Hi Everyone,
We are using DeltaV 12.3 with VIM2 cards for modbus. We are planning to have a couple of complex slaves, and in quite a lot of cases, only one slave will be on a VIM card.
For these, we would like to simplify the network by having a point-to-point connection, a single Ethernet cable with one end in the VIM card and one end in the slave. Would you recommend against this?
To set the VIM configuration, we would temporarily connect a switch, insert a laptop with VIMNet Explorer, configure the card and then remove both the switch and the laptop.
Does this seem to be a workable solution?
Thanks,
Istvan
In reply to István Orbán:
Istvan,
Someone from Emerson asked a very similar question to MYNAH Technologies on November 18th so I suspect this may be the same implementation. I would just like to reiterate the gist of MYNAH's response.
It is possible to use the VIM with a point-to-point connection. Tom is right to be wary about using this configuration. When you use the point-to-point connection you are hampering a lot of the benefits of Modbus TCP and limiting your diagnostics capability. At the very least we at MYNAH Technologies always suggest using at least a single switch between the two devices.
1. With a point-to-point connection you are limited to only receiving diagnostics from DeltaV. You would not be able to run live diagnostics on the VIM using VIMNet Explorer Diagnostics which is what MYNAH uses to diagnose more complicated communication problems. It's better to use the switch if only to create an access point for a laptop with VIMNet Explorer at start-up rather than taking the system offline to add it.
2. In the case where there are multiple point-to-point VIMs, the network may be conceptually simple, but the management becomes much more complex. VIMNet Explorer can manage multiple VIMs, in this scenario, multiple VIMNet Explorer configurations would be necessary. Going point-to-point removes this central management capability.
3. The Simplex Modbus TCP VIM is able to communicate with up to 32 devices over Ethernet. When you use a point-to-point connection you are needlessly limiting this capability. If any expansion occurs in the future, the customer will need to remove the point-to-point connection and add a switch anyway.
4. Finally, the redundant port on the VIM is used for sharing the connection status between VIMs. While the connection will fit, this port cannot be used as a second Ethernet port and diagnostics information cannot be extracted from this port.