View Full Version : Slc 500 1747-dcm

February 6th, 2011, 12:21 PM
Haven't found the anwser here or in the AB documentation.
Does anyone know how many DCM modules can be placed in a SLC rack?

I have 4 production lines running, I have started adding Idle timers to shut conveyors down, how ever the Plant manager wants to add a button to cycle stop each line from a remote location.

Since each line has an RIO network connecting each processor in the Line, I figure I can get a supervisor PLC (it will be a controls logic processor).
Add a DCM module (all lines have SLC's)and daisy chain the 4 lines.

I'll send a stop signal to the lines either collectively or individually over this network and then use the lines RIO network to do the actual shut down.

Thanks for the help

Ken Roach
February 6th, 2011, 02:14 PM
First be sure the 1747-DCM is still in production. I know its 1771 counterpart was discontinued a few years ago.

Unless you have a very large set of extended chassis, you shouldn't worry about the memory used by a 1747-DCM; it can transfer only 2 to 8 Words, about the same as an Analog module. The SLC backplane data table is 256 Words each of Input and Output data.

Power consumption has to be determined for any 1746 I/O structure; RSLogix 500 includes a quick power calculator or you can do it by hand.

Ken Roach
February 6th, 2011, 02:15 PM
Since each line has an RIO network connecting each processor in the Line

Take a step back and re-examine that. Are you sure it's not a Data Highway Plus network between SLC-5/04 controllers ? The cable used for DH+ is identical to that for RIO and it's easy to get them mixed up. The port into which the cable is connected will tell you what it's used for.

February 6th, 2011, 02:59 PM
The set up is that I have an RIO scanner in one rack and the other cotrollers on line are slaves to it.

We use DH+ (connected at the processor) primarily for connecting to the PLCs and passing info such as blocked, starved, faulted. I/O info passed between controllers such as interlocks are passed over the RIO network.

Thanks for info

February 6th, 2011, 03:53 PM
If you have DH+ already why add more RIO? Just use the existing comms

Ken Roach
February 6th, 2011, 04:27 PM
Thanks for explaining in more detail; I understand better now that you have an existing RIO-based co-ordination network and want to add another one in parallel.

RIO might be ancient (I've read the original 1977 design documents) but it's reliable and simple.

Here's an idea just to toss out there: does the I/O table you are using now with the 1747-DCM's have enough room in it to handle the cycle stop bits ?

What I'm thinking is that you could put in a 1756-RIO (not a 1756-DHRIO) in the ControlLogix in Adapter Mode, and have the existing SLC "master" read the cycle stop commands from it, then forward that cycle stop data to the existing 1747-DCMs.

This would add a couple of RIO scans and at least one SLC program scan to the timing of these cycle stops, but it would not require the addition of another run of RIO cable or a new 1747-DCM in each chassis.

February 6th, 2011, 06:19 PM
Corp standards have designated DH+ for information only, sort of a low level SCADA, PM&C, FIS setup and RIO for I/O interlocks or any other "discrete" I/O, line speed regulation.

I thought about the connecting into the existing RIO, however, there is desire to keep each line seperated, plus I have some future plans I'd like to incorp, and this seems like a good way to get some one else to pay for the major components I want to add in.

February 6th, 2011, 10:32 PM
Sounds good to me. We have some systems still running 5/02 with the DCM.

AFAIK it's still on the market, and rock solid in my experience. Ours uses some pretty simple multiplexing to get about a dozens words transferred every three seconds using the DCM as RIO from 4 SLC 5/02s to a PLC-5/40.