Modbus RTU "start topology"

rQx

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Join Date
Oct 2010
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Trelleborg
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Hi,
Would this topology work as Modbus RTU? I wan't to wire all slaves to my cabinet, connect them to terminals and then place jumpers to connect them. Instead of have them from slave to slave.

Namnlös.png
 
Yes, this should work. Please review the specifications for RS485 communication on your equipment to ensure you are within them.
Distance - distances up to 1,200 m (4,000 ft)
The value of each termination resistor (If not built into the equipment) should be equal to the cable characteristic impedance (typically, 120 ohms for twisted pairs)

Regards,
 
gclshortt said:
Yes, this should work. Please review the specifications for RS485 communication on your equipment to ensure you are within them.
Distance - distances up to 1,200 m (4,000 ft)
The value of each termination resistor (If not built into the equipment) should be equal to the cable characteristic impedance (typically, 120 ohms for twisted pairs)

Regards,
Click to expand...


And 120ohm resistors only to bus ends (master and slave3 on this)
 
Thanks! Folowup question, isinde a cabinet between VFDs. Is it recommended to use shielded cable also here? Since it's a VFD it will produce noise that will interfere with the modbus communication?

And if it's equipment with no noise, can I use just normal wiring that I twist?

Or what is the standard way?
 
rQx said:
Thanks! Folowup question, isinde a cabinet between VFDs. Is it recommended to use shielded cable also here? Since it's a VFD it will produce noise that will interfere with the modbus communication?

And if it's equipment with no noise, can I use just normal wiring that I twist?

Or what is the standard way?
Click to expand...

Use cable with a shield everywhere. Use cable designed for RS-485.

https://www.belden.com/products/industrial/cable/bus-cable/rs485
 

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