Multiple communication protocols

Hi,
I am wondering if anyone could help me!!! This may be an obvious question that i am missing the point to but its worth asking.

I am creating a new system using a micrologix 1200 or maybe a slc5/04 both are available if needed.The system is communicating with a platform scale, 3 loss-in-weight feeder and a barcode scanner which all communicate using ASCII protocol.

The question-- is there a way of using different protocols on the same network?

We need to use some sort of a DH485 network using AIC converters which can communicate in ascii but the data acquisition software and pannelveiv we have use a DF1 protocol.

Any help and information on how to do this would be of great use. Are we using the correct converter,protocols ect.

Thanks in advance.

Others may have more experience, but generally RS232 devices are 1 per channel. The micrologix only has one serial port, and there is no way i am aware of to add additional ports. You can use the SLC with a 1746-BAS card, but they are not cheap or easy to set up. IMO, the simplest solution would be a CompactLogix L2x or L3x with 1769-ASCII modules. You get 2 ports per card and setup is not too bad.

You cannot easily mix protocols on a serial network of any sort.

That's one of the reasons that Ethernet and TCP/IP are so great; the underlying transport is the same and you can mix application-level protocols. You're probably running ten different application protocols right now in the background while browsing this webpage.

But when the transport is slow and simple like RS-232 or RS-485, you're really limited to one protocol.

A MicroLogix 1200 would be over-burdened with two HMI/Data clients plus five ASCII devices. You might even find that the ASCII devices don't like seeing each other's traffic on a network.

I agree that modular communications would be the way to go. If it were me, and I was planning to use an SLC-500 family controller, I would use an SLC-5/05 with a 1747-SDN and individual DeviceNet/ASCII interface modules. But that's my preferred platform and may not be your preference.

Thank you for both of the reply's. They have been much needed help.
The micrologix 1200 and the slc 4/05 are currently available for use but that does not mean that they have to be used.

A follow on question then would be, is there a PLC better suited for our application?

Ken you have stated that you would use a slc 5/05 with an 1747-SDN and individual DeviceNet/ASCII interface modules. Have you stated this because in my original question i mentioned that a slc 500 family controller was available or is it because you would of chosen that for the application because it would be the 'best' for the job?

i am not familiar with Ethernet and TCP/IP protocols but that dosent mean that i am not willing to learn.Would this be better suited to our application?

The reason for using different protocls at the moment is because the loss-in weight feeders, scales ect only have an rs232 port available and we understand how to communicate with them using ascii.

Nothing is set in stone but any further advice or tips would be greatly apreciated.

Thanks

I would modify Kens statement to "You cannot cheaply mix protocols on a serial network of any sort". I have done something similar to what you need by using DeviceNet as a "backbone" with a serial module for each device. This could be done with the SLC if a scanner is fitted. If you only need to use a single command (i.e. read data) for each item then this message can be hard coded into the serial module and the PLC only needs to trigger it as required. I have used Escort Memory Systems CM11 modules which can be field mounted without the need for panels but the PointIO modules are just as good if you have an enclosure to mount them in.

If this is a new system, I would still highly recommend the CompactLogix system. SLCs are QUICKLY becoming obsolete, and their pricing is rising even faster. CompactLogix would be cheaper, easier to implement, and you wouldn't have to deal with DeviceNet (which can cause major headaches), and supported longer. Only downside is you would need to purchase RSLogix5000 if you don't already have it, but even with that added expense, it would still be cheaper than a SLC and DeviceNet.

Helliana said:

If this is a new system, I would still highly recommend the CompactLogix system. SLCs are QUICKLY becoming obsolete, and their pricing is rising even faster. CompactLogix would be cheaper, easier to implement, and you wouldn't have to deal with DeviceNet (which can cause major headaches), and supported longer. Only downside is you would need to purchase RSLogix5000 if you don't already have it, but even with that added expense, it would still be cheaper than a SLC and DeviceNet.

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I assumed that the SLC was an existing PLC as I could not imagine anybody buying a 5/04 for a new project (even if they are still available). Whatever you use, however, you still need multiple serial ports to handle the different protocols.
We have dozens of DeviceNet networks with hundreds of nodes in our plant and these have never caused us any major headaches. Some of our DeviceNet systems have been in operation for more than 15 years without any problems other than replacing the occasional faulty device. The key to this is always proper installation. That said I only gave DeviceNet as an example because that is what I have used in the past. Any fieldbus system which has serial modules available would work just as well.