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PLC - Device Communications--Question for the Community

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Hello, people  :)


I am curious...

You've got your PLC.

You've got your I/Os, barcode readers, frequency converters...a whole universe of devices. 

You've got to get them talking...


What is your preferred protocol? Which do you find is the easiest to set up and use?

Is there one that you really love :wub:​ ...or really hate  :wacko:

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I think the way to phrase this is what com protocols do I have to use regularly as compared to what would I like to use.  Given my industry type (and being in Oklahoma USA) most equipment I have to interface to comes standard with Mobdus RTU 485/232 and some has Modbus TCP.


From a generic standpoint we use the following (in order of frequency):


RS485 modus to most VFDs and soft starts

UNICAN talking between PLCs

CANBus J1939 for engines and valve controllers

Modbus TCP/IP to talk to Allen Bradley equipment

BACnet for building BMS

Lonworks for building BMS


No one has asked us to use Profibus but I am sure it will happen sometime.




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As a note on what Keith says about Profibus.

The V130,V350 and the new V430 can act as profibus slave but not as a profibus master so it,s not possible to connect

I/O of other devices directly to one of these controllers using profibus.

Another protocol that is more commonly used in europe besides profibus is profinet.


So if Unitronics controllers will be considdered in plants in Europe to do small tasks and theirfore have to communicate with Siemens controllers esspecially the Profinet protocol should be considdered I think? 




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Hello Cara


Why not offer an OPC client interface for the Unistream like most scada systems already have?
With the Vision systems Unitronics offered an OPC server so that scada systems can communicate in that way with Unitronics PLC, s.
In  practice al major OPC server manufacturers have a OPC server that can communicate with all important brand plc,s
If for example Unistream could act as a OPC DA client it would be quit easy to interface it with all kind of other brand plc,s and make use of the Unistream as kind of a scada system that also has the advantage that it can run plc logic.

The Unistream  has the potential to be used as scada  especially in combination with the intergrated web server and in this way it would not only compete with PLC manufactures but also with scada manufactures.


This is just a personal Idea.


Kind Regards


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Well Cara,


What I would like to use is a magical protocol that does all of the work automatically on its own just by my connecting one device to any other device, but since C3PO/R2D2 are still not a viable technology (COMON WORLD :D ) I will just have to continue to do it the hard way. 


Seriously the only com that I get asked for that an enhanced Vision does not do is Ethernet/IP.  I know that Unistream will have this worked out soon (if not already), but it would still be most excellent to have it in a Vision controller as well.



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  • 1 year later...
  • 2 weeks later...

- RS-485/232 custom protocol - for digital scales, barcode scanners, etc.

- CANopen - for distributed I/O modules

- MODBUS TCP/IP - connecting multiple Unitroncis PLCs together

- MODBUS RTU - for various slave devices, VFDs, etc

- MODBUS ASCII (very rarely) - Rinstrum weighing indicators, and other exotic devices


I wish there was a 4-port or 8-port I/O module with integrated protocol FB.

For example: "IO-4RS2-2RS4" with 4xRS-232 and 2xRS-485 port. Configure protocols via FBs or hardware configuration.

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