PLC and SLC difference

rrangaprasad · Apr 18, 2005

Hey i know this is a silly question for most of you guys. But i'm new in this area.

what is the difference betweeen a PLC and SLC?\

thanks
ranga

rrangaprasad · Apr 18, 2005

PLC connected to SLC and modem

The reason i am asking is that in my example,

a PLC/5 is connected to modem and SLC.
Why does a PLC need to talk with SLC or modem? or what could be the reason for this connection?

i know its vague.
But any help w'd be great

mgvol · Apr 18, 2005

The PLC-5 uses octal-based addressing, while the SLC is 16-bit. As for why they are connected, I assume that there is a need to exchange data between the processes they are each controlling. The modem is probably for dial-in troubleshooting/monitoring.

jolio ST · Apr 18, 2005

Hmm..I've pondered about this problem before. But I was thinking that both are models from the Allen-Bradley family. Differences between them: Not much. Programming wise: PLC uses RSLogix 5 and SLC uses RSLogix 500.
But I saw this article written by Ron, and he is Brilliant!

I should think it is what you might seek. (Thank you Ron!)

regards
Sherine T.

rrangaprasad · Apr 18, 2005

question

here is the thing:

A PLC, like i've mentioned before is connected to a SLC and modem.
They are for the same process.

From what i gather, SLC could be used for modular-centric purposes, etc. My question is as it is the same process, what is the purpose of using an SLC? Can't PLC do all the work of an SLC.

And DF1 is just a protocol just like DH+, right?

PS: I am a Mechanical Engineer and that why ..........

ranga

mgvol · Apr 18, 2005

Does the SLC rack have its own CPU? If not, they are simply using it as remote I/O for the PLC-5. Yes, DF1 is a protocol (RS-232, Null-Modem). Yes, the PLC can do the work of a SLC, but it is lower-cost (much lower), so many people use SLC I/O as a remote I/O rack to save money.

rrangaprasad · Apr 18, 2005

modem

Thanks. And no. they don't have CPU in them. That makes sense.

Now i'm guesssing SLC and PLC can be connected by DF1, right? Why does the modem come in the picture?

thanks for the info.
the more i learn from every reply that i get

ranga

mgvol · Apr 18, 2005

So the modem is connected BETWEEN the PLC and the SLC? What is the first module in the SLC rack? Is it a 1747-ASB? If so, they are connected as remote I/O and I don't know what the modem is for. Are you sure it is a modem, or could it be an A-B KF2 interface?

jolio ST · Apr 18, 2005

If it is a modem, mayhaps it is for communications to another network, say Scada for one. and connected between the 2 PLC devices ensures data is circulated among 3 or more sources.

rsdoran · Apr 18, 2005

You need to define the specific layout. If the modem is connected to the PLC5 then it can be used to program troubleshoot the system. The SLC (without CPU) racks can be used as remote I/O with many systems including a PLC5. IF the SLC rack is remote I/O then the PLC5 will have all the addresses etc in its program so anyone using the modem can troubleshoot any part of the system including what is being used in the SLC rack.

PLC and SLC difference

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