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Proper disconnecting of Profibus slaves

Created by: Hawk1 at: 3/16/2010 12:45 PM (13 Replies)

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3/16/2010 12:45 PM	Rate (0)
Hawk1 Posts: 8 Rating: (0)	Hello, in my machine there is S7-300 CPU and about 10 slaves on Profibus DP. It's the press and the tool inside connected via Harting connector. On the tool there are some slaves (ET200S) and this tool can be disconnected and totally removed from the press. My question is, how should I design the network (what special devices should I use). I'm sureit's not OK when I just disconnect the profibus cable at the tool - I would expect errors on the whole network because of not proper termination of the bus. Does RS485 repeater help? Remark: I would like to achieve 12Mbit speed. Thanks for any advise.
Hawk1 Posts: 8 Rating: (0)
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3/16/2010 1:51 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 9/14/2025 Posts: 12408 Rating: (2717)	Hellow Hawk; As long as the Profibus slave is part of the master's configuration, it will be accessed cyclically, and yes, there will be faults on the bus if you disconnect it. If the removal of the slave is temporary, you could use SFC 12 'D_ACT_DP', which de-activates a slave so the master does not call it; you therefore remove the irritant that causes BF and SF LEDs and disconnect the slave. You can use SFC 12 one acgain to re-activate the slave when required.See the following FAQ: http://support.automation.siemens.com/WW/view/en/17624225 If the removal is permanent, it would be advisable to change the master's Profibus-DP configuration and download it anew. Hope this helps, Daniel Chartier

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3/16/2010 2:14 PM	Rate (0)
Hawk1 Posts: 8 Rating: (0)	dchartier Hellow Hawk; As long as the Profibus slave is part of the master's configuration, it will be accessed cyclically, and yes, there will be faults on the bus if you disconnect it. If the removal of the slave is temporary, you could use SFC 12 'D_ACT_DP', which de-activates a slave so the master does not call it; you therefore remove the irritant that causes BF and SF LEDs and disconnect the slave. You can use SFC 12 one acgain to re-activate the slave when required.See the following FAQ: http://support.automation.siemens.com/WW/view/en/17624225 If the removal is permanent, it would be advisable to change the master's Profibus-DP configuration and download it anew. Hope this helps, Daniel Chartier Thank you for reply, Daniel. I've already heard about SFC12, but I think I mustfirstsolve the "hardware problems". The tool in my press will be time to time exchanged for another one. And meanwhile the press must be working even without any tool present. So the press resp. the network will be sometimes without the slaves on the tool and if I just disconnect the Profibus line, the network won't beproperly terminated (physically). Then even if I deactivate the slaves on the tool there will be errors on the disconnected network because of some reflections or whatever...
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3/16/2010 5:08 PM

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dchartier

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Hello Hawk;
Ahh, it wasn't clear to me that what you needed was a proper and permanent terminaton of the bus. And yes, removing the termination while the bus is powered will wreak havoc on the bus controller...
So one option is to use an externally-powered termination module after the last node on the bus, such as this one:

6ES7972-0DA00-0AA0

SIMATIC DP, RS485 RESISTOR FOR TERMINATING PROFIBUS-/MPI-NETWORKS

Open the link to the A&D Mall, and look for the Description tab. You should get more information on the product and its design. You will need to bring 24 V DC power to the module, which can be a fuss if the distance is large, but whenver we have set it up we have lived happily with disconnecting Profibus nodes; although without SFC 12 you will still have alarmLEDs on the master when you remove any node, the rest of the bus will still work without a hitch.
Hope this helps,
Daniel Chartier

