Need Profinet explanation please

[BeepBob]

Hello all,

A little background. Our organization is exploring using the Siemens S7 1500 PLCs in the future. We are an Allen Bradley's house.

Just had a session with a Siemen's engineer and I am still a little uncertain.


Here goes:

1. As I understand it, from Allen Bradley, using RSLinx you can create a driver to browse all devices on a specified subnet. The subnet need not be the one your workstation is currently on. This works great.

2. We are looking to do this same procedure with TIA Portal and it seems like TIA Portal cannot browse devices (PLCs, Remote IOs, Drives etc..) outside of the local subnet (Siemens calls it network).

It seems like Profinet will not go out to another subnet using a Layer 3 device and look for devices.

Question: So does this mean that I can't have a PLC on one subnet lets say 192.168.2.x and a remote IO on say 192.168.3.x talk to each other? Without having to resort to a Profinet to Profinet coupler card?

Allen Bradley can do the above all day I think starting with version 25 and above with RsLogix 5000. And this is the current setup for a small subset of our scada network.

What if I want to link 80 remoteIOs in the field to my brand new S7 1500 sitting on my desk on a different subnet?

 

[Puddle]

IP address is made up of two halfs, first half is the network, second half is the address. This means that 192.168.1.1 is on the same network as 192.168.3.1*

You'll need three 1500's if you want to link 80 remote IOs though, maximum is 32**

*Never tried this myself though. I may try this on my test bench later to satisfy my own curiosity.

**May be wrong there, a new generation of CPUs was launched with TIA v18 earlier this year, they may have increased the connection limit but I don't have that manual to hand.

 

[BeepBob]

IP address is made up of two halfs, first half is the network, second half is the address. This means that 192.168.1.1 is on the same network as 192.168.3.1*

You'll need three 1500's if you want to link 80 remote IOs though, maximum is 32**

*Never tried this myself though. I may try this on my test bench later to satisfy my own curiosity.

**May be wrong there, a new generation of CPUs was launched with TIA v18 earlier this year, they may have increased the connection limit but I don't have that manual to hand.

You're right, it is on the same network. I should be more clear, it needs to be on the same subnet for Profinet to see devices. I'm exaggerating with 80 remote IO. But shoot now that you mentioned maximum 32, I gotta go back to the drawing board, I missed that info.

 

[JesperMP]

You mention both SCADA and remote IO.

A SCADA connect to an S7 PLC in the same way as any other networking device. It is pure TCP/IP, it is not 'Profinet'. So the SCADA can exchange data with an S7 PLC if it can reach it. If the SCADA and PLC are on different networks, there must be a router in between.

Regarding the remote IO, you mention different subnets, but not if the subnet mask is adapted to include both subnets (i.e. the subnet mask is 255.255.0.0). If the subnet mask is adapted, a PROFINET IO Controller with 192.168.2.x can control a PROFINET IO Device with 192.168.3.x

I ask why is there a need to place the remote IO on different networks ?
I would definitely not mix the control network of the machine or plant with other networks, and that for several reasons. One reason is that if the machine network is directly part of a larger network, then IT will step in and demand to control everything. And from my onw experience, ITs demands gets increasingly more restrictive every year.

 

[Puddle]

I would definitely not mix the control network of the machine or plant with other networks, and that for several reasons. One reason is that if the machine network is directly part of a larger network, then IT will step in and demand to control everything. And from my onw experience, ITs demands gets increasingly more restrictive every year.

Most of my automation equipment is using the company network, but all the IT stuff is on subnet 255.255.255.0 and mine is 255.255.254.0. IT will not use a different subnet and actually told me it couldn't be done.

I tell them when I add a new device so there's no conflicts and we've not had a problem yet. Luckily they're not very intrusive and I don't think it's like that in most companies.

 

[JesperMP]

The maximum number of Profinet IO Devices depends on the CPU.
For example a 1511 can control 32 Profinet IO Devices.
A 1515-2 can control 64 Profinet IO Devices.
A 1508S (which is a software PLC) can control 256 IO devices on one port or 384 IO devices total if using multiple ports.

 

[BeepBob]

You mention both SCADA and remote IO.

A SCADA connect to an S7 PLC in the same way as any other networking device. It is pure TCP/IP, it is not 'Profinet'. So the SCADA can exchange data with an S7 PLC if it can reach it. If the SCADA and PLC are on different networks, there must be a router in between.

Regarding the remote IO, you mention different subnets, but not if the subnet mask is adapted to include both subnets (i.e. the subnet mask is 255.255.0.0). If the subnet mask is adapted, a PROFINET IO Controller with 192.168.2.x can control a PROFINET IO Device with 192.168.3.x

I ask why is there a need to place the remote IO on different networks ?
I would definitely not mix the control network of the machine or plant with other networks, and that for several reasons. One reason is that if the machine network is directly part of a larger network, then IT will step in and demand to control everything. And from my onw experience, ITs demands gets increasingly more restrictive every year.

Ahh yes, I meant that my workstation that hosts the TIA Portal software will be on a different subnet than the S7 and the remote IO.

As to why the remote IO is on a different subnet than the PLC. I have no idea as it was before my time. And unfortunately our group doesn't manage the the OT network and its associated network hardware. I wish we do.

Oh i gotta see if TIA Portal lets user apply a subnet mask.

Anyone here use TIA Portal like what i described above?

 

[JesperMP]

You can definitely program an S7 PLC from a different network, even over the internet. There must be a router that provides the connection between the networks.

