Losing voltage at E stop

[wade88]

Hi lads,ladies

I have just put together an E stop circuit that is integrated into an auger motor control circuit w/ forward/reverse DOL. I have posted this awful diagram on another post but i am having some trouble when i put 24v down the + line and getting a readying of 0V as soon as it hits the first E stop.

I just drew this up really quickly yesterday to give a better idea of what im looking at.



The 24V signal will actually be supplied by the PLC module, but the PLC chap has yet to come in and finish off his work so i wanted to just test mt circuit prior to his arrival and put 24v down the line. I was getting a voltage until it hit the first E stop which is located on the side of the auger hopper.



I have a 24v DC mini contactor relay in the adaptable box with the E stop circuit coming from the A1 and A2 ports in tri-rated 18AWG cable, the circuit continues round to the second E stop the other side of the hopper and then will carry on to the PLC when its ready. When the PLC calls for product it will send the 24V signal through the line, through the E stops and onto the contactor, energising the coil and closing the circuit. That's the plan

But like i mentioned, even after putting 24V down it, simulating the PLC signal, when it hits the first E stop, i just lose voltage, and get nothing?

This isn't the sort of work i do everyday, and is my first E stop circuit. I posted previously regarding this topic and received from very useful feedback from a lot of guys regarding its design etc, so would really appreciated a little more on this matter.

Am i missing something really obvious, i may have missed a lot out in the description so i apologise if your short on info. Just ask and i shall try and answer you.

Cheers lads, Ben

 

[wade88]

Be gentle Tony

 

[Spoon]

I take it that you have done it this way cause the rist assessment says there is no risk to human injury?
I also take it that there are N/C contacts on the stop buttons and not N/O, as shown in your diagram?

 

[Fast&Rough]

You should put the e-stops in with the start stop controll that brings in the contactors instead of adding in another contactor. what else is the plc controlling its usualy just an input sent back to the plc giving an Id on which e-stop has been activated

 

[wade88]

Yes N/C contacts, Im a bit of a boob, but not a total ---

I personally believe there is little to no risk of human injury yes after carrying out my own risk assessment. But wanted to put the E stops in anyway. Should i have done it another way?

 

[wade88]

You should put the e-stops in with the start stop controll that brings in the contactors instead of adding in another contactor. what else is the plc controlling its usualy just an input sent back to the plc giving an Id on which e-stop has been activated

Yes that was the original plan, but the start stop control as pictured, which is what we wanted, was not available with a 24v coil.

 

[Spoon]

Are the guards Fixed or Interlocked?
If all is well with the risk assessment then you only need to use one of the two N/C contacts on the EM stop buttons.
Scrap the ones off in black and then try again. Check the continuity of the contacts to see if they are ok and functioning correctly.

 

[Spoon]

I think what F&R is getting at is to put the EM stop contact in series with the Stop button on the start/stop.
That would have been better.

 

[wade88]

Well i have wired them as such, + to terminal "1", - to terminal "2" and so one then just daisy chained on to E stop number 2, same terminations in that switch (only using one of the N/C contacts on each E stop) and then out to the PLC.

 

[Spoon]

Are the guards Fixed or Interlocked? Important question.
So you have 4 EM Stop Pushbuttons. Is it wires like this: (done in a rush)

 

[stef]

Yes that was the original plan, but the start stop control as pictured, which is what we wanted, was not available with a 24v coil.

Careful with that, wade, look at the machine safety directive: safety has to be separated from start/stop circuit, if it is a new design you must include a failsafe device. Therefore a second contactor is needed, one for the safety, one for start/stop. I was in a similar dilemma a while ago, Tony gave me some excellent advice. To cover your own butt, make sure that you are compliant, whatever you do.

 

[Silly Sausage]

Be gentle Tony

I do like an optimist!

