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DISCUSSIONsurge voltagewithstand voltage of theprotected instrumentmax. surge voltage VcVtDISCUSSIONtransmitteroutputsurge protectorfor RTDsurge protectorfor power supplysurge protectorfor RTDRTDtemp. sensorlightning surgelightning surge27QUESTIONA field transmitter was connected to a surge protector, but it was still damaged by a lightning strike. Can you tell me why?The surge protector that was selected could be incorrect for that specific application.12ANSWERANSWERThe maximum surge voltage of a surge protector to be used should be below the withstand voltage of the instrument(s) to be protected. This voltage level could be passed through the surge protector to the instru-ment(s) during a lightning surge. Be sure to confirm this specification before selecting the surge protector. Damage to protected equipment may occur because of this variable.QUESTIONAfter a lightning storm, there was no input from the remote RTD sensor to the temperature transmitter. There is no detectable damage to the transmitter. What could have happened?Is seems that the RTD temperature sensor was the only device damaged by the light-ning.13ANSWERANSWERIt is recommended that surge protectors be installed on both instrument and RTD to protect RTD sensor. If not, then the temper-ature transmitterʼs output signal could go upscale or downscale in this sensor is destroyed by a lightning surge. This means ex-cessive down time for the process that is being monitored and controlled.

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