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The Expanding Role of Today's Sensors
Automotive, industrial and consumer products employ more
Randy Frank, Contributing Editor -- Design News, October 6, 2008
In control systems, sensors provide the information for measuring, monitoring and controlling. In some consumer products, sensing provides additional functionality. For example, sensing the status of a mobile device without using a mechanical switch can transition the product from a power-conserving sleep mode to the ready-to-work mode with the keypad illuminated and other circuitry powered for operation. Several sensing technologies provide the sensing capability.
One solution proposed by OSRAM Opto Semiconductors uses the company's SFH7740 and SFH7741 optical proximity switches. Distance measurements detect the operating status of the mobile devices and are used to switch the display and keypad off when they are no longer needed, and also adjust the volume of the loudspeakers.
Another approach from ROHM Electronics uses Hall Effect ICs in different configurations to detect the open/closed change in flip phones, as well as sliding or screen pivot status of cell phones and other portable devices. The low average current (as low as 3.5 µA) of ROHM's Hall Effect ICs is important to minimizing the total current draw in the portable product.
Accelerometers are also used for power conservation. Tire pressure monitoring systems, such as Freescale Semiconductor's MPXY8300, add four or even five new pressure and other sensors, such as acceleration and temperature, to today's vehicles. The sensors are designed to meet Federal Motor Vehicle Safety Standard (FMVSS) 138 and car manufacturers' requirements for other regions, as well. While accurately detecting the drop in pressure of one or more tires requires pressure and temperature measurements, ensuring long battery life uses an accelerometer at each wheel to detect motion and turn off the system when the vehicle is stopped.
Once proven in one application, many sensors find new applications in other markets. Infineon's KP124 and KP125 have an accuracy of ±1.2 kPa (±1.5 percent full scale) over an operating range of 40 to 115 kPa at temperatures from -40 to 125C. These automotive products have recently been extended to handle process control, gas flow, consumer and other industrial pressure measurement applications.
This section includes specific trends and products in the areas of triaxial accelerometers, linear position sensors and pressure sensors. Many of these provide additional functions, as well.
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