Martin You didn't describe your product very clearly. A PLC can be many different things - It can be modular with power supply components, Logic and I/O modules or it could be a brick style with everything integrated under one housing. Typically there are provisions for 120/230 VAC power and I/O but I have worked with bricks that have only 24VDC power and I/O.
Another issue is what are you to analyze A narrow interpretation says no components and nothing below 50VAC or 75 VDC for the LVD. Unfortunately there is need for interpretation. I understand that there is a CENELEC document on interpretation for the LVD on these matters in the works. Any one know the expected release date? Components can mean many things. A resistor or capacitor is a component that must be considered in the design context - No LVD CE mark requirements. While a PC monitor is a component of a PC system but has an "intrinsic" or "direct" function and is marketed and packaged separately to the end user - LVD CE mark required here. What is not clear to me is how you would treat components within a PLC. A power supply module driven from 120 VAC would clearly need the LVD for CE mark. The analog Input module is a trickier problem. I believe you would need to coordinate isolation barriers with the PLC system but it is not clear if you must CE mark this module relative to the LVD. I have a similar problem with a communication card in a PC. The card is well below 50VAC or 75VDC so it appears that it doesn't need a CE mark for the LVD. It does for EMC and I believe the expectations are that I have the card meet the same safety requirements of the PC "IEC 950". You mentioned analysis of "circuits" relative to the LVD. This is an awkward perspective. Perhaps I don't understand your wording but you are implying that you could pay attention the hazardous circuits and ignore the rest. You obviously need to analyze the isolation barriers between the hazardous and SELV circuits and in that perspective the whole product with both the hazardous and SELV circuits falls under the LVD. All that said - I think your real problem is that your customer wants more than the CE mark, they think they want the PLC to meet the needs of the PLC family standard. If you do not comply today - this could be a tall order. If it is just CE then I think you could make a case for meeting the EMC and safety portions of the family standard only. The difficulty is in separating those requirements from the operational requirements, like programming conventions that you talked about. Hope this helps And of course these are only my opinions and not that of my employer Regards Chris Wells Sr Des. Eng. Cutler-Hammer well...@ch.etn.com ------------- Original Text From: C=US/A=INTERNET/DDA=ID/martin(a)pc.mei.melco.co.jp, on 6/11/97 9:14 AM: Sorry about the previous attempt!! I hit the send button by accident! ********************************************************************* Dear All, hopefully one of you out there can help me with this, My company has recently been contacted by an organisation stating that our product (programmable logic controller) should comply with the requirements of EN61131-2 (the standard for programmable logic controllers) as it is listed on the OJ for the Low Voltage Directive. No problem with that, we already comply with the safety aspects of this standard. However, they also think that we should test to and satisfy the functional requirements as well as the safety requirements. To my knowledge LVD is concerned with the safety of circuits operating at voltages above 50VAC or 75VDC. The directive states that the safety requirements only need to be met and most of the standards listed on the OJ for this directive are applicable to the safety requirements portions only. Also at the beginning of EN61131-2 it states that this standard takes precedence over all other standards EXCEPT basic safety standards. EN61131-2 isn't actually a safety standard as such, it covers design and definition of PLC systems as well as design requirements for circuits operating within the voltage ranges that fall within the scope of the directive (and a whole bunch of other stuff I don't want to go into!). However, as many of the circuits within a PLC system are SELV they don't fall within the scope of the directive. Is there any justification for this organisation to demand this? Am I missing something here? Best regards Martin Ginty Mitsubishi Nagoya Works FA systems department
