Grossel
Well-Known Member
In a facility , there are about 5m (15 ft) between a modbus master and slave1 (there is only those two devices to be connected to each other this time).
Since this facility is kind of - takes time to go there - I want to make the best possible RS485 bus.
There are expected to be some low frequency noise in the nearby area, and the baud rate will be set to 9600bps (but I want it to support higher in case of more equipment get added to the rs485 bus later on).
The issue is that the modbus master are manufactured with one RJ45 socket for RS485 instead of simple screw terminal. This makes it difficult to make a proper cable (adding a resistor very close to the RJ45 plug just create a weak spot and somewhere a jacket or strap may get caught). This is not wanted as a solution.
The alternatives:
Since this facility is kind of - takes time to go there - I want to make the best possible RS485 bus.
There are expected to be some low frequency noise in the nearby area, and the baud rate will be set to 9600bps (but I want it to support higher in case of more equipment get added to the rs485 bus later on).
The issue is that the modbus master are manufactured with one RJ45 socket for RS485 instead of simple screw terminal. This makes it difficult to make a proper cable (adding a resistor very close to the RJ45 plug just create a weak spot and somewhere a jacket or strap may get caught). This is not wanted as a solution.
The alternatives:
- Assumed best for signal. But will cause a clump and weak spot on the wire that is not wanted.
- Tap wire for modbus master. Assuming almost as good. However I cannot find (or phrase the right question for AI to understand) any source online that specify the lowest ratio between length of tap wire (closest to end) and the last wire segment to where the end resistor are connected. I.e. Can the ratio be as low as 1:1 or should the wire segment closest to the end be longer than some given distance ?
- Insert a separate screw terminal bus bar for connecting the resistor. This is the method I would want to use (because least amount ow work). But then then there will be a wire segment after the terminal resistor, about 40cm (1 1/3 ft) in order to reach around the master device.