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Technical Notes
Connecting Virtual I/O Modules to PLCs on Different Networks
By Adisa Shaljani
Product: DeltaV Virtual IO Module - VIM2

The purpose of this technical note is to show how the DeltaV Virtual IO Module Network Gateway allows communication to PLCs across different networks.

The DeltaV Virtual IO Module (VIM) Network Gateway can communicate to PLCs that reside on different networks as long as they have a common subnet mask. The different subnet masks on the same network will also keep devices from talking to each other. Knowing the IP address of key network components such as routers, servers, bridges, and all other network devices can be useful when connecting them to interface with each other. Use of utilities like Ping or Trace Route can assist user in determining whether devices can reach each other.

Selecting an IP Address

When the VIM is used to interface between the DeltaV and the PLCs that are on different subnets and different networks, the user can pick either IP address. In the VIMNet Explorer user will specify the IP address and subnet mask for each VIM as shown in Figure 1:

Figure 1: Configuring IP address and Subnet Mask in VIM-Net Explorer

For example, if the PLC 1 is configured with the IP address 10.22.6.x and PLC 2 is configured with the IP address 10.22.7.x the VIM can be configured with either the IP address 10.22.7.x or 10.22.6.x as long as the subnet mask throughout the network are 255.255.252.0 or wider 255.255.0.0. for a non-consecutive third octet.

Selecting Common Subnet Mask

This step is crucial for healthy communications between devices on different networks. The subnet mask defines the relationship between the host (computers, routers, switches, etc.) and the rest of the network devices. For the devices on the same network, the recommendation is to configure them with the same subnet mask. For devices that reside on different network it is recommended to use open subnet mask that doesn’t filter out the broadcasts from any device on the network. As shown in the Figure 2 below, the sub-net mask of 255.255.0.0 will allow devices on networks with IP addresses 10.22.x.x. and 10.22.y.y to converse with each other.

Figure 2: VIM connected to two different networks

Summary

The DeltaV Virtual IO Module Network Gateway allows communications across the different networks. There are some subnet rules that need to be followed but overall it’s very flexible and scalable.