Our machines usually have max 20 IO devices. No need to split into different subnets. But we have multiple networks and machines, and we tend to split the networks, then interconnect them with NAT routers. In that way one machine can be shutdown without affecting other machines.
This is a huge topic actually.

 

[busarider29]

Just curious as to why you're considering moving to Siemens?

 

[mk42]

The maximum number of Profinet IO Devices depends on the CPU.
For example a 1511 can control 32 Profinet IO Devices.
A 1515-2 can control 64 Profinet IO Devices.
A 1508S (which is a software PLC) can control 256 IO devices on one port or 384 IO devices total if using multiple ports.

My look at the tech specs says a 1511 can have 128 IO devices on the integrated PN interface, and then up to 256 total via expansion.


Maybe you were looking at 32 distributed IO systems? that means up to 4 PN/DP networks (integrated or CM/CP) and then the rest connected in via proxys, Asi, etc.

 

[JesperMP]

My look at the tech specs says a 1511 can have 128 IO devices on the integrated PN interface, and then up to 256 total via expansion.


Maybe you were looking at 32 distributed IO systems? that means up to 4 PN/DP networks (integrated or CM/CP) and then the rest connected in via proxys, Asi, etc.

I stand corrected.
You are absolutely right.
I was looking at the wrong entry in the data sheet.
So a measly S7-1511 can control up to 128 Devices !

 

[mk42]

Ahh yes, I meant that my workstation that hosts the TIA Portal software will be on a different subnet than the S7 and the remote IO.

As to why the remote IO is on a different subnet than the PLC. I have no idea as it was before my time. And unfortunately our group doesn't manage the the OT network and its associated network hardware. I wish we do.

Oh i gotta see if TIA Portal lets user apply a subnet mask.

Anyone here use TIA Portal like what i described above?

So just to check, PLC and IO will be in same subnet? then yay, that's the biggest concern.



You can define IP address, subnet mask, and gateway for your PLC and IO devices.


You can program the PLC from another subnet, as long as the networking is set up correctly. That could mean either proper gateways are defined and in place, or NAT is available. When you go to do the download, you try a "Show all devices with the same address" (which tries to directly access the PLC via IP) instead of the default of "Show all compatible devices" which scans the local network to see if the PLC happens to be there.



The network scan concept for Profinet has nothing to do with IP addresses. Literally IP address isn't even in the discovery message. You can detect/rename/see any PN device on the local network you are plugged into. If your Laptop with 192.168.12.34/255.255.255.0 is plugged into your automation network, with devices in the range of 192.168.100.X/255.255.254.0, you'll still see them and be able to reassign device name/IP/etc.


You won't be able to scan any of the devices, even if your laptop is in the correct IP range, if you're trying to scan from your desk.


Also, many of the S7-1500's (S7-1515 and up) come with at least two Ethernet networks built in. One is a two port switch that supports full profinet capabilities, and the other is a 1 port interface that can be an extra IO network, but is usually used for uplink to a factory network. That might simplify the networking discussion.

 

[mk42]

I stand corrected.
You are absolutely right.
I was looking at the wrong entry in the data sheet.
So a measly S7-1511 can control up to 128 Devices !

I ran into comms limitations on 300's all the time, it was frustrating. The 1500's blew those limitations away, and now any time I have comms limitations, I look to see where my architecture went wrong vs immediately getting grumpy about the PLC.

Well, except there's no good way to get high speed data logged into an HMI, but that's a separate issue.

 

[BeepBob]

You won't be able to scan any of the devices, even if your laptop is in the correct IP range, if you're trying to scan from your desk.


.

So coming from the Allen Bradley world, I link all devices into my project from my workstation at my desk, because I can just add the devices to my project using IP addresses. And once I write to the PLC , the PLC knows to go out and talk to the field devices.

If I cannot scan field devices from my workstation at my desk, How do I add them to the project? Do I need to take my workstation and put it onto the same subnet as those Remote IO to add them to my project?

Maybe I gotta reread the training, because the training video only shows adding new devices after you scan for them.

 

[mk42]

So coming from the Allen Bradley world, I link all devices into my project from my workstation at my desk, because I can just add the devices to my project using IP addresses. And once I write to the PLC , the PLC knows to go out and talk to the field devices.

If I cannot scan field devices from my workstation at my desk, How do I add them to the project? Do I need to take my workstation and put it onto the same subnet as those Remote IO to add them to my project?

Maybe I gotta reread the training, because the training video only shows adding new devices after you scan for them.

Ok, lets take a step back. What are you trying to do? What's your situation? Does your PLC and IO exist yet?


If no, you can create it manually in TIA by dragging objects in from the HW Catalog on the right side.


If the IO already exists and is configured (assuming it is Profinet IO), then you CAN do the above, or you can plug into the automation network (Programming Ports on PLC cabinets are traditional almost everywhere I've been) and then do a scan, and import them.



This whole thread is a little hard to follow (and this isn't a knock on you in any way), because subnet CAN mean a group of IP addresses, and it can also mean a section of a physical network. IN THEORY, these should be one and the same (no devices anywhere else in the network with IP addresses in that range and all devices in that network in that range), but in practice they can be different. I want to make sure we aren't confusing the concepts.


Profinet works at the MAC address layer (layer 2) for IO control and device discovery. The discovery protocol will find all devices on the local network, which is usually all the devices it can talk to without having to go through a router. Your IP address is mostly irrelevant, where you are plugged in is what matters.