint; a metal cap coupled to an SMD substrate can provide mechanical strength while offering a pressure inlet. Packaging materials must resist salt spray and repeated shocks; the pressure port should be designed to avoid clogging by dust or debris and match the rim’s mounting hole. Electrically, pads must withstand fatigue and provide robust ground and power return paths.
Pressure port and packaging material choices
The pressure port needs to transmit internal pressure accurately while resisting particulate blockages; a metal cap with a polymer base often gives the right mix of sealing and mechanical toughness. Material selection should account for coefficients of thermal expansion and working temperature range to avoid mismatches that cause drift at extreme temperatures.
4. Signal conditioning and wireless transmission
The raw voltage from a piezoresistive sensor must be amplified, filtered, converted to digital and temperature-compensated before a microcontroller and low-power RF block transmit it. Key steps include matching a low-noise amplifier to a high-resolution ADC and applying real-time temperature correction. Wireless links often use Bluetooth Low Energy or proprietary RF, and antenna layout plus transmit power settings need to balance link reliability against battery life.
A/D, temperature compensation and power management
High accuracy benefits from a high-resolution ADC (often 24-bit or similarly precise) combined with digital filtering to reduce noise. Temperature compensation can be a simple first-order correction or a lookup-table approach to trim drift across operating temperatures. For active modules, power management techniques like sleep cycles, event-driven sampling and low-power wake modes are essential to extend battery life while preserving measurement reliability.
5. Performance metrics, test methods and reliability validation
Key TPMS sensor metrics include absolute accuracy, resolution, linearity, temperature coefficient (mbar/°C or ppm/°C), long-term drift and vibration tolerance. Validation requires testing in temperature chambers, vibration rigs and humidity cabinets and performing multi-point calibration against a pressure standard. System-level testing should also measure wireless packet loss, receiver sensitivity and false-alarm rates.
Standard tests and environmental stress
A standard test regimen includes multi-point pressure calibration at several temperatures, thermal shock cycles, mechanical vibration and damp-heat tests. Long-term reliability trials (for example, 1,000-hour accelerated ageing) reveal how packaging and materials degrade under road conditions and guide improvements to design and warranty strategy.
Conclusie
When using piezoresistive pressure sensors in direct TPMS, engineering priorities are clear: ensure high resolution with minimal temperature drift, provide robust packaging and optimise wireless power consumption. WF162F-style devices in the picture show a common approach — metal-capped SMD packaging with a top port that meets the mechanical needs of wheel mounting. Ultimately, a production-ready system balances cost, lifetime and measurement accuracy, and only rigorous environmental testing and production calibration can ensure consistent product quality. Teams that invest early in packaging materials, temperature-compensation algorithms and power-management strategies will reduce long-term maintenance and recall risks.
De bovenstaande introductie schetst slechts het oppervlak van de toepassingen van druksensortechnologie. We zullen doorgaan met het verkennen van de verschillende soorten sensorelementen die in verschillende producten worden gebruikt, hoe ze werken en hun voor- en nadelen. Als u meer informatie wilt over wat hier wordt besproken, kunt u de gerelateerde inhoud verderop in deze handleiding bekijken. Als u weinig tijd heeft, kunt u ook hier klikken om de details van deze handleidingen te downloaden Luchtdruksensorproduct PDF -gegevens.
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