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For obvious reasons, system migrations vary in size, complexity, and vendor - but without fail, those implementing this taxing process, despite the variety, share a common theme: they must get the plant back to producing as quickly as possible.
Keeping this in mind, most vendors utilize a migration path that is intended to minimize the amount of “rip and replace” that the process requires. Despite the labor and time involved, single vendor migrations are relatively easy. The real challenge, in terms of expediency, exists in the migration between multiple vendor platforms. The path towards migration often originates with parts that have become obsolete or have reached the end of their support life. Conducting a parts survey before a migration plan is established prevents the integration of failure-prone hardware into a new system. Existing relay boards may be one exception as their reuse is perfectly acceptable as long as the individual relays are replaceable and currently available.
Once the parts survey has been completed and obsolete electronics replaced, it is important to confirm that the termination assembly to be converted is a passive device. Over our 30 years in the industry, we've found that an adapter board or custom cable can often serve as a viable solution to the issue of multiple vendor migrations. The adapter board or cable is a passive device that marshals signals from the old I/O termination assembly to accommodate the new I/O cards.
Two key items are necessary to ensure the success of this method. First, it is important to acquire a spare terminal assembly for each I/O type; most plants will have a spare or two they are willing to lend. If spares are not available, then it’s a good idea to locate the documentation from the OEM for each of the termination assemblies to be converted; again, the plant is usually a good source. If all else fails, the internet should be utilized.
Secondly, good documentation for the new hardware’s termination requirements is essential in order to map out the signals from pin to termination and discover where the loop power is originating so that the connector type can be determined. The most common connectors are the IDC type or D-sub, either of which can come in a variety of sizes and genders.
Yet another decision required in the process of integrating multiple vendor migrations involves the board vs. cable debate. This is a question that can be answered by determining the amount of space within existing cabinets. If space is limited, the custom cable will be the ideal solution. Another option would be to add a small cabinet to house adapters.
Alternatively, it is better to use a conversion board when smaller boards need to be combined into a larger one. For example, if two existing eight point analog termination assemblies were slated to be adapted into a 16 point I/O module, a conversion board would prove to be the best option.
For custom cables, a myriad of short run manufacturers exist that will work with the customer on design, removing the need for an in-house PCB expert. It's always a good idea to include spares in the manufacturer’s order, in case of installation damage or for a worst case scenario. There are just as many PCB manufacturers who can meet the the adapter requirement. Personally, I recommend going with Weidmueller or Phoenix Contact because of their extensive experience in this area, as well as their din rail mounting solutions for these boards.
Although the method that I have described here will take a fair amount of engineering, depending on the number of types of signal boards required, the amount of time saved during the conversion process is considerable. In addition, an added benefit is created by excluding any field wiring from the migration process making the loop check out a breeze. By comparing the engineering costs of designing and producing the adapters against the increased installation costs of a traditional rip and replace and its resulting lost production costs, the first option becomes a drop in the bucket.