Thursday, 23 October 2014

Andy Preston, UK Drives Product Manager, ABB writes: Our modern world is obsessed with health and safety, so much so that it is often taken too far. We’ve all heard the stories – school children banned from eating triangular flapjacks because they are too pointy and dangerous, Frisbee catching for dogs banned for health and safety. The list goes on, so much so that the Health and Safety Executive (HSE) publishes a myth busting page to explain the real reason behind these sorts of stories.

As a process or maintenance engineer, you of course take health and safety seriously, but is it too dominant in your working life? A typical application or process will have its motors, drives and controls - it then might need an entirely separate safety system to ensure that the process can be stopped safely or fails in a safe manner that won’t injure people or put them at risk.

It all adds to the time and expense, as well as increasing complexity. Surely there is a better way of building safety systems?

Take the variable-speed drive. What are surely needed are drives that take the safety functions on board, removing the need for external components. One of the major safety functions is safe torque off (STO), which temporarily cuts the voltage to the motor without the need to shut down the whole drive, guaranteeing no motor torque. Safe cleaning and maintenance of processing machinery can then be carried out, while the drive remains ready to resume normal operations.

Having this on board could help engineers interface machinery directive compliant emergency stop functions, with no more need for contactors or safety relays.  The result would be solutions that are safer and more cost effective.

Of course there are many other safety functions that are useful but not always required in every application. Functions certified under the Machinery Directive include SS1 (Safe Stop 1), which ramps the controlled motor down to zero speed; SSE (Safe Stop Emergency), emergency stop ramped; SBC (Safe Brake Control), used for proper safe management of a crane brake; SMS (Safe Max Speed), typically used on centrifuges to prevent damage; and SLS (Safe Limited Speed), which ensures safe limited speeds for operations like jogging and threading.

It would be good to have these in a built-in module. This would make it easier to build compliant safety systems the way you want them, as it would remove the need for complex and expensive programmable safety relays. Parameter driven programming would also be beneficial – as would doing away with the need for feedback devices such as encoders.

You’ll be pleased to know that such a drive already exists. It’s the ABB industrial drive, ACS880 and it offers all these facilities and more. To discover more about how the ACS880 can help build efficient effective safety into your process, go to www.abb.co.uk/energy


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