Is it a machine or a system?

Just a few thoughts...

"The Machinery sector is an important part of the Engineering Industry. Machinery consists of an assembly of components, at least one of which moves, joined together for a specific application. The drive system of machinery is powered by energy other than human or animal effort."


This seems to be an fairly extensible definition...


The HSE's interpretation of the Machinery Directive is here


In a busy non-partitioned working environment with lots of moving open conveyors etc it is common to have a network of zonally grouped emergency stops covering moving equipment across readily definable and inuiitively understood visual fields.  This not only reduces confusion over what EM stop button to press in any given emergency, but also reduces the local background noise allowing people to concentrate and communicate more easily to respond to what has happened.


Having quickly looked I can't find mention of this type of arrangement in the Machinery Directive. 


Based on this example alone, I expect you will need to make some global and zonal level risk assessments and safety related system integration design choices that are not fully explored in the Machinery Directive.


James

There are several aspects to consider:


1) If the control systems of the various parts are connected you should consider it as a machine. The interconnection wiring will need to follow machinery standards rather than building wiring standards.

2) The standards for electrical parts of machinery such as EN60204 do not differ much from European wiring standards (the UK deviates the most with ring final circuits and underrated breakers in consumer units).

3) With all large interconnected systems the risk assessment is key. This will allow you to determine the hazards from the electrical supply and various isolation regimes.

Have you been quoted specific differences between  BS 7671 and EN 60204?


Best regards


Roger

Hi Roger


Thanks for the response.


We have had numerous debates interanlly but my view is very much (reading what the Machinery Directive is defined as) that it is numerous 'machines' making up a whole and therefore  the machinery directive is the starting point, which then cascades down to the Low voltage standards for example.

The confusion has arisen as the 'machine' which is a number of conveyor systems connected is designed under a standard produced within our group in mainland europe, but people within the UK offices are questioning if the design meets the requirements of the UK. Whereby some believe it shoudl be designed as a distributed system not a maachine.

Does it have a centralised control system? If so it would appear to be a number of subsystems making up a machine.

Are any specific UK requirements being questioned? One of the usual ones is the use of SY cables instead of SWA.


Best regards


Roger

Paul,


The scope of the question you have raised is quite wide, and I may have misunderstood what you mean by "distributed system".


This a summary of my approach and understanding... 


Being from a control and automation background I would tend to always use the term distributed control system (DCS). This will normally be a highly complex networked and distributed computer control and automation system that could be running in continuous or batch mode or both. Even if the wider system has multiple parallel production streams, each with an identical distributed control system, there will still normally be just one upper level supervisory [database] system interfacing with an internet based ordering system or other higher level business management tasking and production scheduling system. In the final analysis there is one big distributed control system. The term SCADA (Supervisory Control and Data Acquisition) is often used for smaller systems in this class. 


These are generally very complex control systems, classed as safety related systems at best. As such they cannot be directly relied on to guarantee operator or maintenance staff safety. If a crane moving in a crane isle is fitted with a sensor to detect obstacles, including a person in its path, then this safety system should operate completely independent of the main distributed control system, including its failure modes. There is no need to distribute the safety function because the crane motor, braking system and obstacle detection system are located in the same device. 


The safety systems (including hardware interlocks emergency stop isolation etc) are simple systems that provide the physical constraints to what the DCS can do. They are normally defined independently of the DCS, so that difficult to resolve questions in regard to operating context don't apply. [Context is more relevant to active safety systems required for aircraft fly by wire systems (keep going best endeavor until you land), rather than passive fail-safe systems that generally apply in manufacturing facilities or automated warehouses.]


Similar ideas can apply to layered cyber security protections as well. For example, if there are hardware settings which if altered maliciously or otherwise could lead to the damage of hardware and thus significant cost and downtime, then I think consideration should be made to fully partitioning these hardware limits/constraints to make them independent of changes/bugs/failures to the DCS control space.


James

Thank James


​Also being from a controls background I can see why my question is a bit 'open'.  It is much more to do with the elecrical design rather than the safety, and whether you design electrics to machinery directive and include other 'best practices'.  As an eample that Roger picked up on, the cable from the motor isolator to the motor, as it is not SWA or SY cable, should it be encolsed in copex for protection as an example? From our UK perspective we belive it should, from the interpretation of the Machinery Directive of others, the fact it sits within the confines of the machine (underneath the conveyor) it is in theory protected within the confines of the machine.


​To be honest I do not believe there to be a definitive answer, as long as you follow the directives and use the required standards and can show from the Technical File for CE marking you have done this it still comes down to interpretation in the end.

Paul Roman,

What you are describing is a system or assembly of linked machines under the machinery directive.

BS7671 is irrelevant.

The assembly will require CE marking as a whole under the MD.

Electricaly you would be looking at EN60204-1.