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Good design practices derived from industry standards dictate that control systems must keep process control functions separate and operationally independent from safety functions.

By John Boville, Hybrid Industry Marketing Manager, Process Automation Innovation and Marketing, Schneider Electric.

Automation systems control physical assets that transform energy and raw materials into finished products, and all being well, the finished product is sold at profit (which in simple terms is the difference between that product’s selling price and the cost of the energy and raw materials used to make it). It is also important to keep in mind production assets are significant capital investments.

If you’re in business, you’ll know all about maximising your Return On Capital Employed (ROCE). For production assets, this generally means making as much product as possible while keeping the plant running reliably and safely. To maximise asset productivity while optimising (not necessarily reducing to a minimum) energy and raw material costs requires access to data from multiple points in the plant’s various systems. This data can then be analysed and used to make adjustments to processes in real time.

As we know, the performance of new electronic components continues to advance at a rate which generally follows the principles of Moore’s Law. Modern automation systems which take advantage of these latest levels of performance can affect ROCE by speeding up the process or by reducing the time to design, build or install and commission production systems.

So, what does all of this have to do with Common Safety controllers? Let’s consider how they can help an industrial enterprise improve profitability by improving operational safety, reliability, efficiency and ultimately profitability.

Programmable Safety: Technological Advances

Recent advances in electronics and network design have made it possible for industry to take advantage of transparent, secure Ethernet communications to drive increased process visibility and improve the operational profitability of their plants safely. These same advances also make it possible to design common safety controllers that integrate control and safety features in a single system. Industrial enterprises can now reap the benefits of world class automation system performance as they design, build and operate their plant control and safety systems. This allows them to measurably improve profitable reliability and efficiency, safely.

What Exactly Is Common Safety?

Good design practices derived from industry standards dictate that control systems must keep process control functions separate and operationally independent from safety functions. This is intended to ensure the process control system has no ability to compromise the safety system in the event of a failure and vice versa. Traditionally hybrid industry control system designs have accomplished this using a programmable logic controller (PLC/PAC) to control non-safety-related plant functions, combined with a physically separate (often hard wired) system to control safety functions.

Today hardware design approaches exist that allow the required degree of separation mentioned in the standards to be obtained by design within a single module.

Let’s find out more about what common safety is and how it works:

  • Common Safety is a technology that allows a closer integration of process and safety functions. It ensures that both process and safety operations are separate and independent with different hardware resources in a common engineering environment.
  • Safety and non-safety modules are integrated seamlessly to provide a high level of flexibility, adaptability and easy-of-use.
  • The common engineering environment provides independent tasks for the safety functions

Common safety controllers such as Schneider Electric’s Modicon M580 Safety PLC can provide the following benefits to hybrid industry users:

  • Closer integration with plant control automation systems
  • Ease of use
  • Performance, flexibility & interoperability with plant networks and systems
  • Reduced engineering time and cost needed to design and implement new safety systems
  • Less time needed to get new systems up-and-running
  • Simplified architecture which improves ease of maintenance

In the case of the M580 Safety controller, the architecture consists of two distinct microprocessor systems. One system is dedicated to safety functions, the other dedicated to control functions. Each microprocessor has its own dedicated memory to store operating programs, data etc. Data exchange between the safety and control systems takes place using a dedicated memory area. The goal of this design is to avoid a malfunction in the control processor negatively impacting the safety processor and vice versa. The required degree of separation is achieved in a single programmable control package and the common safety controller can share the same programming tools and I/O structure as other systems in the plant. In the right application this approach can reduce cost and improve profitability.

To read more detail on balancing the equation between asset productivity, safety and profitability in industrial enterprises, see the white paper entitled: How to increase profitability by improving operational reliability and efficiency, using common safety.

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