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> Rs485 - Help
partha
Posted: February 10, 2009 02:40 pm
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Hello all,
We manufacture instruments using Rs485 connectivity. We have connected about 30 units on a 4 wire RS485 network (multi drop configuration). The instrument that s addressed by the host (PC) only enables its transmission and sends a packet to PC. Over some time we notice the RS485 ICs becoming very hot and eventually burning off and the PCB in the area is also showing burnt marks. We are not able to fine the reason for this behavior. Can some one indicate where the proble could be? Thank you

Partha
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CWB
Posted: February 10, 2009 02:59 pm
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supply voltage is too high ?
do you have "on board" regulation per unit ?


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partha
Posted: February 10, 2009 07:32 pm
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Nope the voltage is within range - 5V

Partha
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SiliconBurner
Posted: February 10, 2009 10:12 pm
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Show the schematic.


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Colt45
Posted: February 11, 2009 06:55 am
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groundloop hell?

all the RS-485 transcievers I've seen can't take more than 5V common mode, if your grounds are out by more than that you'll need some opto-isolated modules.


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partha
Posted: February 12, 2009 04:05 am
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Hello Colt45,
Yes the cable lengths are reasonably high. But what is this ground loops you have mentioned? We have a common ground line connecting all the devices. How can one use op-to couplers in such a case? Can post some suggestions? In our case each unit is given a unique ID and all the units are in listen mode with their transmitters in off condition. When the host addresses a particular unit only that unit will enable its transmission and send a reply. I await your reply. Thank you.

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