Understanding Smart Sensors - Nomads.usp

190 Understanding Smart SensorsVNAWSNSMiniaturegyroscopesAccelerometersSNS computer(filter/integration)GPSPositioninformationVehiclecontrolcomputer(guidance/control)TransmitterunitWarningData busOther unitsActuatorsFigure 8.10 VNAW system.within a few inches or feet of a vehicle. Sonar has also been developed for theshorter range measurements. Sonar units are mounted at each corner of thevehicle. One sonar device operates at 50 kHz and drives a 300V transducer togenerate the sonic pulse.True road speed is one of the inputs that is required in the vehicle navigationportion of ITS. A microwave Doppler radar sensor mounted at the front ofthe vehicle can provide that measurement. Intrinsic errors due to the spread ofthe Doppler frequencies from the top to the bottom of the beam, sensor location,false signals from clutter, pitching, vibration, signal glint (irregularground reflections), short-term oscillator instability, and dirt are among theerror possibilities for this speed-sensing approach [23]. Microwave sensors arenot significantly affected by humidity, temperature, and air movement and donot require isolation of transmitter and receiver, which are considerations forultrasonic Doppler sensing.The complete ITS contains a number of other systems that ultimatelyaccomplish a number of goals, including safer travel on urban and rural roadsand higher usage of the existing highway system. Certain systems and subsystemscan and are being implemented separately. One element of ITS alreadyachieving high volume and usage in a variety of other applications is RF-IDtags.