Feature Machine Safety Don’t make EMC assumptions
There are several misconceptions around electromagnetic compatibility (EMC) of machines. Here, Paul Laidler, business director for machinery safety at TÜV SÜD Product Service, offers some advice on how to ensure EMC on an entire machine is achieved
espite the fact that electromag- netic compatibility (EMC) can be a complex subject when it comes to machine safety, it doesn’t alter the fact that there is an undoubtable need for it. For example, electromagnetic interference on the control system of a machine can result in the malfunction of that machine, in turn creating a dangerous situation. Conversely, if the electrical and elec- tronic systems fitted to a machine gen- erate a high level of interference, they may also cause other equipment nearby to malfunction.
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If each individual electrical or elec- tronic component in a machine car- ries the CE marking to the EMC Directive, then there is an assumption that the entire machine will also meet EMC requirements. However, herein lies the danger, as this is not necessar- ily the case.
Legalities
Machine builders have a legal obliga- tion to ensure that products offered for sale in the European Economic Area (EEA) carry CE marking. The CE mark- ing demonstrates compliance with applicable New Approach Directives such as the Machinery Directive and in order to comply with this particular directive, it is also necessary to show that the machine meets the require- ments of all other applicable directives. For any machine that has electrical or electronic components, that includes the EMC Directive (2004/108/EC). In the UK, this directive is implemented by the Electromagnetic Compatibility Regulations 2006. To understand the implications of these regulations, a good starting point is to look at the ‘Guide to the Electromagnetic Compatibility (EMC) Regulations 2006’, which can be viewed on the Department for Business Innovation and Skills web- site -
www.bis.gov.uk. Section Two of this guide includes statements that can be summarised as saying that equipment must be designed and manufactured so that the electromagnetic disturbance it creates is not excessive, and that it has a rea- sonable level of immunity to electro- magnetic disturbances. In addition, a fixed installation, which includes the
majority of machines, must be installed by applying good engineer- ing practices and respecting the intended use of its components. However, how can you be sure that your machinery really does have satis- factory EMC performance? It is tempt- ing to think that the answer is to use only components that are themselves compliant with the EMC Regulations. Surely, if all of the components used in a machine satisfy the regulations, is it reasonable to conclude that the whole machine must also meet them?
Above: Paul Laidler, TÜV SÜD Product Service
Nowhere in the EMC Directive does it state that testing is mandatory, but since there is no proven way of calculating or modelling the EMC performance of a machine, the only way compliance can be effectively verified is by testing. This opinion may be considered by some as rather controversial, but when the Health & Safety Executive (HSE) was asked to comment on this issue, it provided the following statement, ‘Section Six of the Health & Safety at Work Act (HSW) places a duty on man- ufacturers to carry out or arrange for the carrying out of such testing and exami- nation as may be necessary to ensure that the article is so designed and con- structed that it will, as far as is reason- ably practicable, be safe and without risks to health. In the context of EMC, in most applications it is the electromag- netic immunity of equipment that is of interest in relation to Section 6 of the HSW. If it is reasonably practicable to carry out testing for immunity to elec- tromagnetic disturbances, the HSW requires this to be carried out.’
Summary
This statement leaves no room for doubt about the necessity for EMC testing of machines in the vast major- ity of cases. Unfortunately, there is also no doubt that EMC testing can be complex and time consuming, espe- cially for the majority of machine builders that lack in-house expertise in this specialist area.
It’s not that simple Unfortunately, that’s not how it works. For example, consider a variable speed drive that produces a level of electro- magnetic interference about half of that acceptable under the regulations. Clearly, there is no problem in stat- ing that this drive complies with the regulations. However, if you put four of those drives on a machine, is it rea- sonable to assume that the machine complies with the regulations, simply because each of the drives is compli- ant? The machine may be compliant, especially if measures to control EMC have been incorporated in its design, but the point is that it cannot be assumed to be compliant. This prob- lem can be neatly summed up as ‘CE + CE doesn’t = CE’. However, this still doesn’t answer the question of how machine builders should demonstrate compliance with the EMC Directive? The directive spec- ifies that they should compile techni- cal documentation to show that basic requirements have been met and then complete a Declaration of Conformity.
Electrical Engineering JULY/AUGUST 2013
Above and below: machine builders that assume that all that they have to do to meet the
requirements of the EMC Directive is to use components that carry CE marking are following a
dangerous route
Therefore, those machine builders that assume that all that they have to do to meet the requirements of the EMC Directive is to use components that carry CE marking are following a dangerous route. As there is no short- cut to achieving compliance with the EMC Directive in order to meet legisla- tive requirements and ensure safety, machines must be thoroughly tested.
TÜV SÜD Product Service
www.tuv-sud.co.uk T: 01489 558 100
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