Migration or one-by-one replacement?

Two factors which are often taken into consideration when replacing (outdated) control systems include the condition of the control panel and the availability of reserve materials. It also goes without saying that budgets must be taken into consideration.

If a customer chooses to retain the existing control panels and just replace the PLC hardware, we can then ask whether the existing software programs need to be transferred one by one, or whether these need to be rewritten. The second of these options is known as migration and comprises replacing the existing PLC configuration with a new one, potentially developed by another manufacturer, as well as rewriting the software.

Moekotte Enschede B.V. has built up extensive expertise in the field of implementing and providing consultancy services in relation to migration projects, such as from Siemens S5 to Siemens S7. This expertise is not of course limited to Siemens migrations, but also extends to Allen Bradley, Schneider, Mitsubishi and Beckhoff migration projects.

Due to the fact that Siemens no longer supplies its S5 products, Moekotte has replaced a large number of existing Siemens S5 systems with S7 controllers. This involves the following processes:

• Conversion of the S5 code to S7 code using the Simatic Manager.
• Migration of S5 to S7, during which the S7 code is rewritten.

The latter option is preferable, as it prevents errors in the existing software from being copied automatically, whilst enabling comments to be included in the software and allowing for standardisation. In order to do this, Moekotte uses standard software building blocks that have been constructed in accordance with the ISA-S88 standard. The benefit of this is that it gives rise to a standardised model that, by virtue of its structure, is easy to maintain and develop.

Practice has taught us that the replacement of S5 systems with S7 often needs to be carried out within a short timeframe. As a result of this, the software building blocks offered by Moekotte come inclusive of simulation tools. that enable a dry run of the PLC software. In addition, the company uses simulation packages (including WinMod and Pics) that allow the current situation in the customer’s production process (motors, valves, instruments) to be imported into the simulation package. The new software can be fully tested by creating a link between the PLC software and the simulation package, allowing for a practical simulation of the scenario in the field (faults, reports etc.). This gives rise to much a shorter lead time during the introduction of the software: the operators can get accustomed to the new software, prior to its implementation, and the customer can rest assured that, after it has been implemented, the new software will work perfectly.