We have conveyors and racks with up to 9 estops along the line, but only two actually work. The others do not work. I am trying to find a diagram on how to wire them all up together so anyone of them can shut down the line. But I haven't been able to find one. Can someone point me in the right direction they are low voltage E.STOPS connected to a Mitsubishi PLC.
How are the e-stops wired? You need to make sure that all of the estops are wired in series with one another and that when each e-stop is pressed the contacts are opening on that e-stop, breaking the circuit.
How is the PLC wired? Is each e-stop wired back to its own PLC terminal point, or are the E-stops wired together and only 1 wire coming back to land on the PLC? Sounds like to me you may have multiple groups of e-stops coming back to the PLC.
Let us know what you find, and if you can give more details in what you have found in the field ex. how the switches are wired back to the plc. Also, is the plc receiving the signal when an e-stop is pressed. That could give us a better idea of what's going on.
Does all of this make sense? If not what parts, so that it can be further explained.
Sorry for taking so long, they are wired up in a series. the end to end is connected to N24 that's the 24V. the other end that connects to each E.STOP is connected to the PLC. 3 of them are on PX022 and 3 of them are on PX024, but none of them work. Can we upload pictures here. if so I can get a snap of the diagram if it would help.
Here is the diagram:
Having e-stops on a conveyor that don't work is pretty risky, what if someone gets hurt?
I have never seen e-stops wired through a PLC, not to say they can't be. I'm guessing the PLC has 24 VDC inputs. With a long conveyor, I'm guessing 1000 yards, I don't think AC inputs would work.
It might be possible to get AC inputs to work by loading them down with a resistor effectively making it a current loop rather than Voltage.
If each stop is wired back to it's own dedicated input then you would be able to point to the one that's pulled however in my experience they are usually in series.
Can you give us some more information like how many inputs, Voltage, AC or DC?
I haven't worked on conveyors for quite a while, but I seem to recall there are special relays available for the switch/control system interface.
I found this forum topic fairly informative
Really depends on your system, most e-stop systems are wired in series and very basic. However there are network type systems which I have no experience with. The prints are supposed to be in electrical control cabinet. I do believe your system is in serious violation. if you're inspected or someone gets injured, your company will be fined big time. call the OME for diagrams if none available.
I've recently followed a course about machine-safety (European standards). I don't know which standard (NFPA) you have to comply too. But I was told that hooking up a E-stop directly on to a non-safety PLC is a dead sin.
Use a safety-PLC (module) or Safety relays I was told.
without knowing more about what you actually have it is very hard to give you any advice. most such circuits are just contacts wired in series. it is a little disconcerting that such a simple circuit is not something you are familiar with. You probably should not be working on this kind of thing if you don't understand it. It is probably best if you find someone more knowledgeable to deal with the problem rather than trying to get random people on the Internet to help you. This is the kind of thing that might lead to someone getting injured or killed if not done correctly and it seems unlikely that you are the guy to get it done correctly.
As others have said, if it's an "e-stop" in the legal sense, what you have is probably not sufficient.
To be sure, you must do a proper risk assessment that identifies each hazard and its severity (measured multiple ways like frequency of exposure, level of potential injury, etc.). That will let you figure out the protection level you need, which will determine if your current circuit is adequate. If your conveyor doesn't have any exposed nip/pinch points and whatever is transported on the conveyor doesn't have much (if any) potential to hurt someone, you may be fine as-is. Otherwise, you're most likely in violation.
The above is NOT legal or safety advice. If you don't have the training/expertise to perform a proper risk assessment, hire someone who does. This is a big deal if OSHA ever comes to call.
I don't think we need a risk assessment study. We all know when you push or pull an emergency stop, the conveyor is supposed to stop. There's no question about that.
It is a matter of what is meant by e-Stop.
A simple PLC (non-redundant) shut-off does not qualify for man-safe stop. This particularly true with boilers, emergence stop or shutdowns in the petrochemical industry, or conveyor belts in manufacturing facilities.
In some cases double redundancy hardwired is insufficient, in other cases quintuple plc processor redundancy with hardwired over-rides is required.
Automation can be far more than simply trusting the plc to register when e-stops are pushed.
"I don't think we need a risk assessment study. We all know when you push or pull an emergency stop, the conveyor is supposed to stop. There's no question about that.*"*
What happens if there is a failure of of some sort such as the estop relay contacts welding closed? The risk assessment helps you decide how far to go in mitigating that kind of risk. You may do the risk assessment and decide that if you push the estop and the conveyor continues to move that is OK. Or you may decide it is not OK.
>I don't think we need a risk assessment study. We all know
>when you push or pull an emergency stop, the conveyor is
>supposed to stop. There's no question about that.
The risk assessment is to identify the hazards and how redundant/reliable your circuit has to be. Without that, anything we say here is pure speculation. Does it need to be category 3? Category 4? If either of those applies, the OP's circuit is NOT ok. If the risk is minuscule, he may be ok.
I don't believe you guys
The poster has a conveyor with 7 of the e-stop pulls not working and you think we should sit down and study it.
Fix the thing.
Presumably this is an old conveyor, and it worked once, are we going to go back now and study everything ever built in case it might not work?
I know how the big chemical companies do it, but they are only a part if industry worried because of some of the monumental screw-ups they made in the past.
...yeah, seems like some are missing the point that we are here to help each other out, and solve their problem. Not to tout about how much we know.
