Paul Laidler, business director for machinery safety at TÜV SÜD Product Service, a global product testing and certification organisation.
Electromagnetic compatibility (EMC) is an issue that many machine builders find complex and confusing. However, machines offered for sale in the European Union are required to carry the CE marking to show compliance with the Machinery Directive. For any machine that includes electrical or electronic components in order to comply with the Machinery Directive it must also meet the EMC Directive (2004/108/EC).
There can be no doubt about the need for EMC. Who, for example, has not been listening to a radio that has experienced interference ‘chirps’ from a nearby mobile phone? When it comes to EMC and machinery, the situation could be much more serious. For example, if the control system of a machine experiences electromagnetic interference it may malfunction and create a dangerous situation. Conversely, if the electrical and electronic systems fitted to a machine generate a high level of interference, they may also cause other equipment nearby to malfunction.
It is to help guard against situations like these that the EMC Directive, 2004/108/EC was put in place. In the UK, this directive is implemented by the Electromagnetic Compatibility Regulations 2006.
Understanding EMC requirements
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 website – 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 reasonable level of immunity to electromagnetic disturbances. In addition, a fixed installation, which of course includes the majority of machines, must be installed by applying good engineering practices and respecting the intended use of its components.
But how can machine builders be sure that their products really do have satisfactory EMC performance? It is very tempting 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, it is reasonable to conclude that the whole machine must also meet them?
Unfortunately, that’s not how it works and it is relatively easy to see why. Consider, for example, a variable speed drive that produces a level of electromagnetic interference about half of that acceptable under the regulations. Clearly, there is no problem in stating that this drive complies with the regulations. However, if you put four of those drives on a machine, is it reasonable to assume that the machine complies with the regulations, simply because each of the drives is compliant? 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 problem can be neatly summed up with – ‘CE plus CE doesn’t equal CE’.
But how should machine builders demonstrate compliance with the EMC Directive? The directive specifies that they should compile technical documentation to show that basic requirements have been met and then complete a Declaration of Conformity. 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 verified is by testing. This opinion may be considered by some as rather controversial, but when the Health & Safety Executive 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 manufacturers to carry out or arrange for the carrying out of such testing and examination as may be necessary to ensure that the article is so designed and constructed that it will, as far as is reasonably practicable, be safe and without risks to health. In the context of EMC, in most applications it is the electromagnetic 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 electromagnetic disturbances, the HSW requires this to be carried out.”
This statement leaves no room for doubt about the necessity for EMC testing of machines in the vast majority of cases – there is simply no shortcut to achieving compliance with the EMC Regulations.
Unfortunately, there is also no doubt that EMC testing can be complex and time consuming, especially for the majority of machine builders that lack in-house expertise in this specialist area.
Few would deny that meeting the EMC requirements in relation to machines can be a daunting process, but ignoring those requirements is not an acceptable solution.
There is no shortcut to achieving compliance with the EMC Directive in order to meet legislative requirements and to ensure safety, machines must be thoroughly tested.
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