3/17/2010 7:03 AM	Rate (0)
Hawk1 Posts: 8 Rating: (0)	Hello Daniel, thanks for replaying. You can look at the attached schematic drawing of my profibus DP network, just for imagination. I'm not sure if therepeaters on the scheme are the right solution. When the tool from the press is removed, both connectors XC21 and XC22 are disconnected. So I need to disconnect part of the profibus, not only one node. In this case I don't know where should I place the RS485 termination resistor you've suggested Now on the drawing both ends of the profibus are on the tool (+WZ1U resp. +WZ1O). But even if I continue with the profibus line back through the XC21 resp. XC22, then after disconnection of these connectors the profibus end would be cut out as well from the rest of the network... I hope it's alittle bit clearer for you now. Attachment my profibus network.jpg (532 Downloads)
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3/17/2010 8:37 AM	Rate (0)
gfair Posts: 37 Rating: (0)	Are +WZ1O and +WZ1U Racks on the same tool? If so, can you not make a profibus connection between them so you won't require terminating resisitor.
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3/17/2010 9:22 AM	Rate (0)
Hawk1 Posts: 8 Rating: (0)	+WZ1O and +WZ1U are actually two separate parts of the tool (upper and lower part) and it's not possible toconnect them directly to each other. Each half of the tool is connected to the press separately.
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3/17/2010 4:44 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 9/14/2025 Posts: 12408 Rating: (2717)	Hello again Hawk; Thank you for the schematic, it explains a bit more of your problem. we faced something of the kind in our plants, when we had to connect Profibus-DP slaves that did not have a sub-D connector, and needed to be removed from the network on irregular or unpredictable sequence, for repair or maintenance; these were mainly valves and flowmeters on a piping system. The solution we finally implemented was based on Weidmuller T-connectors for Profibus-DP. Look at the following thread (last post contains product information): /tf/WW/en/Posts/37171 You can also look at the following product presentation to see how this T-connector works: http://www.voltimum.co.uk/news/12954/cm/weidmuller-profibus-dp-distributor-designed-for-use-with-steel-wire-armoured-cable.html The particular model illustratrated here is for steel-armoured Profibus cable, designed for harsh environments, which could be useful in your machine setting. But we used other models, for standard cabkle, with or without integrated termination. Basically, you use the T-connector to create a spurline (as short as possible) to which your slave will be connected. The main Profibus-DP trunck continues to the next slave, so that when the spurline is disconnected the network is not affected (although diagnostics will still be called for that missing slave). Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 3/17/2010 4:44 PM
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3/18/2010 4:15 AM	Rate (0)
gfair Posts: 37 Rating: (0)	ah. OK. You could make a terminal box with a D9 connector on it's front. Inside the box have a few terminals and a resistor for termination. Solder the wiring to the D9 and use as a termination point. When you remove the tool, plug the profibus cable into new D9 box and it will terminate the cable for you. This might work.
gfair Posts: 37 Rating: (0)	Last edited by: gfair at: 3/18/2010 4:17 AM
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3/18/2010 10:56 AM	Rate (0)
Hawk1 Posts: 8 Rating: (0)	Hello gfair, it's even more complicated We've already used the variation of yoursuggestion on some machinesin the past. But I haven't mention that in this case the Harting connectors are connected automatically by the pneumatic cylinder and are out of reach of the operator. So the operator has no access to terminate somehow the profibus line. I would need something which allows me to disconnect the part of the network on the tool withoutrequirement of any setting of anything by operator. Maybe I need too much Hello Daniel, the spur line would be at least one meter long (from Harting connector on the tool to the ET200S on the tool). And also I haven't mentioned that in the future there can be anothertool with more Profibus slaves on it. Anyway I would like to use the network on 12Mbit/s if possible. And any spur lines are not recommended from Siemens when usinghigher speeds...
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3/18/2010 9:51 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 9/14/2025 Posts: 12408 Rating: (2717)	Hello Hawk; One last detai I forgot to mentionl at 1,5 MB total spurline length can be 6.6 meters. In our casewe used many spurlines, so we had to limit each one to about 20 cm. But for one or 2 on the bus, 1 m should not affect. If you must run at 12 MB, then I agree that spurlines could induce trouble on the bus. But I have no other solution ready, and I do know that engineering often requires compromise between maximum performance and security... But that is your decision. Hope it goes well for your project, best of luck, Daniel Chartier

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3/19/2010 4:38 AM	Rate (0)
gfair Posts: 37 Rating: (0)	Hawk1 Hello gfair, it's even more complicated We've already used the variation of yoursuggestion on some machinesin the past. But I haven't mention that in this case the Harting connectors are connected automatically by the pneumatic cylinder and are out of reach of the operator. So the operator has no access to terminate somehow the profibus line. I would need something which allows me to disconnect the part of the network on the tool withoutrequirement of any setting of anything by operator. Maybe I need too much ... Why don't you wire the profibus cable through a relay that is energised from a binary output. The normally open contacts is used for the ET200/ cylinder and the normally closed for a terminating resistor. When the tool is present the cable is made to the ET200/ cylinder and when it is removed the cable is terminated. You need to modify your program to add the binary output for every job thathas the tool present. Attachment 2010-03-19 Terminate.jpg (370 Downloads)
gfair Posts: 37 Rating: (0)	Last edited by: gfair at: 3/19/2010 4:59 AM Last edited by: gfair at: 3/19/2010 4:41 AM Last edited by: gfair at: 3/19/2010 4:41 AM Edited for spelling
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3/20/2010 2:55 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 9/14/2025 Posts: 3049 Rating: (1062)	Hello Hawk1 gfair's suggestion could in principle work, watch out for two things things though: 1.) The termination must be an active one (5V -> 390Ohm resistor -> B line -> 220Ohm resistor ->A line -> 390 Ohm-> 0V) 2.) The relay must be able toessentially seamlessly switch over from one to the other, otherwise you will leave yourself "vulnerable" to experience short bus instabilities(especially at 12Mbit/s). The already dicussed idea of using repeaters in a way that you have only one device attached to it is the one I would personally opt for and perhaps Procentec'sProfihub could be of use for you in this case. I hope this helps
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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3/22/2010 3:14 AM	Rate (0)
gfair Posts: 37 Rating: (0)	fritz Hello Hawk1 gfair's suggestion could in principle work, watch out for two things things though: 1.) The termination must be an active one (5V -> 390Ohm resistor -> B line -> 220Ohm resistor ->A line -> 390 Ohm-> 0V) 2.) The relay must be able toessentially seamlessly switch over from one to the other, otherwise you will leave yourself "vulnerable" to experience short bus instabilities(especially at 12Mbit/s). The already dicussed idea of using repeaters in a way that you have only one device attached to it is the one I would personally opt for and perhaps Procentec'sProfihub could be of use for you in this case. I hope this helps i think there would probably be a downtime in changing out the tool and as the realy is software driven could be achieved readily.
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Proper disconnecting of Profibus slaves

Created by: Hawk1 at: 3/16/2010 12:45 PM (13 Replies)

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Created by: Hawk1 at: 3/16/2010 12:45 PM (13 Replies)

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