Stephen Mitschke
August 12th, 2003, 11:38 AM
I do not know of anyone off the top of my head. Power Conditioners areavailable from Relcom Inc. (www.relcominc.com), Smar (www.smar.com), MTL,Interlink BT, and I think Wiedmueller is just starting as well. The bestway to find out, is to post to the FUN mail list and see what we get back.The reason to install a power supply in the field is so that you can have aredundant power supply so that if for some reason your home run cable getssevered between the field and control room, you will still be able to moveforward or gracefully shutdown knowing that the field devices are continuingto operate.Let me know if you would like to post your question to FUN.Ian-----Original Message-----From: Vachharajani, KalpenHi Ian,Do you know who makes fieldbus power conditioner - 24 VDC for use in Class1, Div 2 areas, UL or FM approved?Normal standard is installing bus power supply in safe area and then usebarrier before bus enters hazardous area. Do you know why would one wantto install power supply in class 1 div 2 area?Kalpen- - - - -In my mind it is cumbersome to first use a regular power supply impedance("conditioner") and then put a barrier after it. I prefer to use an isolatedbarrier with built in power supply impedance. The barrier should preferablyalso have a repeater built into it. This allows you to make a larger networkconsisting of a safe area segment connecting several repeating barriers eachwith one hazardous area segment. This way you can connect many IS devices tothe same interface port. Non repeating barriers usually can only beconnected to the impedance and interface one-on-one limiting the number ofdevices per interface port raising the cost.The traditional entity concept considers the cable capacitance andinductance as a "lump" that has to be taken into the entity calculation.This limits the cable length to a few hundred meters at best. If distancesare longer you are forced to put the barriers in the hazardous area in someform of approved enclosure. Enter FISCO (Fieldbus Intrinsically SafeCOncept) as an alternative to entity. Among many differences FISCO providesmore power and also considers cable capacitance and inductance distributed.The C and L therefore need not be included in the calculation as long as itfalls within some specified (pretty wide) limits. Using FISCO you can simplygo ahead and run 1000 m of wire which usually is sufficient to avoid havingto place the power in the hazardous area. Both barrier and devices must beFISCO approved.Jonas- - - - To All:Relcom are developing field mounted power conditioner equipment that can beinstalled in Class I Div 2 Hazarous Areas in general purpose enclosures and using ordinary (non-explosion proof ) wiringmethods. What is even more exciting is that on the "safe side" ( FF deviceside ), a connectorcan be installed at the conditioner or the field device that can bedisconnected even when the field device is energized. This will certainlymake maintenance of FF devices a lot easier. I suggest that we all encourageRelcom to finalize this "Non-Incendive" solution for FF installations inHazardous Areas. In most of our plants, almost all of the plant is Div 2areas and there are very few and small areas that are Div 1 where thisproduct can not be used.Regards,Charles