enggvijay
Electrical
- Nov 21, 2011
- 3
we r using profibus and ethernet cable for communication purpose.i know that profibus is a two wire communication while ethernet is a multiwire, but what is the main difference between this two?
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why can we not use profibus and ethernet cable instead of each other? 2
- Thread starter enggvijay
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This is too important to just paste a link.
Taken directly from
Michael Garnham
October 2010
Did you know that you cannot use just any sort of cable (including scooby wire!) for your PROFIBUS DP (Copper) installation? Did you know that it has to be a cable specifically designed for PROFIBUS? Maybe you already do, in which case, maybe another thread would be of more interest to you, but for those of you who are operating PROFIBUS networks without any formal training, then stick around and you will possibly find out what has been the reason for those dreaded middle-of-the-night callouts.
We at the PCC (PROFIBUS Competence Centre) are being called out to numerous sites that are having PROFIBUS trouble and we are finding one of the most fundamental rules of PROFIBUS is being broken, that being, the wrong cable is being used. The operators of these networks are not even aware of this.
“What should I be looking out for?” PROFIBUS DP cable is purple. However, just because your cable is purple, it doesn’t necessarily mean that it is PROFIBUS DP cable. The cable should be made up of a purple outer PVC coating (which normally says PROFIBUS DP cable on it), a stranded shield (for high frequency noise), a foil shield (for even higher frequency noise), a strengthening substrate, and finally two coloured cores (red and green).
You also get cable that is specifically made for PROFIBUS PA. A blue one is used for PA in Intrinsically safe environments and a black one is used for non-intrinsically safe environments. These cannot be used on DP.
Use the stranded core variant for places with vibration or movement – just keep in mind that fast connector plugs can only be used on the solid core variant.
“My plant has been running fine for years, why the sudden issues?” It’s true. PROFIBUS networks can run for a very long time on the wrong cable before they give any trouble, especially if you are running your network at a low baud rate. The trouble is that your network may be operating just within the tolerable thresholds of operation, when a change in the environment (temperature changes, voltage spikes, noise, etc) causes the network to suddenly fall over.
Interested in the science stuff? Well, a PROFIBUS DP cable has an impedance 150 Ohm (unlike conventional RS-485 cable which is at 120 Ohm). The impedance of the cable changes drastically at the end of the cable and the signal energy travelling down the cable finds nowhere to go an gets reflected back (reflections). Reflections can cause multiple signals to appear, corrupting the original signal. This is why we insert terminations at each end of the cable – they absorb this excess signal energy. PROFIBUS devices and plugs with built in terminators have had their terminators designed to match the cable impedance. When you use the wrong cable, the impedance is no longer matched and reflections occur.
Okay, that's it for now. Do leave any comments or questions that you may have. In the mean time, I hope this helps someone out there!
Michael Garnham
PCC
Taken directly from
Michael Garnham
October 2010
Did you know that you cannot use just any sort of cable (including scooby wire!) for your PROFIBUS DP (Copper) installation? Did you know that it has to be a cable specifically designed for PROFIBUS? Maybe you already do, in which case, maybe another thread would be of more interest to you, but for those of you who are operating PROFIBUS networks without any formal training, then stick around and you will possibly find out what has been the reason for those dreaded middle-of-the-night callouts.
We at the PCC (PROFIBUS Competence Centre) are being called out to numerous sites that are having PROFIBUS trouble and we are finding one of the most fundamental rules of PROFIBUS is being broken, that being, the wrong cable is being used. The operators of these networks are not even aware of this.
“What should I be looking out for?” PROFIBUS DP cable is purple. However, just because your cable is purple, it doesn’t necessarily mean that it is PROFIBUS DP cable. The cable should be made up of a purple outer PVC coating (which normally says PROFIBUS DP cable on it), a stranded shield (for high frequency noise), a foil shield (for even higher frequency noise), a strengthening substrate, and finally two coloured cores (red and green).
You also get cable that is specifically made for PROFIBUS PA. A blue one is used for PA in Intrinsically safe environments and a black one is used for non-intrinsically safe environments. These cannot be used on DP.
Use the stranded core variant for places with vibration or movement – just keep in mind that fast connector plugs can only be used on the solid core variant.
“My plant has been running fine for years, why the sudden issues?” It’s true. PROFIBUS networks can run for a very long time on the wrong cable before they give any trouble, especially if you are running your network at a low baud rate. The trouble is that your network may be operating just within the tolerable thresholds of operation, when a change in the environment (temperature changes, voltage spikes, noise, etc) causes the network to suddenly fall over.
Interested in the science stuff? Well, a PROFIBUS DP cable has an impedance 150 Ohm (unlike conventional RS-485 cable which is at 120 Ohm). The impedance of the cable changes drastically at the end of the cable and the signal energy travelling down the cable finds nowhere to go an gets reflected back (reflections). Reflections can cause multiple signals to appear, corrupting the original signal. This is why we insert terminations at each end of the cable – they absorb this excess signal energy. PROFIBUS devices and plugs with built in terminators have had their terminators designed to match the cable impedance. When you use the wrong cable, the impedance is no longer matched and reflections occur.
Okay, that's it for now. Do leave any comments or questions that you may have. In the mean time, I hope this helps someone out there!
Michael Garnham
PCC
- Thread starter
- #3
The premium for the correct cable, engineered specifically for Profibus, is peanuts in the cost of any project. A real advantage of Profibus is that it's an engineered solution, and when Profibus components are used, Profibus works and works and works.
Profibus analyzers are in the $5k category. The guy who has one and knows how to use it doesn't come out and troubleshoot a problematic installation for nothing. His minimum charge to show up on-site with his analyzer is probably 10x the difference between the cost of Profibus cable and the cost of whatever cable. Why tempt fate?
Profibus analyzers are in the $5k category. The guy who has one and knows how to use it doesn't come out and troubleshoot a problematic installation for nothing. His minimum charge to show up on-site with his analyzer is probably 10x the difference between the cost of Profibus cable and the cost of whatever cable. Why tempt fate?
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