Understanding Smart Sensors - Nomads.usp

4Getting Sensor Information Into the MCUSomeday we’ll find it—the rainbow connection.—Kermit the Frog from Jim Henson’s Muppets4.1 IntroductionThe sensor signal is only the first step toward a sensor that will ultimately providean input to a control system. Signal conditioning the output from the sensoris as important as choosing the proper sensing technology. Most transducerelements require amplification as well as offset and full-scale output calibrationand compensation for secondary parameters, such as temperature. Whether thesignal conditioning is performed as an integral part of the purchased sensor orperformed by the user, the accuracy of the measurement ultimately will bedetermined by the combination of the sensor’s characteristics and the additionalcircuitry. The signal conditioning circuitry that is required is a functionof the sensor itself and will vary considerably depending on whether the sensoris capacitive, piezoresistive, piezoelectric, et cetera.Once a high-level analog signal is available, it must be converted to a digitalformat for use in a digital control system. The A/D converter (ADC) can bean integral part of the digital controller, or it may be an intermediate standaloneunit. Different approaches are used for ADCs; the theoretical accuracy(resolution), indicated by the number of bits, is not always achieved in theapplication.This chapter addresses signal conditioning and A/D conversion for sensors.Examples are shown of available ICs that have been designed to simplify71