Published 24/03/26
Physical machinery guarding is easily visible and so it is quite obvious if a hazardous part is guarded, that the construction of the guards used is suitable for the application and that the risk is therefore appropriately mitigated. The safety of the control system however is less obvious.
Often the safety aspects of the control system on a machine are not fully understood, either by machinery designers or end users, leading to the potential for hazardous situations to occur. It is important that the reliability of the safety-related control function (SRCF) is known because, should it be inadequate, machine operators may, for example, inadvertently access hazardous areas through nominally interlocked guards. As machine automation becomes more complex, it is becoming more important to demonstrate the control system safety in a way that can be easily understood.
Designing safety-related control systems was once fairly straightforward when machinery used only electromechanical safety components in the control system but with the introduction of more complex components such as safety PLCs, a different approach is necessary. This approach is known as functional safety, and there are two standards which give a method of meeting the safety requirements: EN ISO 13849-1 and EN 62061.
Unfortunately for machinery designers, these standards are complicated and many organisations struggle to interpret them correctly. A key point, which we regularly see as having been overlooked, is that the required level of safety (Performance Level (PL) or Safety Integrity Level (SIL) depending upon the standard used) must be determined before the safety related control circuits can be designed. In fact, the new Machinery Regulation, which will be the main legislative instrument for Machinery from January 2027, explicitly states that these performance requirements are to be recorded as part of the design Risk Assessment for a machine.
But just designing the safety-related control functions is not sufficient. Once designed, the circuits should be verified to show that they meet the required performance based upon the machine duty cycle, control circuit architecture and components specified.
Finally, once the machine has been built and the safety circuit is functioning, the safety-related control function should be validated to ensure that it functions as expected and in accordance with the required safety level.
Of course, these requirements apply to new machinery but it is also important to apply the same principles to control systems of legacy machines when they are upgraded. If upgrading from safety relays to a safety PLC on a production line, for example, then the standard originally applicable for the safety system will likely not be adequate for the new circuit. Other upgraded components which will not be covered by the original standard include safety functions on motor drives such as safe torque off (STO) and Safe Stop 1 (SS1), coded magnet guard interlocks and safety bus systems.
At Conformance we work with safety-related control systems every day. We assist our clients with all stages of functional safety of machinery, for example, guiding you through the standards, helping with the risk assessment and subsequent identification of the required safety level for each safety function on the machine, guiding on the safety circuit design and verification of each safety function. We can also assist with creating validation plans to obtain evidence that the safety functions are reliable once installed.
Engaging Conformance early in the design process can not only help avoid costly redesigns and development delays, it also ensures a safe machine so that the risks of accidents are reduced and the resultant expense of downtime and legal action can be avoided. For support with functional safety or to speak to one of our machinery safety experts please contact us.