| ??? 10/19/08 11:28 Read: times |
#159196 - Does that mean, ... Responding to: ???'s previous message |
K. said:
There is no isolation between the product and external RS485 device, but only DATA+ and DATA- lines are used. ...that signal ground isn't connected from the "product" to the "external RS485 device"? This is a big mistake, because due to your earth potential shifts huge common mode interferences can hit the both ends of RS485 cable! Route signal ground in parallel to your Data+ and Data- lines. Also, try to use RS485 transmitters that can withstand big common mode voltages, like the LT1785, for instance. K. said:
The earthing on the 230V supply point is not good and some times a voltage of 90+V is found between Neutral and Earth. Yes, which results in colossal and destroying common mode interferences... By the way, it's a good idea to handle signal ground, cable shield and protective earth like the PROFIBUS people: http://www.8052.com/forum/read.phtml?id=127782 Kai |
| Topic | Author | Date |
| MAX232 failure | 01/01/70 00:00 | |
| MAX232 failure | 01/01/70 00:00 | |
| Does that mean, ... | 01/01/70 00:00 | |
| Yes, ground is not connected | 01/01/70 00:00 | |
| exactly what is connected to the MAX232... | 01/01/70 00:00 | |
| But it truly should... | 01/01/70 00:00 | |
| Thanks for your suggestion | 01/01/70 00:00 | |
485/232 with 'unreliable' ground | 01/01/70 00:00 | |
| It is a handheld terminal | 01/01/70 00:00 |