Understanding Smart Sensors - Nomads.usp

268 Understanding Smart SensorsSemiconductor sensor designs and applications have a system requirementthat is normally not a problem in presemiconductor mechanical sensors,namely, ESD. Automotive and other applications generate high levels of ESDduring manufacturing or in service. As a result, automotive manufacturers specifysome of the most stringent ESD testing to qualify components. Automotivemodule manufacturers are indicating that future specifications will require anyIC pin accessible outside the module to withstand 10-kV ESD with 250 pFand 1,500Ω load. That means peak currents approaching 7A and energy levelsin the range of 12.5–14 mJ must be tolerated. The output connections of sensors,power, and control circuitry can be exposed to ESD during assembly oroperation [2].Sensors must be designed to meet levels of EMI commonly found in theapplication or required by industry specifications. EMI is a disturbance or malfunctionof equipment or systems caused by the operation of other equipmentor systems or by the forces of nature. Distributed control systems can be susceptibleto high-frequency switching, which is common in computers, switchingpower supplies, and power control. Figure 11.8 shows an industrial processControlleddevice orprocessFloat (isolate)Commercialand dieselgeneratorUPSSensorControlrelaysTransferswitchCrosstalk incable trayTransientsConductedEMIRadiationpickupHost computeror other PLCsLANtokenringProcesscontrolleror PLCCable spreadingroom or closetDatahighwayMonitors, display,and status indicatorsFigure 11.8 EMI in process control system. (After: [19].)