1734-EP24 vs 1734-FPD

Hi,

To section the field power (cut power to outputs but not inputs) - is it then necessary with the FPD, or does EP24DC also have this possibility?

It seems as the power supplied to EP24DC will feed both system and field so if i cut one of them, then the entire IO-node will be faulted.

Also, if I now replace then the EP24 could they still be needed given the amount of IO cards?

I'm afraid there will be some costs over budget here...

BR
Jon

Use the FPD to isolate output power. The EP24DC will cut all power from the "previous" modules to the left and supply new to the right. You don't want to use the EP24DC to follow, say, a safety relay; it will drop module communication power to the following modules and will result in a rack fault.

FPD supplies field power only. So, if your rack looks like this:

AENT-IB4-IB4-OB4-OB4-FPD-IB4-IB4-OB4-OB4

Then the first two output cards will be supplied from the 24VDC on the AENT, and the second two output cards will be supplied from the 24VDC on the FPD. Likewise, the input common for the first two input cards will be the input common connected to the AENT, and the input common for the second two input cards will be the input common connected to the FPD.

The EP24DC, on the other hand, supplies field power and backplane power. So, as well as the above, the EP24DC supplies the 5V power to cards to the right to make them power up and do their thing.

The reason you use an FPD is because you need to isolate the I/O field power in sections. The reason you use an EP24DC is that the AENT can only power up so many cards - any more than that, and you have to use EP24DC's to power the rest. The EP24DC does allow you to split up the field I/O power as well, but it's a secondary function.

Check the maximum bus power available on your AENT (note that the AENTR can supply more bus power than the AENT; this has gotten me out of trouble in the past). Then check the bus power requirements for each of your I/O modules and work out where you hit your limit. That's where you'll need an EP24DC.

My general rule of thumb based on a rack of mostly digital I/O is that I can get about 8-10 cards onto an AENTR before I need an EP24DC. But as I say, that's just a rule of thumb, and you'll have to do the math to work it out for sure.

It's worth noting that as cutting power to an FPD only cuts field power, the module still communicates and everything is happy. Whereas cutting power to an EP24DC turns the cards to the right off completely, meaning your AENT can no longer see them, and yes, you will have an I/O fault

Thanks both.

I will try out the tool IAB from the AB web page to dimension the nodes w respect to power and get the FPD.

AB also informed me of potential data cap limit when using many analog cards. Also, they discouraged from "too long/much" use of the AENTR because "the first node will take all the traffic".