AB 1769-OB16P DC output module, stupid question

Okay, so it's been a while since I have used one of these, I have the PLC configured properly, I am using an AC input module, a DC input module, and I have a basic program running. However, when I turn on Local3:O.0 I can see the LED turn yellow on the front of the module but no voltage comes out...do I need to wire 24VDC into the terminal block inside the module? I just assumed that it received its 24VDC from the PLC's power supply.

Any responses are very much appreciated. Thanks for reading!

SolarNinja said:

Okay, so it's been a while since I have used one of these, I have the PLC configured properly, I am using an AC input module, a DC input module, and I have a basic program running. However, when I turn on Local3:O.0 I can see the LED turn yellow on the front of the module but no voltage comes out...do I need to wire 24VDC into the terminal block inside the module? I just assumed that it received its 24VDC from the PLC's power supply.

Any responses are very much appreciated. Thanks for reading!

Click to expand...

It receives the signal from the PLC, but it uses external 24vdc connections for the actual outputs.

jacoffey85 said:

It receives the signal from the PLC, but it uses external 24vdc connections for the actual outputs.

Click to expand...

Also see wiring diagram if you don't have it. As jacoffey85 said apply your external power to "+VDC" terminal on the card.

See pdf

Posts two and three covered it, I just wanted to add that the reason for this is that the terminals are opto-isolated from the controller's backplane, hence requiring an external power source. This is a good thing for the controller and its PSU.

Awesome, thanks so much Mickey and JeremyM. I figured it was something along those lines since it appeared the module was not faulting and the light on the front of the module was lit indicating that it was passing power to the output. I will supply power and take it from there!

-Monte

Thanks Mickey for linking that wiring diagram. I am starting to wonder if I have a faulty module, but I feel like there is a higher probability that I am missing something. First let me make sure I understand this wiring diagram:

24VDC positive goes to +VDC. 24VDC negative goes to DC COM. The resistors and "CR" notations are there to indicate a load (I'm assuming the CR stands for contact relay). This is a sourcing output module so it's +VDC that is supplied to the load when the output becomes energized. That being said, with output 0 energized, I should be reading 24VDC between DC COM and OUTPUT 0.

Okay, assuming that I understand this wiring diagram correctly, and that I should be reading voltage and I am not, here are more details:

I am using the same 24VDC power supply to supply power to this module. The output module is the only draw (besides the PLC and modules) that is taking a load from this PS. The light that indicates an output is energized is amber in color. I am reading 24VDC across DC Com and +VDC. I think that's all the pertinent information. Please forgive me if I am making a stupid mistake. I have 3 more output modules so I may try swapping out another unit next. Will wait to see what responses I get here first. Thanks again for reading!

Can you try the card's other output points?

I would do like JeremyM said and test other outputs. If none are working, one simple thing to check would be the terminal strip on the front of the module. I've installed new modules where they weren't making good connection and have had similar issues.

Well JeremyM, thanks for your suggestion, I just turned on all of the outputs and LEARNED SOMETHING! The vastness of my expertise in practical electronics never ceases to amaze me...I learned today that the tops of the screws on the terminal board don't make for good contacts unless they are tightened down. Yes ladies and gentlemen, I am feeling very humble now. Problem solved, all outputs are working. Thanks all of you for your assistance! (PALM FACE MOMENT!...and I'm the guy who is supposed to be programming the fire protection system...god help us all!)

-Monte

The resistors and "CR" notations are there to indicate a load (I'm assuming the CR stands for contact relay).

Click to expand...

FYI, the symbol you call a resistor is a symbol for a solenoid and the "CR" is a control relay.

and I'm the guy who is supposed to be programming the fire protection system...god help us all!)

Click to expand...

I hope you are NOT trying to use a PLC for fire protection control.
There are dedicated systems for this kind of control.

I am using special IR sensors for a low pressure system (.9" W.C.) used per manufacturer's recommendation...al they need to do is detect spark and open a water feed later down the duct...then leave the duct open until NEITHER bank of spark sensors see a spark for a period of 5 seconds. I am allowing .4 seconds for solenoid to energize to begin spraying water (more than enough headroom) and allowing for a max spark velocity of 3500 f/min. Yes, there is a dedicated system, which we have, but it is old, and the system is SIMPLE. I can set it up to auto test the spark sensors, I will be testing it with ACTUAL sparks (initially) and plenty of redundancy (abort gate, water suppression valves which operate at 90 PSI, pressure sensors and alarms for anything out of the ordinary. What is the problem with using a spark sensor to detect a spark then turning on the suppressors or abort gate? Don't tell me it's some kind of licensing/code/liability issue. We just need to have something that works. What I am doing seems reasonable to me.

The problem is not the sensors its the PLC. Your PLC is not a safety device.

And yes there may be "licensing/code/liability issue"(insurance). I am not an expert on this though.

Maybe someone else will jump in. I would definitely check though, if I where you.

PLC's control nuclear reactors. True, there are probably a ton of redundancy systems in a nuclear reactor, and there are many safety sub-systems that are in play, but they all tie in with PLC's. Mickey, I am trying to visualize a circumstance where a PLC is not "safe"...a situation where the program will not protect against fire. Thus far, every single circumstance that I can foresee can be handled by redundancy programmed into the PLC.

(1) sensors faulting (prevented by periodic automatic sensor tests)
(2) PLC shut down (make an alarm happen if PLC faults)
(3) Suppression actuators not functioning (monthly actuator checks, this may not seem ideal, but that's the same way the dedicated fire safety system works...there is no way to "test" them without physically turning them on and making sure water is coming out)

...you get the picture. I can't see a damaging event or failure that cannot be solved by redundancy. The fire system that we have is rebuilt, so it should be operational and "safe", but I didn't build the thing, so I can't work on it. Plus, electronic components fail. PLC, if you adhere to the ISA-88 standard, can be worked on by any competent ladder logic programmer. True, years of R&D went into these fire safety systems, but you have to think, they make a **** ton of money on these systems, for something that performs a relatively simple task. If they switched to PLC systems, and I can see why they would not want to do so, they wouldn't make NEARLY as much money. And money, my friend, is the whole reason they are in business. Code and licenses aside, I want something that WORKS, is PRACTICAL, and SERVICEABLE. I am cautious with this project, as you are the second person to tell me that this is not a job for a PLC (the other person was an engineer at the company that manufactures the spark detection sensors so I keep in mind he wants me to buy into his system) but so far no one has given me any reason why not. The PLC seems far superior in every way than a bunch of hardware that can fail at any point just as easily as the PLC. That being said I very much welcome and value ANYTHING anyone has to say on the subject. Perhaps I should start a new thread...

Try reading this in a weekend:

http://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards

Can your system meet this? Are you prepared to assume liability?

Ummmmm.... Ever feel that cold air of lack of safety creep up on you in the middle of the night?