Skip to Content

SiePortal

The integrated platform for your product selection, buying and support workflow - bringing together Industry Mall and Online Support.

SiePortalDeutsch

Search

Home
Support Support
{{(apiData.Support | filter:{'rank':1}:true)[0].title}} Support
- Menu temporary not available
- Menu temporary not available
- Menue temporary not available
- {{item.title}}

Products & Services
- Menu temporary not available
- Menue temporary not available
- {{item.title}}
Support Support
{{(apiData.Support | filter:{'rank':1}:true)[0].title}} Support
- Menu temporary not available
- Menue temporary not available
- {{item.title}}
MySiePortal MySiePortal
{{(apiData.MySiePortal | filter:{'rank':1}:true)[0].title}} MySiePortal
- Menu temporary not available
- Menue temporary not available
- {{item.title}}
Cart ({{apiData.CartCount}})

Navigation

Profibus DP termination resistor query

Created by: Nklai at: 6/5/2015 1:18 AM (3 Replies)

Rating (2)

Thanks 3

4 Entries

6/5/2015 1:18 AM	Rate (0)
Nklai Posts: 3 Rating: (0)	Hello everyone, I have a query regarding the termination resistors of the Profibus DP arrangment indicated in the attached simplified network topology. Quick explanation of the topology: 2 racks, each including 1 x 317-2 DP CPU and 1 x CP342-5 communications processor. The two communciations processors are linked via Cu/FO (via OLMs). Each CPU has its own MPI and Profibus DP network which go to other systems (these systems are not indicated on the simplified drawing). Please take a look at the red squares. They indicate termination resistors on bus connectors that are ON. The yellow square indicates a termination resistor on a bus connector that is OFF. I'm almost certain that this resistor should be ON. Can someone confirm this? Please note that this connector indicated in yellow has only one bus cable going into it i.e. it's the end of that particular branch. From my understanding, you need to terminate both end of the lines otherwise you're setting yourself up for reflections taking place. The reason that I'm querying this on this forum is that I've just joined a new plant and found that they have been experiencing a lot of PLC comms fault glitches for years. Due to this fact, I am a bit wary of changing anything from the way that it has been operating for years in case something weird and wonderful happens. Any help much appreciated! Cheers, Nick Attachment Simpified topology.JPG (324 Downloads)
Nklai Posts: 3 Rating: (0)
Suggestion To thank Quote Answer

6/5/2015 10:59 PM	Rate (1)
Online Tech Platinum Member Joined: 3/28/2015 Last visit: 2/15/2025 Posts: 722 Rating: (214)	Nklai I have a query regarding the termination resistors of the Profibus DP arrangment Please take a look at the red squares. They indicate termination resistors on bus connectors that are ON. The yellow square indicates a termination resistor on a bus connector that is OFF. I'm almost certain that this resistor should be ON. Can someone confirm this? Hello, Terminating resistor is ON at both ends in order to avoid signal reflection. The terminating resistors should be ON in your attached simplified network topology.
	Eng.Mohamed Ibrahim WhatsApp : +201122880543
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users Nklai

6/6/2015 2:54 AM	Rate (0)
Nklai Posts: 3 Rating: (0)	Online Tech Nklai I have a query regarding the termination resistors of the Profibus DP arrangment Please take a look at the red squares. They indicate termination resistors on bus connectors that are ON. The yellow square indicates a termination resistor on a bus connector that is OFF. I'm almost certain that this resistor should be ON. Can someone confirm this? Hello, Terminating resistor is ON at both ends in order to avoid signal reflection. The terminating resistors should be ON in your attached simplified network topology. Hi there... Thanks very much! I'm not a complete beginner with these things but, because I have just arrived at this plant and this arrangement that I mentioned has probably been like that for a looooong time (probably years), I was really starting to question myself. Thanks again! Much appreciated.
Nklai Posts: 3 Rating: (0)
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users Online Tech

6/8/2015 6:38 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 3/23/2025 Posts: 3042 Rating: (1061)	Hello Nklai on the subject of "I am a bit wary of changing anything from the way that it has been operating for years in case something weird and wonderful happens": Please check how long the cable is between the OLM and the CP342-5. While the advise by Online tech is of course correct and each Segment mus be terminated on either end, there can be situations where this could make it worse rather than improve the situation. The general rule is that you should always have at least 1m of Profibus cable between two neighbouring stations (be that station a DP Master, DP Slave, OLM, repeater etc.). This 1m of cable decouples the two stations from each other so that the capacitive mismatch each station creates does NOT add up and creates undue reflections. This 1m rule will also hopefully one day soon make it into the official Profibus guidelines. If you have only two stations on a Segment though (as is the case here), you are best adviced to have at least 2m of cable installed between the two. If not (and assuming both terminators are on as they normally should be), you can end up "over terminating" the Segment which may the reason someone decided to NOT have the terminator on at the CP342-5 (and while this 2m rule is generally accepted best practice, you won't find it in any official documentation). 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.
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users Online Tech

|

Share this page:

Share this page on...

Follow us on