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RS232/serial cable length

Discussion in 'Networking' started by vette, Jan 26, 2004.

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  1. vette

    vette Thread Starter

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    What is the maximum length that you can run a serial cable before having communication problems?
     
  2. Bob Cerelli

    Bob Cerelli

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    A lot depends on the speed you want to transfer data. At slower speed like 9600, you can easily go 50 feet. Special cables may extend that even further.
     
  3. JohnWill

    JohnWill Retired Moderator

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    The maximum run length is going to depend more on the devices on the other end than the length of the cable. You can use low capacitance cable and run 9600 baud 100's of feet, I've done it countless times. However, since RS-232 is single-ended, common mode voltages become an issue if your building grounds are not good. I've had fireworks from serial devices when grounds in 100 year old buildings in Wall St. trading firms locations had what looked like 100 year old wiring! :D If you have a long run, the best bet is a current loop and optical isolation, much easier to get going reliably. :)
     
  4. vette

    vette Thread Starter

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    I need to run a cable from my pc to a cnc router which would be 50 to 60 feet or more, does that sound like a reasonable length or do I need to set my connection up differently?
     
  5. JohnWill

    JohnWill Retired Moderator

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    Other than grounding considerations, I don't see any issue with 9600 baud at that distance. RS-232 isn't my first choice nowadays for any length of cable, I prefer an isolated connection, but it should work.
     
  6. vette

    vette Thread Starter

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    What exactly do mean by an isolated connection?
     
  7. JohnWill

    JohnWill Retired Moderator

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  8. vette

    vette Thread Starter

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    Makes sense, thanks for the info.
     
  9. logers

    logers

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    I'm interested in optical isolation, I have lab equipment in a separate part of the building as the server room, and I'd like to keep servers out of the lab.

    Since the lab equipment software is fairly finicky I'm pretty sure that I need to keep the serial-to-serial connection. My question is, can I do a serial-optical-serial connection that is as reliable as serial connection with the distance/protection benefits of optical isolation?

    What equipment is anyone using to do this?
     
  10. JohnWill

    JohnWill Retired Moderator

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    Sure, there is no reason the optical isolation won't do the job. There are also serial <> Ethernet products that may solve your problem, you'd have to look at the specific applcation.

    You need to first determine how many control lines are used in the serial cable, then pick the product to match the requirements. For long runs, especially if you already have a network cable to the location, the Ethernet solutions might be attractive. Lava Ethernet Link is one such product that may be an option for you to consider.
     
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