Inter posing relay
Inter posing relay
(OP)
Hi,
With regards to a Siemens DO card which has outputs rated 0.5A@24VDC if we are using these output channels to power 24VDC solenoid valves (0.3W &7w)would these require interposing relays as they are within the limits of the channel?
Thanks
With regards to a Siemens DO card which has outputs rated 0.5A@24VDC if we are using these output channels to power 24VDC solenoid valves (0.3W &7w)would these require interposing relays as they are within the limits of the channel?
Thanks
RE: Inter posing relay
One thing to look out for is the total Amp. on the card.
Usually for one 8xOut card it is usually 2 Amps, so they are constructed for valves with 2 coils on one valve so only one side is active at the time.
If you need different power sources like safety or regular control there can be interposing relays if it is a rebuild in a old facilities, but in a new ones you put emergency stopped valves on one card safety or standard and regular controlled on another with a separate feeds.
BR A
“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein
RE: Inter posing relay
Brad Waybright
The more you know, the more you know you don't know.
RE: Inter posing relay
For the 6ES7132-4BD02-0AA0 ET200S 4DO 24VDC 0,5A the total is 2A.
But for 16DO or 8DO it is not always the case, so it is best to check it in the manual for the card to be sure.
Best Regards A
“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein
RE: Inter posing relay
-AK2DM
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"It's the questions that drive us"
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RE: Inter posing relay
RE: Inter posing relay
RE: Inter posing relay
The unpopularity stems from this: it ends up costing more to add the relays and it takes more space in the control panel. But from my experience any perceived savings in going direct to the card can be wiped out in an instant when the card fails and you don't have one on the shelf, or even if you do, it involves a complete shutdown and more lost production to replace it. I learned that lesson the hard way at a steel mill; welded relay output on a PLC card, replacement card was available, but in another building. By the time we got the card, shut down the PLC (no hot swap capability), replaced it and turned it back on, the crucible was ruined, cost us over $50k, and that was in 1978 dollars! The interposing relays and extra space in the panel would have been far far cheaper.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Inter posing relay
TTFN (ta ta for now)
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RE: Inter posing relay
Brad Waybright
The more you know, the more you know you don't know.
RE: Inter posing relay
An interposing relay on a PLC output would never need to have the wiring changed or moved, it just mirrors the PLC output, protecting it from the ravages of the real world wiring. As a bonus, I sometimes used the little "ice cube" relays that have a push button or lever to manually force the contacts, those can be really handy for troubleshooting. I had a couple of years working as a System Integrator for a company that did prison systems, all of the door locks were controlled by PLCs. We had interposing relays for every output because the solenoids on the door locks were tough duty for the PLC relay card and if the relay contact welded, it resulted in the door lock being unlatched. In some of those prisons, that would be REALLY bad... When it happened, the guards knew they could reach in and pull the relay, which would drop out the solenoid and re-latch the door.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Inter posing relay
"The pump isn't running and I think it should be."
"Go to the relay labeled PMP and lift the little flat flipper thing on it. Did the pump run?"
"No"
"There's not a problem with your PLC. The problem is with the pump."
Keith Cress
kcress - http://www.flaminsystems.com
RE: Inter posing relay
I will agree to disagree.
Brad Waybright
The more you know, the more you know you don't know.
RE: Inter posing relay
Most systems I would build without interposing relays, but then I am as much a PLC and automation programmer as I am a maintenance electrician.
There could be situations as some here describes where they are a necessity.
And in some cases it might be better for the end user.
Where I work we would never put them in if not absolutely necessary and takes them away as soon as we get the chance.
All our electricians make there troubleshooting with the PLC, having interposing relays or other relay systems that coexist with the PLC makes two systems to troubleshoot.
Which makes them very confused
And since I am the only one that is old enough
I end up having to take care of the relay problems...
The most common brand of PLC system we use, I can't remember having to change more then maybe 2 or 3 cards in 30 years and we have many.
/A
“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein
RE: Inter posing relay
I was just gonna say that.
In my (many years) experience, I've seen MOVs used on AC outputs but have never specified them myself. Either way I can't remember having an AC ouput fail unless it is used outside it's specified rating, or when not individually fuse protected and closing into a short. I have cooked a couple of DC outputs when switching into a larger inductive load which can be prevented by using a free wheeling diode.
Keith--
I would expect that if my customer's maintenance had appropriate NFPA70E training, then they should have personnel able to identify whether a particular PLC output was on. If they didn't then they probably shouldn't be opening the control panel anyway.
Again, that's just my opinion.
Brad Waybright
The more you know, the more you know you don't know.
RE: Inter posing relay
I prefer to use varistors for DC and RC circuits for AC.
Free wheeling diodes that has become "popular" is half good at both but not good enough, in my experience.
On valves a ordinary diod of the right size does the job much better then most products you can buy ready made.
/A
“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein
RE: Inter posing relay
Knowing a number of people I have worked with ... I'd be voting for interposing relays.
Example - I was debugging a mechanical failure and required the use of a system controller and a motor amplifier. It was a constant fight to get this done as various pieces of test equipment kept getting taken to higher priority work**. I did not have an office I could lock it all away - it was about 200 pounds and bulky. You'd think a lab with a cypher-lock was enough.
Imagine my surprise when my red-tagged motor amplifier goes missing - it had been removed from production because the maker had made some change and the DoD didn't want the prototype installed. Where was it? Stolen back by production. They had done work over the weekend and burned up every production amplifier, one after the other. Here's $5k*, here's another $5k, here's another $5k; all of them. So they took my scavanged unit which didn't have the new mod and, apparently, were more than willing to burn that one too.
*Cost to repair. In working condition they were more than that.
**Higher priority meant - cash flow. The mechanical problem was worrying over safety of flight, but hadn't failed completely yet.
RE: Inter posing relay
What protection.
And where comes the relays in to the picture.
/A
“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein
RE: Inter posing relay
Only qualified employees may work in areas containing unguarded, uninsulated energized lines or parts of equipment operating at 50 volts or more.
This means unqualified personnel SHALL not open a control panel with a 120 volt terminal in it.
Just sayin'...
Brad Waybright
The more you know, the more you know you don't know.
RE: Inter posing relay
I've seen a dozen failed PLC relay outputs and only one failed SS output.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Inter posing relay
RE: Inter posing relay
Don't go there. A couple of weeks ago I received a call about a problem at the plant. I was pretty sure I knew what it was and called the electrician to check it out. He reported back that everything I had him check was fine so I had to go in. I discovered that he was looking in the wrong control panel.
Brad Waybright
The more you know, the more you know you don't know.
RE: Inter posing relay
danw2 then you are using the wrong PLC cards, the ones we have used for the last twenty years, you exchange as easily as a relay it's just plug and play.
But we never have to.
/A
“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein
RE: Inter posing relay
There have also been improvements in automation equipment over the years that make replacement easier (pluggable terminals for each PLC card as an example), and there's also the cost, both in equipment and assembly for the panels to include the additional relays. My preference is generally additional relays, as it's then possible to run with a single type of output card, and everything else gets interposing relays or equipment suitably rated to drive whatever's at the other end.
EDMS Australia
RE: Inter posing relay
I use the term "Bubba". In my experience the worst maintenance tech in any given facility is invariably named (or nicknamed) Bubba. He has no neck, hands like meat hooks, fingers like sausages and a brain like Emmantaler cheese.
This guy is a Bubba...
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Inter posing relay
I have only come across one like that during my years, but his nickname was like "weld guru" and he was actually good at his job and he made great sponge cake.
/A
“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein