What is best, an S7 CPU with PN or a seperate CP341?

Marshy · Oct 22, 2008

Hi,

I have a job which I'm looking in to which requires 7 PLC's which will be on mobile conveyors (S7200) and 1 PLC (S7300) that has to communicate with all 7 conveyors and 1 Gem500 over modbus.
All PLC's will communicate over ethernet.

We were orginally going for a CPU 315-2DP with a CP343-1. The CP343-1 would be used to communicate with a HMI, a Gem500 PLC over modbus tcp, and 7 x S7 200 CP 243-1's.

I haven't used Profinet module before so my question is, could we just use a CPU 315-2 PN/DP and do away with the CP343-1? Are there any disadvantages in doing this?

Also after reading Jespers post about the IM 151-8 we're considering using them instead of the S7200.

Any thoughts would be appreciated,

Cheers

seppoalanen · Oct 22, 2008

I don't ever use PN/DP cpu.
There is only S7-Connection possibility.
No multi- or broadcasting capability.

mday · Oct 22, 2008

I would go with the S7-315-2 PN/DP

The S7-315-2 PN/DP will work fine in your application. PROFINET is just one of the protocols you can use with either the built in PN port or a CP343. For your application you will need Modbus/TCP, and S7 communcations over Ethernet, both are supported with the onboard port. It's also less money too.

seppoalanen · Oct 22, 2008

I don't know there in US, but here total prise is very equal.

Marshy · Oct 22, 2008

seppoalanen said:
I don't know there in US, but here total prise is very equal.

Thanks for the replies

Price is one of the reasons we're looking into this option:

CPU 315-2 DP £1,076 + Cp341-1 £1,045
CPU 315-2 DP/PN £1,712

Because we like to keep spares as well we'd end up saving around £600

seppoalanen · Oct 22, 2008

Was it CP 343-1 Lean, 6GK7 343-1CX10-0XE0 ?
Sounds expensive..

Marshy · Oct 22, 2008

seppoalanen said:
Was it CP 343-1 Lean, 6GK7 343-1CX10-0XE0 ?
Sounds expensive..

the cp 343-1 Lean is £594, however it won't work with modbus tcp and is limited in its number of connections.
The order number for the one I quoted earlier was 6GK7343-1EX30-0XE0

JesperMP · Oct 23, 2008

You absolutely must check this webpage that seems to tell it all.
http://www.industry.siemens.de/IT4Industry/EN/solution_services/SIMATIC_Addons/proto_mod.htm
It lists exactly which CPUs will work with Modbus TCP, and what software package you need. It looks like both CP343-1 LEAN and IM151-8PN will work with Modbus TCP.

I want to know what they charge for the Modbus TCP libraries.
Also, I wonder if Modbus TCP uses any connection resources.

Apart from that, I use a lot of 315-2PN/DP's and I am quite happy with them. Quite capable if not extremely performant.

JesperMP · Oct 23, 2008

About disadvantages of PN CPU as opposed to CP343-1.

Generally the ethernet performance is much better.
However, the CPU performance is decreased because the main CPU must handle the ethernet comms by itself in stead of letting the CP do the job. Then again, this should only be an issue if the amount of ethernet comms is very large.

Marshy · Oct 24, 2008

JesperMP said:
You absolutely must check this webpage that seems to tell it all.
http://www.industry.siemens.de/IT4Industry/EN/solution_services/SIMATIC_Addons/proto_mod.htm
It lists exactly which CPUs will work with Modbus TCP, and what software package you need. It looks like both CP343-1 LEAN and IM151-8PN will work with Modbus TCP.

Yes you're right, I messed up there, I was looking at another job at the same time, and that S7 has to communicate with an S5-135 on ISO which the Lean model didn't support.

I'm still not sure the Lean Model would be able to communicate with 8 PLC's, a HMI and a programming device at the same time?

JesperMP said:
I want to know what they charge for the Modbus TCP libraries.Also, I wonder if Modbus TCP uses any connection resources.

Apart from that, I use a lot of 315-2PN/DP's and I am quite happy with them. Quite capable if not extremely performant.

I found out the price today, and its pretty high - £1415!

Cheers

JesperMP · Oct 24, 2008

Does Modbus TCP use any connection resources ?

Jeebs · Oct 24, 2008

Marshy said:
I found out the price today, and its pretty high - £1415!

Cheers

I don't know where you're shopping, but thats a ripoff.

We paid 400-500€ for our libraries.

And yes Jesper, it uses connection resources. Same as any other TCP connection would.

Marshy · Oct 24, 2008

Apparently its Siemens List Price?

Marshy · Oct 27, 2008

I'm a bit confused about whether we can use the Lean version or not:

Here it says only 4 S7 communication links can be made. If I were to use ISO on TCP then the lean version would be okay, is that right?
I also can't seem to find anything which says the advantages of using S7 communication over ISO on TCP connections?

Cheers

JesperMP · Oct 27, 2008

It says in the flyer for the Modbus TCP library, that AG_SEND/AG_RECV is used for the CPs, and that the "T" blocks are used for the PN CPUs.

I think that the CP343-1 LEAN is not enough for your application.
With the HMI + Gem Modbus TCP + 7xS7-200/IM151-8 + ? you need something with at least 9 connections.
I would go for the 315-2PN/DP and 7xIM151-8PN. The 315-2PN/DP has 14 connections on its PN port.
Between the 315-2PN/DP and the IM151-8, I would setup S7 connections.

What is best, an S7 CPU with PN or a seperate CP341?

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