S7-300 Distributed IO

[Ross_A]

Hi, I'm supposed to be designing some panels which will use a S7-300 CPU in one location which needs to receive signals from distributed IO from remote panels (9 off) which are scattered around the factory. Now, i've been sort of left to it (everyone is working away), so i'm sat here wondering how to do it (i've just started as a trainee control systems engineer). Now i remember the boss (on holiday atm) saying something about using the ET200M, so i looked it up on the siemens website and within the manual it seems to refer to the numbers IM 153-1/2. Could someone explain how to use these please? I know that i need 4 off AI cards (8I), 1 off DI card (16I) and 1 off DQ card (16O) in each remote panel, so that's the IO the Interface Module will have to deal with. Any help given much appreciated. Regards, Ross

[JesperMP]

Hi Ross. The IM153-1 and IM153-2 are modules that allows you to setup remote Profibus racks with S7-300 i/o modules. Siemens calls this system ET200M. So, to setup a project with these you create a project in the STEP7 HW Config with a CPU that has a DP port (S7 315-2DP for example), set the DP port to be "networked", select the Profibus network that is assigned to the DP port, and then add an IM153-1 from the HW Catalog, and finally add the i/o modules to the IM153-1 from the HW catalog. This is described in chapter 2.5 in this manual: http://support.automation.siemens.com/WW/view/en/1142798

[Ross_A]

Thank you for the explaination Jesper. For my installation there will be 8 IM153-* in remote enclosures, so how would i figure out which variant to use? Do i need an additional IM module in the main PLC enclosure to receive connections from the remote IM modules? Thank you again, Ross

[JesperMP]

Hi again Ross. Pick the IM153-1 for the remote slaves. Apart from that I recommend that you chose a CPU with an onboard Profibus DP port (like the mentioned 315-2DP). This is simpler, cheaper and better than adding a Profibus module (CP342-5) in the central rack.

[Ross_A]

Thank you again. Sorry, but i am very new to control engineering and PLCs (2 weeks infact) so i'm struggling a bit. I think i understand what you mean now though. I was looking at the ET200M manual and i noticed in the accessories that it mentions a PROFIBUS cable with bus connector. Is this how the slaves will be connected, in a 'daisy chain' method where one slave is linked to the next and then finally back to the CPU? Thanks, Ross

[JesperMP]

Yes. It is a daisy-chain. The CPU doesnt have to be at the end. It can be in the middle if this suits the cabling better.

[Ross_A]

Oh that makes sense now. I was thinking that the CPU would have to accept 8 connections, for some reason i was thinking of a star topology with the CPU being the central node, when of course it's a PROFI'BUS' topology. I'll start to understand this eventually.. (i hope) I've also read that a termination resistor is required when using a RS-485 technology, do you know how to implement this or shall i just search with google? Ross

[JesperMP]

Standard Profibus connectors allows two cables to be fitted. A switch on the connector disconnects one of the cables AND connects integral termination resistors.

[Ross_A]

Ah, i just saw on a website about the swtich on the connector for the terminating resistor (PROFIBUS Connector datasheet). I thought the value of the resistor had to be equal to the impedance of the cable used to stop reflections of the signal occuring. Is the resistor in the connector a fixed value, or is it variable, or can it be interchanged? Thanks!

[Groo]

Fixed