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APACS System Migrations Overview

Over the next few blogs, we will be examining the migration options and methods used by various control system vendors. The benefits and limitations will be discussed based on experience gained over the previous 15 years of implementing each migration option. This document is intended to provide specific details regarding the Siemens Moore APACS and QUADLOG system while the merits of the target systems mentioned are well documented in the respective vendor manuals.

There are many reasons and criteria used in the selection of a control system when a migration is required. System preference, familiarity, support, and ease of use are a few, but for the purposes of this document we will be looking at the following,

  • Controller Only Solution – connect to existing I/O cards
  • Hybrid system capability and ease
  • Connection to existing I/O terminations
  • Connection to existing HMI

The “Controller Only” solution refers to the ability of the new system to connect directly to the existing APACS I/O cards. At this time, one vendor has this in place. There are always limitations to this approach. In this case they are the ability to change the I/O configuration post migration and additionally I/O diagnostics are not supported. This means that the I/O configuration is basically fixed and unused channels would not be available without a shutdown of the new CPU. If I/O diagnostics were deemed a requirement they would have to be configured manually in the new CPU logic.

The “Hybrid System Capability” refers to the ability of the existing APACS system to pass control system data to/from within the migrated system without the need of an additional interface. This is an important consideration during a phased approach to migration where some of the APACS areas may be converted at different times.

“Connection to Existing I/O terminations” refers to the ability to connect the existing FTA’s to the I/O cards of the migration system. With one exception, all other vendor solutions will require some additional engineering and custom wiring harnesses to connect the APACS I/O to the migration system. The FTA’s and new I/O cards are not typically “one for one”, or a direct swap. A custom wiring harness is usually required to connect a single FTA to multiple I/O cards in the new system. In addition, a majority of the APACS I/O cards do not support channel to channel isolation and share a common instrument ground.  

Connection to existing HMI is a consideration during a phased approach where the original HMI will run in parallel to the new system. This is dependent on the capabilities of the current HMI but most will require an additional OPC interface to keep this functionality.

Note that in all cases, the QUADLOG safety system does not allow for controller only, or connection to existing I/O terminations. Electrically, they are compatible; however this would require a SIL review of the existing safety I/O before they could potentially be moved to a BPCS.  

About Siemens Moore APACS and QUADLOG

The Siemens Moore APACS and QUADLOG systems, initially introduced in 1992 will no longer have guaranteed vendor support as of Oct.1, 2020.  The APACS+ system combined the best of DCS and PLC functions into a combined platform. The system was built using the available standards providing the first open architecture for 3rd party extensions. Throughout the 90’s enhancements were added and the APACS+ system was recognized as a leading platform in the areas of Batch and Hybrid control, and integrated control with TUV safety certification. However, component obsolescence and advancing technology have overtaken this product family, and thus ensured its maturity. Hardware availability is declining, in particular the Processors and Communication Modules are increasingly difficult to find through 3rd party suppliers. Operating systems that support the engineering environment and specific server hardware are no longer offered or supported by Microsoft.

One particular advantage of implementing a migration effort with the APACS+ system has been the simplicity of the configuration and programming tools. This lends itself well to the conversion process when as building the logic. The 4 languages used in the 4-Mation software are directly relatable to most of the current systems including PLC ladder logic. It is not the intention of this document to detail the specific programing differences, however it is worth mentioning that the original intent of the APACS+ programmed logic is much easier to capture and document for the purposes of conversion.

APACS+ System Migration Considerations


Over the life span of the APACS+ system, there are various architectures that have been removed from production due to advancements and component availability. The initial system was released with the proprietary MBUS/MNET communications system based on the MAP protocol. This has been discontinued and most of the systems in operation today are now connected via Ethernet and the Industrial Ethernet module (IEM). This also means that the required backbone for communications, including fiber optic cables, may be re-purposed when the system is migrated. MS Windows XP (IEM OS) is the latest version that will support the MBI card required to connect to the APACS+ system and MS Windows 7 is the latest version that will support the engineering platform.  


At the time of this writing, there are currently no options available for a phased in approach to migrating the QUADLOG safety system. This would include “controller only” options. This is due to the additional system and I/O diagnostics inherent in the Quadlog safety system. There are however options available for retaining the I/O terminations and avoiding a complete re-wire.

I/O Density, Footprint and Channel Types

The APACS and Quadlog I/O modules are 16 and 32 channel cards. This channel density can potentially create and issue with the existing system footprint. Most of the current systems do not support the required channel density and will require additional module racks and I/O cards. Additionally, the APACS and QUADLOG I/O may be configured with a mix of Inputs and Outputs on the same I/O card. Some vendors have addressed this well with their approach to migration of mixed I/O types and density.


There are many factors to consider when choosing a migration path and the success of any system migration, regardless of the target system, will depend on the following;

  • Verification of the current system (Is it possible to use existing wiring?)
  • Is the plant documentation up to date?
  • User requirements planning – taking advantage of new technologies
  • Detailed migration strategy and planning
  • Functional Specifications and as-building of the current system - (orphaned or unused programing?)
  • Cut-over planning for hot and cold switchovers and phased transitions
  • Implementation and staging
  • Knowledgeable support for both original and target systems
  • Use of engineering software and conversion tools to save time and reduce errors
  • Training operators and verifying the configuration in a risk-free, offline environment

Finally, choosing a well-integrated system for both graphics and cpu will be the least expensive approach in the end. Managing a single system with vendor support of all hardware and software components reduces the risk of partial obsolescence and interfacing problems. Typically software upgrades are proven for each vendor as a complete system and not across a multiple vendor platform.

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