Hi Brian and the group. This is a bit of an old chestnut, with as many answers and reasons as you'd care to make. It's just not possible to state a case which covers all situations..
At the one end of the spectrum you have RF equipment emitting all over the place, just under limit, and when you put these together you have additions and subtractions which can entirely change the emissions envelope. At the other end you have essentially low frequency equipment which can have it's emissions very easily predicted with a high degree of certainty. The EC last year allowed for 'systems' to be assembled with CE marked sub systems, and claim compliance. This was a common sense approach to situations in the automation and machine tool and laboratory type industries where, for instance, you have an Inverter motor speed controller which is CE marked in a panel, and another, and another, and another... etc. It doesn't take a brain surgeon to realize that a multitude of inverters = a lot of emissions, and that to make these compliant with 50081 (for instance) would take a great deal of expense and hardware, if indeed it was possible at all. It is not the intention of the Euro EMC directive to make things impossible to market, but to ensure that no-one catches a steal on marketing advantage by taking EMC shortcuts. We had a situation where any machine which had more than a few inverter speed controls was uncompliable(?). The 'Systems' approach gave enough versatility to the regs to enable such equipment to be manufactured and supplied with evidence of 'Due Diligence' being applied. Essentially. this really means that 10 seperate inverters in their own cabinets (all of which have a CE mark) are not really any different to those same 10 inverters placed into one cabinet. Another view might be that of equipment comprising many 19" rack mounted CE marked instruments connected together with cables as an ad hoc 'system'. If these instruments are standing on tables and benches, as would be in a laboratory type situation, should they be subject to different rules than if those same instruments and cables are stacked on top of each other, and yet again if that stack of instruments is housed in a 19" rack. That's my twopence worth, look forward to hearing the views of others. Chris Dupres Surrey, UK. --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
