Schneider Electric has replaced an ageing programmable logic controller with a modern unit in record time.

The installation at Northcombe Water Treatment Works in Somerset was finished within a single plant shutdown period of eight hours.

While able to meet the current requirements when installed in the 1980s, the Modicon 984-685 PLC now had little spare I/O capacity and no free program memory.

But the PLC was so vital to operations on the site that it could not be out of commission for more than eight hours.

One option was to install a new PLC alongside the old one, and to migrate the systems to the new machine over time. But the process would have been both lengthy and costly.

Schneider Electric proposed a radically different solution. It would assemble a new PLC which would be physically interchangeable with the old one, and which would use the same input/output (I/O) wiring.

This was made possible by using Schneider Electric’s upgrade adaptors, which convert field wiring intended for older Modicon PLCs so that it is compatible with the I/O systems used by the latest Modicon Quantum Series products.

Schneider Electric carried out much of the preparation work away from the site, including full assembly and testing of the new I/O racks.