RS485????±??¤·???
The Analysis of Protecting RS485 System
?ú????×??????????¤???????????????¨NDSC?? ?? ±? ??±???

?? ????±?????RS485?????·±??¤????·?????·?????·??ú?????????????ò???é?????¤·???????????·?·¨???????÷??·?·¨?????í???????è????·?????????·?·¨?????±?????°??????????????×??ó????????PCB???????????á?????¨?é??

???ü????RS485????????????±??¤??·??÷±??¤


?? ??

RS485????EIA??1983?ê?á??????????????????·???±ê×????ú×???±ê×?????·??÷????????·???????·??????¤×÷·?????????????RS485?¨TIA/EIA-485???¨??±???×÷??TIA/EIA-422±ê×??????????????????§???à?????¨32?????????????????????à?÷???????á?§???ü?à???????????à???¨×??ó4000???????????????é?????¨200mV???????????¨???????±?????è????????????×÷?????????ò????±????????è±??ò???????à???????à???¨???·????????????·???????

????????????485???????????????à?ò?????°?ì????×è?????????ò????????????????????????×è????????±??????????·±??¤·??????á??RS485????????????????·?????


???ò·???

?????????????°???·??????·??????????????¨??RS485????±?????????·??¤??????RS485??????????°???????????????×??????á???????§???·???ò???????????ó????±??????á??????×?????????????????????RS485???·???à???÷??????????

?í????RS485??·??÷??A??B?????????á??????????????????????????±?????????±??????á???????ó??"??"??±?????·???????????????????·??§??-7V??+12V????????·??§????±????????????÷????RS485?????÷?¨???ì??A??B????????×??????????¨??????TTL???????????±A?¨-????B?¨+??????????Vab?¨A-B???ó??+200mV?±??????????????"1"????????????-200mV?±??????????????"0"?????????????????????????±???????????????????????????????????????????ò???±????????·??ú?±??????×???×÷????????·??????quot;??"??×?????×è???????????????§?????????????????????????????§??????????????????????·??ú?±????????·??ú?±???ù???????????????????ú?ú??°????§·ü?????????????±?????????????????????????????????????????????????ù???????????????????????????????????????ó??????????

??????±??¨?????×?????????????????????????????????±??°é?????ó????????????????????????????/???÷??????±?ANSI??IEC?ù?¨?????????????¨?×?÷?????¨??????ITU K20/K21±ê×????????à????×??????????÷????????????????????×??????????ù?¤???????ù?????????????????????????????±?ò?????á?????????¨×????????????????????????????è???ì?????ó??????

??????RS485????????±??é???????÷??±??¤???????×???????·±??????????ù???÷??????????????"??"???????????????÷?¨???÷?????????????·???¨????????·????????????í?????????§?????????????????????÷?÷???????????????????í???????????÷???ù????"??"????????×è???????????????ó?????????ù??????????????????????±??¤??·?·¨??????±??¤??·??÷±??¤??


±??¤·?·¨

????±??¤

??·?????°????????????÷?÷?????·?????????????????????????????¨????????????????RS485???????¨?????????????÷??±????÷?????÷?÷????????I/O???·?????????÷??????????????????????????×??????????????????????????????·?????????????????????÷?????¨?÷???????¨?¨????1000-2500V?????????????á?????????à±??¤?????ü???ò??·??÷(shunt)???????????ò??????±?×??????????±?????????????????????????????????????á?????????÷????????×????????????à±??¤????????????±??????§??????????????????????????±???????????????

????·????????????????ó???????????????????????????????è??????????????????????????????????????????±????????????·????????1?ù????

??1 ????±??¤?¨????

·??÷±??¤

·??÷±??¤?????????????????÷?????????????????°????±??¤?÷????TVS??????????·???·??ú×÷????????????·??????à?÷???????é?????¤×÷???ù?è?¨???????????????????·???????????????????÷??????????????????×è?????¨?·?????????¨×??????±???????÷??????????±??????÷????·???????????????×???????????????????

·??÷±??¤?????¨?????????????????à??±??¤??????±??¤?¨???????????????÷??????TVS????????????·?·¨×??ó???????????????ò??????±????????????????????à??±??¤????????2??????????±??¤???÷???¨??????????·??????????????????????ü???????????????????????????????????ó???÷?????????????????ì???±???????ì????????????????????×è?ò???????ú??????×è?????¨?¨????10 ????????PTC??????????·??????????÷???§?????í??·????????????????????????¨???????????????ì?????????ì??TVS??????????×÷?????ü??????????·??????ó???÷?±???????·?????????????????ó????????·???????????????????°???·??§??????????±??¤???????·?????à±??¤?????????????ó????????·??????????????????¤??????1?×?????è?????????ò??±à?????????????????????????ü????±??¤?§????

??2 ?à??±??¤???·?¨????

???????·??????????????????×÷±???????3?????????·???????????????????ü????????????±??¤????·????????à?·??????????????????????ר??????RS485???·±??¤???÷??????TED-485??

????±??¤?÷???è???ü???ó???????????????????¤?±??????±???±??¤?÷?¨?????????ü±?±??¤?????????????¤×÷?????????????????ü???·???????¨????????????RS485???????????¨???????¨????6-8V???÷???????????à·??¤?÷??????????????????????????

×é??±??¤

?í??????????????????·?·¨×é??????????4??·???1????????????±??¤?????·?????????????????????????°?ì????·??÷±??¤?÷??????×è?????????????????????÷???÷?????????????????í??????????????????????·???2??????·¨???????§???ó?????????é??????·??÷?÷?????????÷????±??¤??????????????????????????????????????·??÷?÷????×÷????????A??B????????????????×??????????????????????±?????¤?????????????????????????á??????????±??¤??

????·????????????á????°??????????±±??¤?????????í?÷???é??????????????/???÷??±????????????????????????è??????????????"??"???????????????????¨????????


PCB?è??????

??????485±??¤???·???????????????ó?????????????????????±?????????????????????????????÷?????????±????±??¤???·??485??????°??????????í??×?????2mm????????????????±??¤?±??????????±?????????????????????"??"????????????EMI??????


?á????

???·±??¤??????RS485???????í?¨?????????????????á??????????????????????????????????×???????????RS485??????????????????????±??¤???·????·???×÷???????ü???????????ò?????????§????×?????????·??÷±??¤???¨???à??±??¤???????×??????·?°???????±????ù??????????·???????