Student needs help

[FrostedFlake]

First off, I'm glad to see something like this up for PLC users. Second, i have a problem.

I am a student attending a Vocational School In Massachusetts, Old Colony RVTHS. I'm in the Electronics Shop, and we're doing a project.

The Project is a Rube Goldberg device, a series of chain reactions leading to a final goal. We've made it so that the goal in to start up a PLC. That's where we have a problem.

The PLC is supposed to light up a sign that says "BREAKFAST!"
that we made using LEDs and Perf-Board. We have the LED sign working well, but the program for the PLC is messed up somewhere...

We don't know how the outputs work on it. The Program lights up each of the five sections of the Sign, then turns off, then repeats the pattern over a period of 12 seconds.

For some reason, however, the outputs do not turn on. There's nothing coming out of the outputds at all. We have the program running, but there simply isn't anything coming out of the outputs. I don't know if you actually have to bring power to the ouputs because they work like switches, or something else, but I'm utterly lost here.

The PLC is a Mitsubishi MELSEC FXon-024 MT-DSS Transistor Unit. Any help would gladly be appreciated.

 

[Steve Bailey]

I don't know that particular product, but in general you need to furnish external power for PLC outputs.

 

[FrostedFlake]

Well, I AM Powering the PLC with 24VDC, like it needs, but does tham mean I need to apply power to the outputs? If so, does that mean they act like switches?

 

[yfcarer]

As steve bailey mentioned, you can try to suply aditional power for the LED. Usually, the output is not powerful enough to light a indicator, in that case, I use a real relay.
Hope can help.

 

[yfcarer]

Well, I AM Powering the PLC with 24VDC, like it needs, but does tham mean I need to apply power to the outputs? If so, does that mean they act like switches?

Yes, I think the DO output is just like a switch.

 

[Jimmie_Ohio]

I agree with Steve...

Also, I do have some general suggestions for project implementation in the future:

1) Be sure you have wiring diagrams for each and every piece of equipment you have in your system.

2) Before ever applying power to your electrical equipment, perform continuity checks on the wiring. If possible, do this as you go so you aren't troubleshooting a "bird's nest" of wiring.

3) Power up devices in some kind of order. If you have several circuit breakers protecting equipment, go through one power feed at a time. Don't forget to be sure the neutrals / commons are continuous throughout. I have seen several "daisy-chains" missing one connection, typically from the panel to the enclosure door.

4) Check your inputs into the PLC WITHOUT A PROGRAM LOADED.

5) Force your outputs from the PLC WITHOUT A PROGRAM LOADED.

6) Load your program and de-bug it RUNG-BY-RUNG.

An orderly check-out is a huge time-saver. As a student, you need to develop a good routine for this.

 

[gtsuport]

Is the Run light on?

Go to www.meau.com and download the manual for the plc. This will give you the wiring diagram for the unit.

 

[FrostedFlake]

Alright. Thank you for the assistance guys. I have another question now. There are two rows of Outputs on the PLC. 0v, 24v, a pair of black dots, and V0-11, and Y0-11. Where do I apply the voltage to run the outputs?

 

[Tom Jenkins]

OK, at this point in time you need to do two things:

First, get the manual for the PLC. It will have wiring diagrams for the outputs, and you need to wire your unit as shown. The details vary with every PLC model and card type out there, so general advice is dangerous. After you do the wiring, have your instructor check it before you power up anything.

Second, you need to think in terms of the First Law of thermodynamics while you are wiring this up. The sign needs energy to light up, and the energy has to come from somewhere and be controlled somehow. Keep this in mind as you are wiring the system, and follow the energy flow.

 

[Fox]

Please check Mitsubishi manual.

The black dots are for unused terminals; The Yn are the active outputs; the Vn or COMn are the points where 24VDC should be applied.

The 0V should be the common for your display in order to close the circuit.