Well they have never worked since the lines were installed two-three years ago. A team came in from china to wire and program it. I don't know much about this stuff was just a mechanic here for the past 10 years now I have to try and figure this out. That's Y I am here to get some help is all. I had followed this diagram but it still seems to not shut the conveyor down.
We have 3 on the rack that stops the robot/module down but once you release the stop the robot starts moving again don't think it is supposed to do that. But at the moment I need to get the stops on the conveyor working can it be a programing issue since they are connected to the PLC
Here is the diagram:
I only see six stop switches, two sets of 3. Could be the input is not properly programmed for the set not working. Check your voltage and try a stop button to see if it opens the circuit, check LED for that input to see if it changes. The machine should not restart after release of stop button, you should have have a start button with time delay and warning buzzer.
Yeah I don't think it should work either. These are new additions to the old lines. The old lines when you push a stop, the robot stops and you have to restart it again, but the new ones are wired up and programed different. Will check the led on the PLC tomorrow when I get back to work to see if it is on or goes out.
Something a little odd about the whole section not working. Could it be as simple as a control cable not plugged in to join sections? Just thought i would throw it out there.
Yeah we looked into that; wasn't it.
>Something a little odd about the whole section not working.
>Could it be as simple as a control cable not plugged in to
>join sections? Just thought i would throw it out there.
The buttons are in two series groups.
I am used to emergency stops that are maintained. The operator has to reset them individually before the conveyor can be re-started. It looks as though these must be maintained by the logic.
If you can't look at the logic, at least for a start you can make sure each button kills the input PX022 or PX033. You should see the input light go out.
I wonder if someone has accidentally wired the stops in parallel instead of series.
Another test you can do is drop the wire off the PLC input killing it. That should stop the conveyor for sure. If it doesn't, there has to be something wrong with the programming. no?
We must have some Mitsubishi PLC guys on here who can comment on the configuration.
Can you take a close look at a stop switch and describe how it trips and how it is reset? Most conveyor switches I'm familiar with trip a mechanical latch when you pull the switch and need to be rotated to click back into the closed position.
Yeah we took off the wires on the PLC, and they keep running I was thinking. Then I thought, it can be that they either didn't activate either the input or the output for the stoppers as well. I would think they would need some kind of activation in the ladder. I do know how to check the program some, but the only computer with the software on it is in Chinese lol; working on getting one in English.
So this conveyor has been running for 2-3 years and its ES suddenly doesn't work or never work? I can see 2x 3series of ES there, so which one works?
Assuming this is 24VDC ES, for now you can check each ES first by push and release each one of them (will the open/close status changed or not).
if it is working properly, then check your looped connection from/to PLC IO module (means you check 2 groups of 3series ES signal to PLC). if it is also working properly, then check your PLC program (does the signal comes or not. I assume this chain of ESs never work if there is something wrong with the program, unless someone force the IO value and forgot to normalize it).
And also get a PLC guy to check this one.
Yeah hasn't worked since they installed, the lines but we have a new manager and he wants them all working. I saw that all but one line were never hooked up. they ran all the cables from the E.STOPS to the control box, but all they did was tie the cable back in the box never connected them to anything. Like I said before this is still new to me haven't done much with the electrical side of it.
Without the ladder or Logic drawing of the plc controls it is not possible to properly assess what is not working.
I have to say that my own experience has been that true "emergency stops" are not simply a plc input, but system over-rides that "stop" the system safely.
What you seem to have is a series of local stop switches, more properly classified as operator start/stops. They do not appear to be "man-safe" emergency stops.
Man not sure how I didn't see this before. I was looking at the diagram and noticed that this schematic is for the rack and not the conveyor. So they sent me the wrong one. Another thing is most of these new lines the stops were never connected in the control box. The cables are run there, but they are just not connected to anything. And the one that was connected to the PLC, the PLC for the numbers 22/23 screws are not lighting up at all like the other old lines are.
Well I appreciate you guys taking the time to help me but from what we found out was the program needs to be changed in order for them to work right. They are going to call in a programmer to fix the program.
Sounds like a good idea, hopefully he is local. You can get a local technician to correct your problem for less cost in many different ways. However, since it is a Safety circuit your issue needs to be carefully assessed and properly corrected. Good luck Sir, hope it works out for you.
Haven't seen a follow-up on your problem and I've been off-line for a while, so I'll throw my hat in the ring...
Short of a safety PLC or safety relay, your e-stops MUST be hard-wired. This means directly interrupting your motor control circuit. If you want any button to shut off all motors, your two strings of three must be wired as one string of six. Not knowing how your motors are wired is an issue for me. If they're cascading, stopping the first will stop them all IF there are no parallel start signals.
If you want your PLC to monitor your e-stops individually, you can add a 2nd dry contact to each button and have each button as an individual indicator of an e-stop condition.
Hope this helps...
Yeah we had to swap some weirs around, add a few relays, and adjust the program a bit to get it in order. Thanks for everyone's help it has been resolved.
When installing the E-Stop Safety Chain it is important to install a dual circuit that terminates at a Safety Relay or a Safety Controller such as the type manufactured by Banner. Having two circuits, run in series and running through all of the associated E-Stop switches with both contacts in the switch in a normally closed state, the ability to stop the conveyor safely as well as being in compliance with OSHA are both met. The PLC cannot be used as a safety device but can be used to monitor the status of the safety device (safety relay such as a Allen Bradley MSR127T in combination with a Banner IM-T-9A Interface module) by programming the PLC to report when the E-Stop circuit(s) have been disrupted.