Understanding Smart Sensors - Nomads.usp

2 Understanding Smart Sensorsobserver. The transducer converted the physical quantity being measured to adisplacement. The observer initiated system corrections to change the readingcloser to a desired value. The typical blocks of a measurement system are shownin Figure 1.1 [1].Many home thermostats, tire pressure gauges, and factory flow metersstill operate in the same manner. However, the advent of microprocessor technologyinitiated the requirement for sensors to have an electrical output thatcould be more readily interfaced to provide unattended measurement andcontrol. That also required the analog signal level to be amplified and convertedto digital format prior to being supplied to the process controller.Today’s MCUs and analog-to-digital (A/D) converters typically have a 5Vpower supply, which has dictated the supply voltage for many amplifiedand signal conditioned sensors. However, the reduction in the supply voltagefrom 5V to 3.3V and even lower voltages and the presence of more than onevoltage in a system pose challenges not typically associated with even the smartestsensors. Separate integrated circuits (ICs) are available to handle the varietyof voltages and resolve the problem, but they add to system and sensorcomplexity.Commonly used definitions for the terms sensor and transducer must bethe first in the list of many terms that will be defined. A transducer is a devicethat converts energy from one domain into another, calibrated to minimize theerrors in the conversion process [2]. A sensor is a device that provides a usefuloutput to a specified measurand. The sensor is a basic element of a transducer,but it also may refer to a detection of voltage or current in the electrical regimethat does not require conversion. Throughout this book, the terms are usedsynonymously, because energy conversion is part of every device that is discussed.The mechanical measurements that require a transducer to provide anelectrical output are listed in Table 1.1.CalibrationinputAuxiliarypower (not alwaysrequired)Auxiliarypower (usuallyrequired)IndicatorMeasurandSensor/transducerSignalconditionerRecorderProcessorControllerFigure 1.1 General sensing system.