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Is machine wireless safety truly safe?

Is machine wireless safety truly safe?

Neil Dyson of TUV SUD Product Service looks at wireless safety in the context of safety related control systems, and details exactly what machine builders need to know when they are looking to install wireless safety technologies.

Safety related control systems (SRCS) prevent a hazardous condition from occurring. As its complexity will vary depending on the type of machine into which it is installed, and SRCS can be a separate dedicated system or be integrated with the normal machine control system. 

Control systems for machinery, can be electrical, hydraulic, pneumatic, or a combination, and are often required to perform safety-related functions. Examples of SRCS include interlock switches for guards and emergency stops.

The Health and Safety Executive (HSE) defines safety related systems as: “A control system or device is deemed to be safety related if it provides functions which significantly reduce the risk of a hazard, and in combination with other risk reduction measures, reduces the overall risk to a tolerable level, or if it is required to function to maintain or achieve a safe state for the equipment under control.”

Of course, wireless connectivity of both machines and their SRCS are becoming increasingly popular. For example, wireless safety foot controls are now available on the market and offer distinct advantages as they are flexible to position and easy to mount – wherever the operator can monitor the process most easily. However, the rapid pace of technology development has created a situation where machinery manufacturers and end-users are often unfamiliar with the regulatory requirements and how they should be designed and deployed.

Machine builders and end-users should therefore ensure that wireless systems are installed as per the manufacturer’s specific mounting and wiring instructions. For example, to install equipment the wireless switch should be mounted on an even surface, and the radio switch must be installed by strictly following the mounting and wiring instructions for the receiver.

While wireless technology affords a great deal of flexibility in terms of how equipment can be deployed across a site, it does have limitations, which is a concern for safety systems where 100% reliability is required. One such limitation is the sensing range between receiver and transmitter, the strength of which will depend on the local conditions. The radio signal can be strongly affected by conductive materials, as well as other sources of radio interference, and can sometimes lead to a dead spot for wireless connectivity. This can be caused by metal parts, such as wall armour, insulation and metal foils, which are known to reduce the penetration of radio waves to 0-10%.

Wireless safety reliability 

In the European Union (EU) it is mandatory that radio equipment meets the ‘essential requirements’ of the new European Union Radio Equipment Directive (RED) 2014/53/EU, which replaced the Radio and Telecommunications Terminal Equipment Directive (R&TTE) on 13th June 2016. While the RED will become the required method to show compliance of radio and telecoms equipment sold across the Europe Union, equipment compliant with the current R&TTE Directive may continue to be placed on the market until 13th June 2017. 

Products which fit within the following definition are subject to the RED: “Radio equipment – an electrical or electronic product which intentionally emits and/or receives radio waves for the purpose of radio communication and/or radiodetermination, or an electrical or electronic product which must be completed with an accessory (such as an antenna) so as to intentionally emit and/or receive radio waves for the purpose of radio communication and/or radiodetermination.”

In order to reduce both costs and time to market for new equipment, we expect that many machinery manufacturers will rely on the use of wireless modules that already meet some or all of the RED’s essential requirements. However, once these modules are integrated into another product, the regulatory requirements will change as the host machine falls within the scope of the RED. Under the RED, the manufacturer must also take account reasonably foreseeable conditions, ie use of the product outside of its intended use. 

The most common method of demonstrating compliance with the RED essential requirements would be by using ‘Harmonised Standards’. These are written and published under an EU mandate, and provide a ‘presumption of conformity’ (or compliance), provided they are applied in full.  

As the scope (and the safety and radio essential requirements) of the RED differ from the R&TTE, additional standards are required and existing standards must be amended. While harmonised standards are being reviewed for publication under the RED, the European Telecommunications Standards Institute (ETSI) stated that it would not be possible to complete all of the required standards by 13th June 2016. Likewise, some standards produced by CEN/CENELEC still require amendment. 

While the machinery world becomes progressively wireless, the regulatory world is playing catch-up. In the absence of ETSI RED standards published, it is mandatory for any manufacturers wishing for an early implementation of the RED to apply to a Notified Body for a Type Examination Certificate or a Full Quality Assurance Approval. 

As the machinery world goes wireless, it is vital that  safety functions can still prevent the initiation of a hazard or detect the onset of a hazard, as they would when they would previously has been wired. While wireless safety related control systems grow in popularity, given the benefits of faster response times and a more flexible installed base, they must still be capable of taking the necessary actions to terminate a hazardous event and achieve a safe state to keep operators from harm.

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