PLC IP Address/OPC

einstein_g

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Jul 2018
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I'm very new to PLCs and therefore, OPC. I have a MicroLogix 1000 (Allen Bradley) PLC, which I'd like to connect to an OPC server (KepserverEX) running on my computer.

To connect to the PLC, it obviously needs an IP address assigned, and I need to know what this IP address is.

Do I need to run a DHCP/BOOTP sofware on my PC? Do I need an Ethernet switch in between the PLC and the PC, or an Ethernet crossover cable to connect the PLC to the computer?
 
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Hello Einstein,


Welcome to the forum!


Yes, I believe you will need the software to change the IP address of the device.



No you do not NEED a switch, as long as the IP addresses are within range, you should be able to just connect the two devices. With or without switch.
 
For newcomers to networking i recommend getting an official Cisco CCNA cert guide book (ICND1 100-105). Of course its specific to Cisco switches and routers, but it also does an excellent job of explaining how and why IP addresses and subnets are determined.

Your OPC server needs the IP address of the PLC, wether or not there is a switch between the two is a matter of system physical architecture. Also generally speaking, automation systems generally don't (but not always)use DHCP... they are usually static IP schemes. So, you most likely need to set the static IP on the NIC of the server machine to a unique IP in the same subnet as the PLC.
 
The MicroLogix 1000 does not support Ethernet, only RS232 and RS485. Do you mean MicroLogix 1100? If so you can use the LCD display to find the address assuming someone hasn't set it up so that you can't. Enter the ESC key and then the down button to "Advanced Set" then the "OK" key. Then scroll down (the down button) to "ENET CFG" and then the "OK" button. The IP address should show up.
 
Do I need an Ethernet switch in between the PLC and the PC, or an Ethernet crossover cable to connect the PLC to the computer?

Admittedly, I haven't used a Micrologix before, but I haven't cared about what kind of cable to use (patch vs crossover) since I started my current job (8 years). Auto MDI-X is everywhere, and there's no going back.
 
The MicroLogix 1000 does not support Ethernet, only RS232 and RS485. Do you mean MicroLogix 1100?

I have the MicroLogix 1000, but I have now just obtained access to a 1400 -- any idea whether the 1400 supports Ethernet without having to purchase a gateway/bridge?
 
I have a newbie follow-up question. In my case above, I want to talk to a single PLC through Ethernet via an OPC server.

What about a case where there are multiple (up to 100) networked PLCs, connected to variable frequency drives?

To talk to these PLCs through OPC, is there a device that I'm supposed to connect my computer to, to gain access to the PLC network?
 
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Maybe more details of what you are doing would help

But for the most part, set a (unused) static IP address in your PLC's and the OPC server would look for the address and tags to get your data, can I ask why are you using a OPC server ? are you running a SCADA or HMI or are you just looking to communicate to the PLC? are you using RSLinx as your OPC?
 
I initially just want to communicate with a single PLC via a KepserverEX OPC server.

Eventually, I'd like to looking into getting whatever data I can obtain from VFDs connected to a network of PLCs.

Communicating with a single PLC seems straightforward -- I can just connect the PLC to my computer via an Ethernet cable.

I'm just not sure how I would communicate with individual PLCs in a network of many PLCs i.e whether I need to connect to this network via an intermediary device.
 
As long as they are on the network and have the correct IP address (you also) you should be able to connect using RSLinx for programming

I have used Kepserver in the past for a couple applications and its not that bad to setup and get running the HMI I was using was RSView, I also had a RSView app with RSLinx OEM as the OPC and both ran good

What is your app that you need the OPC?
 
It depends. You have to elaborate a bit more on what your intentions are.

For example, you mentioned OPC but saying OPC doesn't tell us what it's used for. Is it used to serve a HMI or talk to another system or device?

Speaking in general. You talk to a specific PLC by setting up a pointer of some kind. In OPC, it's generally called a TOPIC. A TOPIC points to a specific device in an OPC server. A device sit under a CHANNEL. A channel configs the port and protocol.

To tell your program to talk to a PLC the format is in the form of :

OPC Server-Topic

Topic consists of Channel and Device.
 

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