1756-OD16D for electronic fusing...

Has anyone ever thought of doing something like this?

1756-OB16D output cards used as control power distribution and electronic fusing.

Each output would go to a generic control station to supply power for say an 8-port M12 Micro DC connector block which could have proximity switches, jog buttons, and possibly LED indicators plugged in. These devices would then be wired to 1756-IB16 input points.

Perhaps eight devices per output point on the OBD card...or however many a point can support.

I am thinking of future NFPA70E compliance and switching our devices to DC, and at the same time, address the frequent fuse blowing and short-to-gnd chasing downtime "while I'm at-it..." We contend with a nasty wash down environment that requires fused outputs and they cost us considerable downtime to fault find and replace fuses which are in a dry area up two flights of stairs.

Why is this a bad idea? Something tells me there is a programmatic or electrical reason this would not work well...

I need to look up the specs of the card...but my 300 baud acoustic to GSM redneck portal to the www at half the speed of smell won't support streaming pdfs.

Wouldn't it be better to monitor the fuse status as an input to the PLC?

Sounds like it could work, but you don't necessarily need the D version, I'd think the 1756-OB16E would be a better choice.

I actually use these for exactly that purpose though:
Siemens 24VDC Diagnostic Extension

They work great, and have a contact status you can use as an input to a PLC. Yes, they require physically resetting each faulted channel, but I prefer to have someone go look. I do allow electronic resets on the 1756-OB16Es we use, but only two per module without requiring a physical reset as well.

Paul

We use these m12 blocks http://www.balluff.com/NR/rdonlyres...-5C72E8400E44/0/EtherNetBlocks_WEB.pdf#page=6 that have short and other diagnostics built in per port. Plus they are ethernet if you can use that and not have to do the p2p hardwiring.

Yes, the E, not the D.

Right now, all of our I/O and even drive control voltages are 120VAC. All our control fusing is remote from the production floor. Our controls are fused in small groups, so there several dozen fuses per production floor, and some panels have all fused outputs....Bottom line, lotsa 120v fuses.

~$400 for four or eight fused circuits, PLUS the fact that I don't have to stock and purchases fuses, PLUS the fact that I don't have to find the prints, climb the stairs, find the fuse, walk to the parts room, find the fuse, install the fuse...spend another 30 minutes fixing the cause of the 2nd blown fuse...meanwhile the PLC guy has to force a bunch of stuff to get production rolling...this can amount to a few minutes or over an hour of major downtime.

If the PLC supplied the power and fusing, it could automatically prompt the user. If I keep my wiring between modules and DC Connector blocks consistent, replacing one could be pretty painless and fast.

The ethernet modules sound cool, but I don't want another LAN and our PLC ethernet subnet doesn't have enough space to support the two dozen or so blocks we'd need to add...I think we have about 200 nodes right now.

I figure $400 for 4 or eight fused control circuits, and let the progammer decide when and how to log, reset, and react to fuse faults. It might be slightly more expensive at the start, but would continue to create returns in the form of fuse inventory and uptime.

I am about talked into this. Thanks for the feedback, I will follow those links when I get free at work later.

Paul

OkiePC said:

I will follow those links when I get free at work later.

Paul

Click to expand...

Paul you get free time at work? Do you need any help?

This looks like a great idea I think I will be looking into this. All current systems that i build have 2 panels the control panel ( less thab 50V) and the power panel (50V and up)

I have not yet had the chance to pursue the details of the 1756-OB16DE.

I have followed the links above provided by PLC Kid and rdrast, and they both look like good ideas.

The problem with the Ethernet I/P blocks is that they aren't high pressure washdown rated, and probably would not do well with the sanitation chemicals we use.

Hopefully, tomorrow evening I will get more time to study this. For now, I have to figure out what is wrong with a pressure transmitter analog card before I get outa here at 11...

1 amp per point. 8 amps per card, so a power budget of 500mA per point to drive each branch.

1.8 amp "trip point"

Am I correct to assum that is where the electronic fuse trips?

The module will trip at 1.8 amps after a very short time, or 4.1 amps within a few milliseconds. The 'fuse reset' resets all tripped outputs at once. I cannot recall if a single trip only affects one output or multiple ones.

I see the Siemens module I linked has been upgraded to allow remote resetting, nice feature. It also allows for sequential powering up of each output, I'd look hard at that honestly.

In any event, aside from the structure I use, this is the logic I use to monitor the 1756-OB16E modules, and allow for a reset:


The MSG is just a CIP generic "Reset Electronic Fuse"

Never used one of these, but may be something to look at...http://www.wago.us/products/28366.htm