1734-FPD

[BJR 0]

What exactly are the functions of the FPD? I understand after so many cards you need more backplane power. But I understood that it is the point that you can bring in external power for the I/O. The way I have always designed things with the SLCs and MicroLogix is that since there is always a + power terminal going to each output card, that you run a 24V+ wire through a Master Relay or a Safety Relay contact depending on the safety risks of the machinery and then run that wire to the output card. This way no matter what the PLC does there is a hardwired power supply to each output card that is killed by the emergency stop. I thought that by using a POINT I/O system that this could be accomplished by putting all of my input cards first followed by a FDP module, followed by all of my output cards to the right. I was fooled into thinking this is working like a SLC card on the 1734-OB8E cards because e-stopping the supply wire to the FDP module caused the voltage to dissappear at any outputs that were still on in the PLC. But it is not really working on 1734-OV8E cards becuase these are negative logic and does not do what I was hoping on the 1734-OW4 relay cards I tried. My first question in general is how do you properly hardwire an "e-stoppable" supply wire used by the outputs to this type of system? I can tell you what loads I have tried on the OV8 card and the results I get when e-stopping but I want to dig up the data sheets on the devices if I can and share them tomorrow when I have more time. Looking for some good information on the FDP and proper e-stop hardwiring with these output cards to begin with. Thanks!

[rdrast 3]

The FPD module can be used to supply additional backplane power if needed, OR it can be used to switch the backplane power from one voltage to another. If you were combining 24 VDC modules, and 120VAC modules, you would need an FPD to isolate the two sections. Mainly, that's needed because there are so few terminals on the PointIO terminal blocks. The OV8E is a SINKING type module, so isolating the +24V will do nothing, as the logic will still drive the outputs ON which will sink them to power-supply common. I wouldn't know how to handle your ESTOP situation, in general, I'd suggest isolating the high side (unswitched) power to the field devices. Simply opening up the low side (switched, common) to me seems problimatical, simply because of how many possible ways there is of getting something shorted to common.