Remote E Stop Solution

Hi,

We have been asked to specify a remote E-stop solution for a client.

They have 2 sites (so far) and each site has a main control room with 3 Hard wired E-Stops (Mushroom Buttons) located next to the operator's desk. The E-Stops are wired to 3 separate safety PLC's for tripping the respective system.

The plan is to centralize control of the 2 sites at a remote location (Central Control Room) so we need to provide these 3 E-Stops (6 Total) at the new control room.

Not being too familiar with safety systems, I was curious about what other people have done for this scenario.

The plan so far is to simply 'cut in' to the E-Stop circuits and install Remote IO with Relay outputs, then install a PLC at the Central Control Room with new mushroom buttons connected to DI's.
I was thinking of a GuardLogix PLC in the control room with Safety Guard Point IO on site but I'm wondering if we could just use a programmable safety relay - I can't determine from what I've read whether the safety relay is intended to be used in this way e.g Remote IO.

This all seems quite complex for simply switching 3 relays remotely - if anyone has a simpler solution then I'd be keen to hear that too.

Thanks

http://www.plctalk.net/qanda/showthread.php?t=80949

http://www.plctalk.net/qanda/showthread.php?t=69246

Here are a couple of threads that may help you out.
Regards,

We have planned something similar. We haven't tested it remotely yet.

The plan is to use the existing GuardLogix Controllers that are already installed at the physical plant and only a single remote POINT Guard I/O rack via an Ethernet connection for the Emergency Stop buttons is connected at the remote control room.

Our concern is the update rate and the reliability of the connection.

I don't know of a safety relay that is designed for remote use. If you don't have GuardLogix PLC already in the system, you're right it does seem rather complex just to add a few buttons.

BEFORE you start !

you must look at the EU electrical / conformity rules & regulations, do a risk assessment with your safety team, and get in contact with your local authority.
An e-stop MUST be provided at various locations along the machine, not just in the control room. if someone can get caught in the machine, you need an e-stop to kill the power.

it's been a while since I have had to deal with your rules, but I don't think it is allowed. checking the rules and risk assessment will let you know.

regards,
james

When you say "remote location", are we talking just different areas at the same facility? Or are the sites in Christchurch and Hamilton, and they want a central control facility in Auckland?

Thanks for the responses.

The remote location is an hour's drive from the 2 sites - Not quite Christchurch to Auckland but I would think the same design considerations would apply.

With regard to the conformity and electrical regs, these E Stops are used to trigger ESD code within the PLC. They aren't used for electrical or mechanical interlocking like they would in a workshop or production line.
Do you know if there are applicable regs for this scenario?

Thanks

What do you mean by ESD code?


Presumably there will be a high speed link between both facilities and the control room. Theoretically, it would be possible to wire all the e/stops to a local safety PLC, use safety produced/consumed tags between the control room safety PLC and the remote safety PLC's to effect a safety function. I've done that before - although only between safety PLC's in the same factory, never between PLC's in physically separate locations. I definitely couldn't say for sure whether a produced/consumed tag would be stable or reliable enough across your link without testing. but if it is, then you can implement a completely safety rated system that way.


Regardless of which way you go, I'd suggest that you should 100% get someone involved in the project who has some kind of meaningful safety qualification. Even if they aren't any help with solving the distance problem, you need someone with the right letters after their name to look over your final solution and confirm it's suitable for its intended purpose. Otherwise, you as the designer are leaving yourself massively exposed should anything ever go wrong, even if it's not the fault of your solution.

ASF said:

What do you mean by ESD code?

Click to expand...

+1. It sounds like the current system is control based, rather than SIL or PL based. What are your sites doing? What are these buttons doing? There's a big difference between machine and process safety, for example.



AS4024 will give you the requirements for E-Stops, Risk Assessments, as well as any equipment specific requirements for items like presses, conveyors and robotics. If you plan on modifying the system, you will need to do a Risk Assessment, and meet the required Performance Level. This is the machine based standard.


As ASF posted - The hardware and architecture themselves will work if you have a stable WAN or Wireless connection, but there are too many details missing to comment further. My other red flag would be on the centralisation of the system. You have the potential to lose all your sites with a single failure. Is that acceptable?

Why not look at distributed safey systems form the likes of Beckhoff

Have estops on EtherCat linked to a SAFETY PLC at each location and then have a link via a VPN connection / Cloud etc. to link the Saftey PLC's .

beckhoff TwinSafe

SicknoteX said:

They have 2 sites (so far) and each site has a main control room with 3 Hard wired E-Stops (Mushroom Buttons) located next to the operator's desk. The E-Stops are wired to 3 separate safety PLC's for tripping the respective system.

Click to expand...

Wow, just wow. This is soooo wrong, as others have already stated.
1. An emergency stop button should be near the risk that it protects against. The relevant standards will specify the max distance allowed.
2. You cannot have multiple emergency stop buttons near to each other, when they have different stop functions. It doesnt matter if there are labels or similar to tell the operator which button to press. It is just not allowed.

I dont know the laws in New Zealand, but in the EU if you modify an existing safety system, it must be updated to the current standards. If an accident occurs, and you are found to have been negligent you can go to jail.
Same in the the US I believe.

You absolutely must get assistance from someone knowledgable in safety.

I came across this at a site and I just had to take a photo of it.
It is not made by me or my company, and I am not telling where it is.
So, if someone is about to be run over by a pick-and-place robot, you have to run over to the panel and press the right button. For real, no joke. Can anyone think of any problem with this design ? ......

JesperMP said:

Can anyone think of any problem with this design ? ......

Click to expand...

It is asymmetric. It needs another 2 buttons on the left.

Everyone is assuming machine guarding, but I have seen similar designs in chemical plants. Each E-stop shuts down an entire MCC building. The thinking is, IF, there is a major release, the operator hits the E-stops on the way out of the plant, killing all motors.

Ken Moore said:

Everyone is assuming machine guarding, but I have seen similar designs in chemical plants. Each E-stop shuts down an entire MCC building. The thinking is, IF, there is a major release, the operator hits the E-stops on the way out of the plant, killing all motors.

Click to expand...

This is exactly why I asked what the application was. Machine and process safety is very different, but the system still needs to meet the relevant SIL.

Ken Moore said:

Everyone is assuming machine guarding, but I have seen similar designs in chemical plants. Each E-stop shuts down an entire MCC building. The thinking is, IF, there is a major release, the operator hits the E-stops on the way out of the plant, killing all motors.

Click to expand...

That would still be 1 E-stops, not 3.
Edit: I admit I dont know much about chemical plant safety.