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| 12/3/2009 3:49 PM | |
Joined: 1/17/2007 Last visit: 4/15/2025 Posts: 1560 Rating:
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Well first of all what type of cable are you using? What is the cable specification (capacitance, conductance etc.). Is the cable screened? Have you ensured that the cable screen is connected to the correct earth nest (signal ground) and connected only at one end? (connecting at both ends can form an earth loop). You could also try pull up / pull down resistors to ensure that the line is driven correctly to idle when not in use. Not sure if the CP already has these or not. The parameterisation certainly has an option to drive the lines to known levels when idle. The following links might prove useful:- RS485 General Info RS485 Cable Info Hope this helps. |
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Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. |
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| 12/7/2009 11:42 AM | |
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Joined: 1/17/2007 Last visit: 4/15/2025 Posts: 1560 Rating:
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Never heard of the GOEKON cable, and I cannot find any reference to it on the internet. The LAN cable you are intending to use should be OK. Basically any good quality twisted pair with overall screen will be suitable. Here is a link to some sutable cable made by Belden. Belden RS485 Cable Note the electrical properties of the cable. These are the important parameters for trouble free communications. |
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Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. |
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| 12/8/2009 12:17 PM | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Joined: 1/17/2007 Last visit: 4/15/2025 Posts: 1560 Rating:
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It is not within the abilities of most individuals to measure cable impedance. Impedance varies with the frequency of the signal travelling on the cable. Impedance measuring is normally performed by the cable manufacturer and provided in the cable specification. In general, I use 120ohm terminators and 470ohm pull-up (bias) resistors. Remember, if using a multi-drop network, only the last 2 devices on the network need terminators. If you stick to these values and use good quality screened cable, you should be fine. Here is some information about cable impedance:- Can I measure the cable impedance using multimeter ?Cable characteristic impedance is a cable characteristics which is only valid for high frequency signals. Multimeters use DC current for resistance measurements, so you can't measure the cable impedance using your multimeter or other simple measurement equipments. It is usually best to check the cable type (usually printed on cable) and it's characteristics impedance from some catalogue instead of trying to measure it. How can I measure cable impedance ?A relationship exists which makes determination of Zo rather simple with the proper equipment. It can be shown that if, at a given frequency, the impedance of a length of cable is measure with the far end open (Zoc), and the measurement is repeated with the far end shorted (Zsc), the following equation may be used to determine Zo: Zo = sqrt ( Zoc * Zsc )Where:
High frequency measurements of Zo are made by determining the velocity of propagation and capacitance of the cable or by reflectometry. Here is some info about general cat5 cable (I am assuming that this is what you are using). Electrical characteristics for Cat.5e UTP
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Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. |
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| 12/12/2009 2:44 PM | |
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Posts: 35 Rating:
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Hi all, The problem not solved...though I try nearly all guide... Anyone who have experiments on this? In fact, who have done RS485 network with more than 400 meters long? the Tx/Rx chip was ADM483EAR as per attachment... AttachmentADM483EAR.pdf (206 Downloads) |
| 12/13/2009 12:25 PM | |
Joined: 10/7/2005 Last visit: 4/17/2025 Posts: 3047 Rating:
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Hello ALU
I haven't, but I wonder if the problem is less related to the cable choice but more to outside interference. In my experience, a RS485 network (or Profibus DP network for that matter) willwork through a pair of wet twisted shoelaces at 9600 bps(Allright, I might be pushing the truth a bit far here, but I think you get the message). To findout how good or bad your signalquality is, you'll need to two channel Oscilloscopeand measure each signal line against 0V (a single channel one will do to, but then you can only measure one of the signal lines at a time). You'll find some good example recordings on what the signal should look like in the Profitrace 2 user manual which you can download fromHERE. Please note that these are Profibus DP Signal Levels (which is based on RS485), but nonetheless will be very similar to what you should see. Apart from that you said that you only connected the shield on one end. I'd strongly suggest to connect the shield on both ends and make surethat you have all devices on the same ground potential to avoid that your shield has to carry anyequalsing current (which will render it pretty useless to protect against outside interference). Attached is a freely available very nice little research paper on this subject. I hope this helps you further and good luck AttachmentThe benefits of applying 61000-5-2 to cable shield bonding and earthing, 21 May 04.pdf (244 Downloads) |
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Cheers |
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| 12/15/2009 9:14 AM | |
Joined: 12/9/2009 Last visit: 4/18/2024 Posts: 156 Rating:
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Hello, I have find the following manuel: http://support.automation.siemens.com/WW/view/en/35222591 There are some generalinformation about PROFIBUS networks (cables, cable length and rate of transmission). Max cable lenght depends on rate of transmission. |
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