Results 1 to 5 of 5

Thread: RS232 Cable Shielding Opinions

  1. #1
    Join Date
    Sep 2005
    Location
    Wisconsin
    Posts
    996
    Thanks
    5
    Thanked 72 Times in 64 Posts

    Default RS232 Cable Shielding Opinions

    Hi All,
    I am curious what your opinions and recommendations are on where to put the Shield on RS232 cables.

    Here are all the options that I have heard to put the cable shield.
    Pin1 on the DB25
    Pin7(signal gound) on the DB25
    Attach to Housing or outer shell on DB25
    Connect both Pin1 & Pin7 on DB25

    Pin1 on DB25 seems to be somewhat common from what I have seen in documentation. I have seen sometimes where there was issues on the machine and touching the outer shell to the machine has created a small spark. So my thought would to connect to Pin7 would make the most sense as this is signal ground or the reference voltage. However I am not all to sure. Does it make a difference using one shield config over another for longer cables? Are Pin1 and Pin7 generally connected together on the machine side?

    Thanks for your insight and comments!
    Last edited by Petro; 11-07-10 at 01:26 AM.

  2. #2
    Join Date
    Aug 2009
    Location
    Denver Co
    Posts
    18
    Thanks
    0
    Thanked 1 Time in 1 Post

    Default Re: RS232 Cable Shielding Opinions

    Pin 1 is used for shielding, itís also chassis ground.
    Do not attach the shield to both machine and computer. One side or the other should be sufficient. Attaching to both sides on rare occasions has caused problems for me.
    Pin 7 is the UART signal ground only.
    Also if you expect stormy weather, it might be a good idea to disconnect the cable if not in use
    A lighting strike on the building can blow out the UART.

  3. #3
    Join Date
    Apr 2009
    Posts
    132
    Thanks
    0
    Thanked 5 Times in 5 Posts

    Default Re: RS232 Cable Shielding Opinions

    As a no frills set up (2 to 3, 3 ~ 2 jump 4, 6 8, 20 to each other on both ends and tie off the braided shield to pin 7 on one plug only. But doing field service I needed the ready to send clear to send waiting for me and to just minmize any electrial noise more than anything.. A low rent way but I didn't want to spend a lot of time troubleshooting any ul/dl problems.
    But that was cheating and I know it but it worked fine for me no matter the brand of control or machine..
    LOL

  4. #4
    Join Date
    Oct 2010
    Location
    Europe
    Posts
    31
    Thanks
    0
    Thanked 2 Times in 2 Posts

    Default Re: RS232 Cable Shielding Opinions

    Pin 1 on DB25 is connected to the shield. 6-8 to 4 and 20 to 1-6. This is on a 7 wire 25to9-pin cable. Never connect both ends to the shield, as it can give you trouble in the handshake signals, and even error in RTS/CTS signal.

  5. #5
    Join Date
    Sep 2005
    Location
    Wisconsin
    Posts
    996
    Thanks
    5
    Thanked 72 Times in 64 Posts

    Default Re: RS232 Cable Shielding Opinions

    One thing I noticed once was that a customer had a dektop PC hooked up to a machine and when they used there computer it would draw down the voltage through the ground wire of the PC. I actually cut off the ground plug off the PC to prove it. When using my laptop it did not do the same thing. So I am wondering if grounding also makes a little bit of a difference depending on whether a USB to serial device is used verses a serial card in a PCI or PCIE slot or laptop for that matter in regards to grounding and eliminating the amount of electrical noise as well.

Similar Threads

  1. Hydraulic Vise Opinions
    By pa4445 in forum Programming / Applications
    Replies: 3
    Last Post: 09-10-12, 06:22 PM
  2. Doosan CNC Lathes? Opinions wanted!
    By Adtech in forum General CNC & Manufacturing Discussion
    Replies: 5
    Last Post: 08-18-11, 07:58 AM
  3. how to get rid of RS232 com cable?
    By Guest in forum General CNC & Manufacturing Discussion
    Replies: 12
    Last Post: 03-17-11, 08:30 AM
  4. RS232 cable question
    By mykit1 in forum Machine Repair & Troubleshooting
    Replies: 7
    Last Post: 09-05-07, 08:59 PM
  5. RS232 cable compatibility
    By Guest in forum Programming / Applications
    Replies: 12
    Last Post: 02-22-07, 02:21 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •