If you read Part 1 then this article expands on a real-life example as to WHY you need to ensure the equipment you purchase, doesn't lock you into a path from which you can't recover, or will cause you unnecessary grief in the future.
Consider this scenario:
- You purchased equipment from a vendor and didn't ask any of the questions outlined in part 1, particularly the one about access to the source code of the equipment
- At some future time you wish to integrate the equipment into your 'smart factory'
- You ask the vendor to make a software change for you, that being a modification to the PLC IP address(es), to get the equipment onto your new factory LAN
- You discover that the vendor has actually created their own subnet, downstream of the PLC, which connects to whole range of their kit, such as VSDs, HMIs, SCADA PCs, other PLC remote I/O etc and also to a remote access gateway (like an EWON) that the vendor utilises for remote support
- The vendor, who's now overseas, points out that they cannot change the IP address of the PLC since that would put it on a different subnet to the rest of their kit, and therefore the whole line would become inoperable.
What to do?
- You could change all the IP addresses, re-test all the machine communications and ensure it all works, but you'd need to have software access to all the other kit as well, not to mention the downtime and RISK
- You can put in a second Ethernet module (if PLC rack space permits) and configure it to be on the factory LAN, but you don't have access to the PLC to configure it, so you have to ask the vendor to do it all for you
- You can get your IT department to purchase a managed switch, install and configure it so that the LAN-side is on the factory subnet while the downstream-side is still on the equipment's subnet, so it acts as a network address translation gateway
Or you can simply ask those 11 questions, up front and save yourself this future grief!
Remember, you're responsible for what you purchase and you probably expect a long life from your investment, so why not get it right the first time?
John Broadbent; Realise Potential
