Modular approach to safety systems
30 March 2017
When using modular safety systems it is essential to ensure that key features are considered in order to maximise the benefits, says Kevan Cowley of Wieland Electric
When designing safety systems for complex machines, the first step is clearly to carry out a risk assessment to identify which safety features are required. The next logical step is to investigate which technologies can facilitate straightforward and cost-effective compliance.
To that end, there has been growing recognition in the last few years of the benefits of modular, configurable safety controls. Not least of these benefits is the ability of a modular system to reduce the complexity of the wiring, compared to using stand-alone safety relays. This is because stand-alone safety relays need to interact with each other, which can require very complex wiring, so that design time, installation and commissioning are often extended.
Therefore, taking a design approach that reduces complexity can significantly reduce the overall life-cycle costs of a machine safety system – as long as there is no compromise on safety of course.
Modular, configurable safety control systems provide a very clear illustration. These use centralised input/output (I/O) systems that reduce the hard wiring requirement and therefore the overall complexity. However, the complexity of the wiring can vary considerably between different types of modular safety systems.
Which modular system?
There are two types of modular solution currently available – mechanically configurable systems and software-based safety circuits. Mechanically configurable options tend to have more complex wiring, so a software system that uses a centralised I/O will be the preferred option in the majority of situations.
However, there is also variation in the level of complexity between different types of software-based systems, particularly in terms of the complexity of the wiring requirements for monitoring of faults.
With some systems there is also a limitation imposed by having a fixed number of I/Os, so it may then be necessary to pay more for a system when expandable I/O can be beneficial. This can be a particular problem for smaller systems as it may be necessary to bear the cost of many more I/Os than are required upfront, often making the use of a modular system financially beneficial.
In contrast, some solutions offer the controller separately from the I/O module, which makes it very easy to match the I/O requirement precisely to the requirements of the system.
Another issue can be the need for communication with a wider network. If stand-alone relays are being used then feedback will require additional contacts. When using the software version, you can consider whether it can offer a common protocol. Also, can the controller send diagnostic information through these gateways?
There are also significant benefits if any full reports are automatically date and time stamped as this will make it easier to identify the root cause of the fault, and ensure simple comprehensive compliance documentation for your safety system.
When using a software-based system it is essential to include a self-validating verification process, as this will prevent mistakes being made and ensure compliance with appropriate regulations. These can also be date and time stamp verified. Without this functionality a considerable amount of time is required for producing the written reports, diagrams and photographs necessary for system verification.
Another thing to consider with a software-based modular safety system is the cost of the software itself. It is quite common practice to charge a licence fee for use of the software but in some cases this will only cover basic functionality. An extra charge will be required for any extra functions, such as burner control and press functions.
At the other end of the spectrum, companies such as our own make the software freely downloadable with all of the functionality included as standard.
When considering modular safety systems then, it is important to address all of the criteria that have been discussed here to ensure all of the potential financial and performance benefits are achieved. Taking time to research the various solutions available at the beginning of the project will pay dividends in the longer term.