Dear all,

Good day.

I would like to seek for opinion regarding Profibus network connection.

I used ET200M (IM153-2) as slave and connected to Optical Link Module (OLM) via Profibus.

Is it still required to connect from OLM to Profibus terminator?

I will really appreciate anyone's opinion.

Thanks and Best regards

Hello Newbae;

To add to mopSO4's answer, here is an illustration of termination requirements for the electrical (copper) section of a OLM circuit.

This is taken from the OLM manual, which you should keep close-by when you are working with fiber optic connections.:

SIMATIC NET Network components/PROFIBUS Optical link module (OLM) - Operating Instructions

https://support.industry.siemens.com/cs/ca/en/view/109476821

Hope this helps,

Daniel Chartier

Thanks for answering my query. I very much appreciate it.

Also, I would like to ask if Profibus Terminator (i.e. 6ES7 972-0DA00-0AA0) is still required to be connected after the OLM.

Sorry, I didn't understand well the usage of Profibus terminator.

Please see the attached file for the sample configuration.

Thanks and Best regards

Hello Newbae;

I have looked at your sample configuration, and I have a few questions.

First, let's discuss the Profibus active terminator.

This module (6ES7972-0DA00-0AA0) is an alternative to the termination resistor that is built-in to the standard Profibus connectors. It is clear that termination must be provided at both ends of the Profibus network, if not the bus will see reflexions on the cables and the network will crash. But it is important to realize that these termination resistors are powered by the end-nodes, and that is power is removed from these nodes then it is as if the termination resistor was not present. You might remove power to a node for maintenance purposes, for example, or cleaning in certain industries. As an alternative the active termination resistor can be connected next to one (or both) of the end-nodes, with its own 24 VDC power, and will provide termination on the bus even if the end-node is unpowered or removed. 

Basically, where you need termination, use the Profibus connector terninating resistor (as is usually done) or an active bus termination (if the situation requires it).

The attached screenshot comes from the Profibus networks manual:

https://support.industry.siemens.com/cs/us/en/view/1971286

Second, and this is just a detail, the second rack you show is a redundant Y-link, comprised of 2 redudndant IM 153-2s and one Y-coupler (not a Y-Link, as you show). This will allow you to connect a non-redundant PLC to the redundant Profibus interfaces of the S7-400H.

Third, your schematic shows no useful implementation of the OLMs (Optical Link Modules). These fiber-optic transmitters extend a copper Profibus segment over fiber-optic cables, so they work as pairs ( copper--> fiber-optic --> fiber-optic--> copper). Open the diagram I proposed earlier, you will see that every OLM is connected to (at least one) other OLM using fiber-optic cable, and each one is also connected in turn to a copper Profibus segment with PLCs or ET 200 stations.

That way, a master PLC will connect to the OLM with copper cable, the fiber optic cables will link 2 OLMs, and the second OLM will connect through copper to a Profibus slave. Transparently, the master PLC will send and receive Profibus transmissions to its slave, without realizing that there is a section of fiber-optic cables in the segment.

So your diagram either is incomplete, or needs reworking...

Hope this helps,

Daniel Chartier

dchartier

Hello Newbae;

I have looked at your sample configuration, and I have a few questions.

First, let's discuss the Profibus active terminator.

This module (6ES7972-0DA00-0AA0) is an alternative to the termination resistor that is built-in to the standard Profibus connectors. It is clear that termination must be provided at both ends of the Profibus network, if not the bus will see reflexions on the cables and the network will crash. But it is important to realize that these termination resistors are powered by the end-nodes, and that is power is removed from these nodes then it is as if the termination resistor was not present. You might remove power to a node for maintenance purposes, for example, or cleaning in certain industries. As an alternative the active termination resistor can be connected next to one (or both) of the end-nodes, with its own 24 VDC power, and will provide termination on the bus even if the end-node is unpowered or removed. 

Basically, where you need termination, use the Profibus connector terninating resistor (as is usually done) or an active bus termination (if the situation requires it).

The attached screenshot comes from the Profibus networks manual:

https://support.industry.siemens.com/cs/us/en/view/1971286

Second, and this is just a detail, the second rack you show is a redundant Y-link, comprised of 2 redudndant IM 153-2s and one Y-coupler (not a Y-Link, as you show). This will allow you to connect a non-redundant PLC to the redundant Profibus interfaces of the S7-400H.

Third, your schematic shows no useful implementation of the OLMs (Optical Link Modules). These fiber-optic transmitters extend a copper Profibus segment over fiber-optic cables, so they work as pairs ( copper--> fiber-optic --> fiber-optic--> copper). Open the diagram I proposed earlier, you will see that every OLM is connected to (at least one) other OLM using fiber-optic cable, and each one is also connected in turn to a copper Profibus segment with PLCs or ET 200 stations.

That way, a master PLC will connect to the OLM with copper cable, the fiber optic cables will link 2 OLMs, and the second OLM will connect through copper to a Profibus slave. Transparently, the master PLC will send and receive Profibus transmissions to its slave, without realizing that there is a section of fiber-optic cables in the segment.

So your diagram either is incomplete, or needs reworking...

Hope this helps,

Daniel Chartier

 Hi Sir Daniel,

Good day.

Thanks for detailed explanation. I understand it more clearly.

For the sample configuration I showed, sorry for the confusion. I did not complete the configuration properly. The OLM is connected to another OLM and connected to Y-Link Coupler via (same with the connected Y-Link Coupler in the first OLM). This will come up as Copper > fiber-optic > fiber-optic > copper as you also said.

I would like to ask if separate Active Terminator (i.e 6ES7972-0DA00-0AA0) will be required to connect after the first OLM. Because when I refer to OLM manual, the connected Profibus connector to OLM should be switched ON.

Thanks and Best regards

Hello Newbae;

Termination is available to you on every Profibus connector, simply switch the Terminator switch ON or OFF as needed. Power for the terminator will be provided by the node the connector is attached to.

You need an active bus terminator only on those end-nodes that you expect power will be cut on a regular basis, in regular operations. Remember that a terminating resistor must be powered at all times to maintain the integrity of a Profibus network; if you will need to disconnect or regularly power down a Profibus slave that happens to be an end-node,  then you can start thinking of active bus terminations. But it is exceptional.

An example we worked on: a milk plant where we integrated a Profibus network needed daily wash down to keep entry and exit bays bacteria free. This means that every evening high power hoses would be used in areas that included our end-nodes for cleaning. Operators would remove power from the PLC cabinets (designed for water ingress protection) to make sure no electrical problem occurred. We integrated active bus terminators at the beginning and end of every Profibus segment (with their own separate 24 VDC power) so that other nodes on the network would still continue communicating even when the wash down forced an end-node to be powered down.

Hope this helps,

Daniel Chartier