How long RS485 cable do I need ?

[suromenggolo]

I have some RS485 device, it will be connected to PC. look at picture
How long L maximum, from cross RS485 cable to device.?

Added after 6 minutes:

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[dika]

Re: How long cable RS485

the picture is not available?
range according to transfer rate is 35 Mbit/s up to 10 m and 100 kbit/s at 1200 m

 

[IanP]

Re: How long cable RS485

The L value depends on what is already used in the whole network (max 1200m of twisted pair) ..
If, for example, the cable length between a PC and all existing devices in the network (∑ of all nodes) is 800m, your L should be <400m ..

Regards,
IanP

 

[suromenggolo]

Re: How long cable RS485

Oke...
Is this like, if i connected bulb lamp to main line house electrical..?

 

[IanP]

Re: How long cable RS485

Well, I wouldn't make such a comparison ..

In power lines when you add more load(s) on long cables the voltage will drop because of the resistance of the copper wire, in data transmission over twisted pairs the limit will be reached mostly because of the capacitance of the twisted cable (for CAT5 cable it is ≈15pF/ft) ..

Regrads,
IanP

 

[rosarioantony]

Re: How long cable RS485

Rs485 standard say 4000ft from end to end.terminal devices need to be terminated by terminating resistors usually 120 or 180ohms .