 

[Fast&Rough]

Pilz 2 channel safety relay

 

[wade88]

Careful with that, wade, look at the machine safety directive: safety has to be separated from start/stop circuit, if it is a new design you must include a failsafe device. Therefore a second contactor is needed, one for the safety, one for start/stop. I was in a similar dilemma a while ago, Tony gave me some excellent advice. To cover your own butt, make sure that you are compliant, whatever you do.

It is a seperate contactor for the safety circuit mate. Main start/stop contactor is in the main box.

Spoon, thanks for making better clarity of my awful drawing, i have 2 e stops, i just drew it badly as i don't know the correct way to drawy diagrams i apologise. So i only need to take one feed from A1 across the E stops? and then take that feed back to the PLC? I just assumed i needed a + and -. my inexperience getting the better of me again.

 

[KAS1]

That cable tray is ****...e

 

[wade88]

I think i have been a total fool. I have over looked the insanely obvious....... i shall take myself outside and beat myself with a cricket bat.

 

[Silly Sausage]

I applaud your thread timing Ben....during Tony's afternoon nap! :smilielol5:

 

[Robotstar5]

I'd replace the contactor with a safety contactor, use an N/C aux contact in the reset line of a safety relay. The safety relay would monitor the E-stops and the PLC feed to the contactor coil would go through one of the safety outputs, 13-14 etc.

 

[Brightspark2]

To improve the tray mount it on brackets rather than straight to the wall, then you can get cable ties behind. Also manufacturer the top bend rather than just sticking two piece's side by side. Will look a lot better and more professional.

Now I'm not calling your work as I don't like doing that, its just tips for next time :daisy:

 

[vaughant]

Wade don't wind yourself up about it mate,a basic stop start circuit is a question my boss (now former) added to the archer trade test and apparently the majority of sparks got it wrong,which for a control man like me is scary but then again I'd never made off a barrier gland until my last trip offshore so it's different horses for different courses.

But basically your e-stops are just a daisy chain in line to your a1 or coil + on the contactor.

Generally pilz style relays are used as its harder to bypass them but not impossible.

 

[Knobhead]

I applaud your thread timing Ben....during Tony's afternoon nap! :smilielol5:

I'm awake now, unfortunately it's 02:00! I'm not even going to comment on this travesty. I just hope it doesn't develop in to a tragedy!

 

[wade88]

Yay Tony's here!

Brightspark, i did mount the tray on spacers, you just can't see them. As for the top bend, it's pretty ugly for sure. Bit of a tray noob, so ill do a better job next time.

Vaughant, thanks mate, i've got it down now, made a really silly error, really face slapping moment, but it's all good now.

Robostar, due to my lack of experience in this area, i didnt think to look to get a dedicated safety contactor, figured the one i have would suffice (which it will) although i appreciate it is not idea for the scenario, i will source a new contactor asap


Thanks again lads, really appreciate the feedback...and you tony, big kisses

 

[Spoon]

I thought one of your work mates was going to help with the design of this? One that has lots of experience in machine safety directive and safety circuits?
Again (just cause I curious and it is important) are the mesh guards on the mixer fixed (Bolted closed) or hinged (for maintenance)?
If there has been a full safety report and there is no chance of injury to people do you still need an Emergency Stop circuit? Could you just not use a Stop Circuit?

I quite understand why Tony is not saying anything.... I hope you are being supervised by your work mate who has experience in machine safety directive and safety circuits

 

[wade88]

My colleague is from a different company, he came down for a day to help me with a bucket lift conveyor i was having some issues with and then talked me through the design of this.

It's ok, i understand why people may be dubious to make comment, thats fine.

Bolted closed mate.

 

[Spoon]

Im just trying to help you out a bit mate and hope that you dont end up getting yourself into lots of trouble if things go wrong.
Its good that the guards are bolted closed.
When you did your risk assessment what Category of stop was needed for your design?

 

[wade88]

Yea and i appreciate it fella for sure.

