Remote Stations and Light Curtains

Hey everyone!

Since last time everyone offered their help I am going to take advantage of your generosity again.

I am an intern on a manufacturing company. Ive been working on a machine addressing several performance and safety issues. Its composed of two remote IO stations and a local IO rack.

Lately one of the remote stations started blowing its fuse causing the parts of the machine that are connected to it to die pretty much. On this one in particular the input for the light curtain shuts down as well, thus unprotecting operators from getting in and suffer accidents since some rollers are connected to a different station and run independently.

I dont have much experience on this topic so now I have a couple of questions regarding this case:

1. was this the correct way to have my circuit wired up? (have the light curtain hooked up to a remote station that can blow up at any time)

2. should this safety inputs go to a separate station?

3. will it help moving this input from the remote station to the local rack?

4. is there any way to flag the program(like when someone breaks the light curtain) whenever a remote station shuts down?


This questions may seem nonsense for many of you but please understand my knowledge in this kind of issues is pretty basic.

Thanks again !

Ramiro

FYI, the remote station is a 1794-AENT FLEX I/O

I am not certain
Are you saying that the light curtains are running through a PLC only.
and not through a safety relay or controller?

I guess I am not certain either about your question.

One end of the light curtain is connected to vcc, thus sending light all the time. The other end is connected to a remote input that goes to the ethernet card on the local rack through a cable. The plc program will then ask for the state of the input in order to pull up the warning message(of course when that station is killed, so is the input and so the chance of getting an error warning if you break into the machine)

You should really seek help with this project - you do not want to be responsible for someone getting injured or even killed.

The light curtain must be hard wired through a safety relay to immediately kill any required motion when the curtain is broken. It should also be wired fail-safe so if the connection is broken the machine will also stop.

You can not do any kind of safety through remote I/O.

I agree with gbeaker, you should seek kelp.

Since you are an intern, you need direction from your superior.

there should be a risk assessment.
if the light curtain dies when the fuse blows and the operators are exposed to other parts of the machine that are running, then the design is flawed.

I do not know the particulars of your application, but I would seek help. you do not need to responsible for an accident or death.

regards,
james

Let's answer these questions directly.

1. Was this the correct way to have my circuit wired up? (have the light curtain hooked up to a remote station that can blow up at any time)

Click to expand...

This was the incorrect way to connect the light curtain. Safety inputs should never go into a remote I/O unit on a network unless that station is using special Safety inputs and the controller is a special Safety controller.

2. Should this safety inputs go to a separate station?

Click to expand...

Not unless that separate station has special Safety I/O modules and is connected to a Safety controller.

3. Will it help moving this input from the remote station to the local rack?

Click to expand...

Not really. It still will be using a general-purpose programmable device, and that's just fundamentally not a Safety circuit.

4. Is there any way to flag the program (like when someone breaks the light curtain) whenever a remote station shuts down?

Click to expand...

Finally, a Yes ! The controller almost certainly has a Rack Fault or Module Fault bit or tag that will tell you if the remote adapter or module has failed to communicate to the controller. Post details on the controller and network type and we can talk about this feature. It won't be really applicable to this safety application, but I/O module or network diagnostics is important stuff for ordinary machine programming.

Machine safety is a big topic, and in the USA it's confusing because you really only have OSHA regulations to guide you on specific types of machinery. Everthing else is vague and either points you toward a handful of industry standards (like in refining or robotics), towards a European or other global standard, or just to the basic principle of 'whatever doesn't get us sued'.

Hazard analysis and machine safety consulting are A Thing. There are guys whose whole career consists of analyzing everything that can go wrong with a machine and finding ways to prevent or detect it.

Take a step back and try to wrap your head around the whole operation of the system and the interconnections between systems.

Don't take "we've always done it that way" or "a conduit run costs too much" as final answers. Safety circuits are almost always hardwired and cost a lot more than general-purpose circuits because they're relied upon to keep everybody going home in one piece at the end of the day.

Thank you so much. I will track everything of what you just told me and make sure that the light curtain is effectively connected to a safety relay on that remote station.

Ok, so I just went down to the remote station and traced the whole thing. It seems to be protected as there are two safety relays(details are on the attached pictures).

What concerns me is that this whole station is only connected through an ethernet wire which goes to a switch and period. It is then my understanding that this is not connected to a safety circuit(what do you mean by safety circuit?)

I am sorry to ask these questions but my superior would barely pay attention to the stuff im asked to work on and it would be a waste of time.

Thank you

All this shows is that there's something wired up locally to the light curtain as a safety feature. Obviously I don't know the first thing about the system or how it's wired or its hazards, so this is not engineering advice.

The yellow box is the Datalogic light curtain control module. Light curtains have features like muting and blocking and self-test and alignment, so most of them have a control box like this one. The outputs from that module are probably wired over to the red box.

The red Minotaur relay is a "safety relay". It provides functions like external contactor monitoring and dual-channel inputs.

You can read all about it here: [MSR-09T Installation Instructions]

Your next step is to trace out the wiring on that safety relay. It's probably interrupting *something*, so you get to figure out exactly what that is.

Trace out what's connected to the safety outputs of the MSR09T; that's terminals 14 and 24.

If those only go to an input point on the FLEX I/O... then the safety relay isn't doing much !

the photos show a lot of information.
I can only make an asumption because I would need to see a wiring diagram.
there are two safety relays present
the Yellow one is a 'SICK' relay which may do the E/stops and the guard switches.
the Red Guardmaster controller should be Light curtain controller.
both these units have dual safety rated outputs.
they should not switch via the PLC although they may have a additional input to let the program know the guard status.
it is possible that the 'Guarded' Safey output may control the supply voltage to the outputs of the PLC
the rest is a guess.
the FLEX PLC is not a safety device.
As far as guarding a device when in maintenance situation.
I agree with the requirement to 'unbolt'.
Signs/stickers are great but may fall off or get damaged.
I would still use them.
If a switch is already fitted then make sure it is a safety type switch.
If the machine came with it then don't remove it.
Written operational procedures - Job Safety Procedure sheet.
is the method for maintenance.
If unbolting is for production/tool change, then consider the fact.
PEOPLE TAKE SHORTCUTS - "IT SAVES TIME"
This is usually the case after someone has been injured

foot note
I just read your post attachment KEN
THe Guard master is the Safety relay
the SICK unit will be the controller

SORRY
Ken is right