Humidity sensor offers clear view

Improved automotive safety has many aspects but starts with the driver having a clear view of the entire road. To avoid vision-restricting condensation, many carmakers offer automatic defogging systems based on input from humidity sensors. A humidity sensor from Sensata Technologies, formerly the Sensors & Controls division of Texas Instruments, promises improved performance for these systems. The response time of the company's thin-film polymer capacitive sensor is five times faster with twice the initial accuracy of traditional resistive sensor technologies.

The capacitive sensing element has a porous electrode that allows water vapor to pass through to the thin-film dielectric as air is drawn over the element. An Application-Specific IC (ASIC) processes the capacitance value and measurements from a separate temperature sensor to create an accurate relative humidity reading. In contrast, resistive sensing techniques measure the voltage change between two resistive materials as water vapor collects on the surface of the sensing element. The larger resistive elements typically require more water vapor to accumulate and consequently have a slower response time. Over an operating range of 5 to 95 percent relative humidity, the thin-film capacitive sensor has a response time of less than 10 seconds.

Compared to the plus or minus 10 percent initial accuracy of competitive sensors that use capacitive or resistive technology, the thin-film sensor has an accuracy of plus or minus 4 percent. After exposure to typical automotive environmental stress testing and over the useful life of the vehicle, the accuracy may shift plus or minus 4 percent, compared to an industry average plus or minus 10 percent drift during the vehicle's lifetime.

An additional benefit of the sensor-controlled defogging system is reduced energy consumption for improved gas mileage. A recent J. D. Power and Assoc.'s survey estimates that it takes four times more energy for defogging a windshield than preventing fogging from occurring with a continuously running system.

CONTACT: Abelardo Gonzalez, Sensata Technologies, Tel.: 508-236-3800; e-mail: [email protected]

Get more information on Sensata Technologies' automotive humidity/temperature sensors.