Control Systems How to Facilitate Re-use of Field Wiring in Control System Upgrades

Editor: Dr. Jörg Kempf

Since its introduction in 1979, the Simatic S5 PLC-based control system has penetrated many areas of the process industries. Although many installations are still working reliably, however, in 2003 Siemens began to phase the system out. Faced with the prospect of an eventual lack of spares and support, many users are upgrading to the more powerful Simatic S7 system. System cabling solutions from Phoenix Contact aid rapid and straightforward migration from S5 to S7.

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The S5/S7 adapter is located between the S7 module and the S5 front connector. (Picture: Phoenix Contact)
The S5/S7 adapter is located between the S7 module and the S5 front connector. (Picture: Phoenix Contact)

Although spare parts for the Simatic S5 control system will be available for years to come, this will be only on a replacement basis, since Siemens is no longer developing the system. The range of services and support available for S5 will also decrease in due course.

Newer systems such as the Simatic S7, on the other hand, offer some significant technological advantages. As users facing increasing competition in international markets demand higher productivity from their machines and processes, it is therefore no surprise that users are migrating from Simatic S5 to S7.

To keep downtimes short, many users adopt a phased approach to migration. The new system is often configured in parallel to the existing one, and switched over once everything has been tested offline. A fallback strategy typically allows the operator to revert to the old system if things do not go as planned.

This migration involves both software and hardware, the latter including not just PLCs, operator terminals and engineering workstations but also cabling and I/O, both local and distributed. However, not everything may need replacement at the same time. While the average life of the PLCs and terminals is 14 years, I/O modules provide useful service for up to 20 years, and field wiring can be used for 30 years or more. As a result, many users opt to keep their existing field wiring during the upgrade.

Keep Existing Field Wiring

Phoenix Contact has developed solutions that save time and money by simplifying the process of migrating from Simatic S5 to S7 and allowing existing field wiring to be re-used.

Adapters provide both a mechanical and an electrical interface between the existing S5 front connectors and the new S7 modules. Neither the conductors nor the terminals of the field wiring need to be disturbed.

A wide variety of adapters is available to suit the numerous S5 and S7 module types. This system has been used successfully across the full range of S5/S7 applications, including steel plants, cement plants and high-bay warehouses.

Variants of these adapters known as commissioning adapters also simplify the process of checking that the new system will operate exactly as planned. Commissioning adapters extend the existing S5-115U or S5-135U wiring by several meters, providing a free end that can be connected to the new S7 system.

First, the new S7 controller is placed in a temporary location in front of the existing control cabinet. Next, the front connector is removed from the existing S5 controller and replaced by the commissioning adapter. The S5 front connector is then plugged into the commissioning adapter. Finally, the free end of the commissioning adapter cable is connected to the new S7 module.