Not really sure what you mean by category of E stop Spoon, like i said, new to this area, but i decided after writing the SOP for the process and scrutinising it, although i dont necessarily feel E stops are essential, if i am honest i weanted to put them in because i never have before and wanted to give it a go and couldn't see the harm in doing so, but i opted for standard, latching, twist reset E stops.

Again, I can only apologise that my threads may wind the veterans amongst you lot up no end, but i have no where else to turn for help on these matters than this forum quite honestly, and although thats a rather scary prospect and 95% of you guys wil have just sighed in desperation, i still feel that by coming here and asking my stupid questions, at least its better than not asking, not knowing what i am doing, and just doing it wrong..... wronger....

I am not a total plank, i promise, im quite competent, but there are many many things for me to learn, i am just trying to do that, albeit a little unorthodox.

 

[vaughant]

Yea and i appreciate it fella for sure.

Not really sure what you mean by category of E stop Spoon, like i said, new to this area, but i decided after writing the SOP for the process and scrutinising it, although i dont necessarily feel E stops are essential, if i am honest i weanted to put them in because i never have before and wanted to give it a go and couldn't see the harm in doing so, but i opted for standard, latching, twist reset E stops.

Again, I can only apologise that my threads may wind the veterans amongst you lot up no end, but i have no where else to turn for help on these matters than this forum quite honestly, and although thats a rather scary prospect and 95% of you guys wil have just sighed in desperation, i still feel that by coming here and asking my stupid questions, at least its better than not asking, not knowing what i am doing, and just doing it wrong..... wronger....

I am not a total plank, i promise, im quite competent, but there are many many things for me to learn, i am just trying to do that, albeit a little unorthodox.

Nothing wrong with asking fella but you will always receive some aghast replies as really in a control style apprenticeship like I (and no doubt many others in this section) did,the first thing you learn about any machine is how to stop it and then how to start it.
The safety circuit is always the first part of pretty much any control design because the idea being when you hit the "big red button" you cut everything off as you don't know in that split second whether there's a jammed hand,split hydraulic hose under pressure,burning motor etc,you just know you want the whole machine to stop there and then hence the importance of it and in all honesty it's good to see your trying to incorporate that into your work,but be aware there's a LOT to the safety side of it and there's some really clever bits of kit out there which make it safer for the operator which is what it's all about really.
In ford even the majority of bolted guards had limit switches on them directly linked to some sort of safety device as someone got crushed in another plant by opening a fixed door while the machine was running.
No safety system is 100% foolproof,but it's designed to make you think about why your bypassing it,which often you have to in a controlled environment,rather than just jumping in head first.
I think it's a bit like when the more installation biased sparks get very wound up when folk don't use the correct size earthing etc,I've found in most industries where I've worked it's a case of "use what we've got" rather than always using the exact for the job,often it tends to be larger than required but this is not always the case.

 

[Spoon]

Not really sure what you mean by category of E stop Spoon,

Have a read of this.
View attachment Risk_Assessment.pdf

 

[wade88]

Thanks guys. Spoon, thats great, i have printed that off and bound it into my H&S folder, i am attending a NEBOSH International Cert course next month, so that will definitely give me a good leg up on all of this.

The risk assessments i carry out are based around the guidance provided and templates available online at HSE: Information about health and safety at work as thats been my only point of reference since doing this job.

Good news it however, i just tested the circuit, and it all works fine. Start/stop, the main E stop, forward reverse and all my E stops on the hopper all work. So im pretty pleased with that.

Vaughant you are absolutely right on all accounts, i have no insisted at work here to have almost free rein on my own purchasing accounts so i buy what i want when i need/want it, to allow me to purchase the correct stuff for the job, as spoon has pointed out however and a few others, what i feel is right for the job, may be and often probably isnt, but what i have got this time is working, and it is all safe.


In time and as a gather more experience, i will pick these things up along the way i guess.

Thanks again everyone

 

[KAS1]

I remember when people would employee a design engineer to do the electrical design work (if the inexperienced trainee / electrician wasn't up to it) and then install the electrical installation to a spec lol