Safety Relays

minzabud

I've recently taken up a maintenance position having come back from a couple of years travel, the factory im working in is much more hands on machinery with a lot of separate 3phase motors and independent machinery, manually operated.Im blowing off the cobwebs having been out of the trade and enjoying learning and the responsibility however I've been caught out with safety relays a couple of times this week and don't have any experience working/fault finding with them. For example I had an issue recently and found there to be no power at the relay, having seen other relays in the plant with a power light I went chasing for the feed but eventually found one of six magnet switches faulty which held the power out and in that time I replaced the relay with a different make and got lost in swapping them over.

What I'm looking to know is how they are normally used, what contacts should I be breaking through the relay? Invertor/Plc
Are all brands wired the same?
I've found the terminals confusing s33/s34 etc
Can I wire a push button e-stop in series with different types of switches and break through the relay?
Should I use more than one channel?
Do I bring a 24v supply to A1 and then loop into 13 and out on 14?

I always read any documentation with any parts but haven't got anything on the relays in use,
Any information or links to further reading much appreciated!

deandean

The main manufacturers of safety relays (Pilz and Schneider Electric come to mind) have some very good booklets on application, use and wiring of their products.

I suggest you get the mfr's info in the first instance, that'll probably sort you out.

They are fairly straightforward products. The key to a hassle free system is lots of diagnostics, e.g. use sensors and interlock switches with indicator lights .

crasy dash

Welcome back to trade first
Great place on here to ask your questions a lot of experienced guys on here.

Are you working on your own or part of a maintenance team?
First thing i would be looking at in the factory is the electrical drawings for the machines you will be working on.
Is there a copy of the electrical schematics in the panels where you find yourself working on?

Take them photocopy them for yourself learn to follow the contol sequence from where it is fed from what mcb fuse etc what voltages are used etc what proximity switches push buttons e-stops safety barriers etc are on the machine.

Often i find maybe spending a bit of time watching the machines being operated helps you understand what happens if x y or z happens or if an operator opens this door or turns this selector switch how the piece of plants reacts.


What type are industry are you now working in is is food production pharmeceutical etc

How is your understanding of the basics or d.o.l etc is it good or would you consider yourself rusty

The more information you can provide the better as the more experienced guys will be able to help you

minzabud

Thanks for the replies, from what I've seen so far there's nothing im really fazed by it's just a lot to take in initially so will take a bit of time, im also trying to manage there expectations as I am the only electrician working there and can be doing anything from changing light bulbs to mechanical work aswel as fault finding on panels, the long term fitters are quite clued in on most things in the plant and have no problem wiring in invertors etc but a lot of the repairs to panels are a bit agricultural so I will aim to change that, some of the motors are using rectifiers and different supply systems then I came across before so plenty of homework.

2011

This is a bit of a minefield to be honest. Changing one component for one that appears to be a similar component or the wiring can impact on the integrity and / or certification of the circuit.
I am not an expert in functional safety but, I will try to explain:

Following a risk assessment or HAZOP on a machine or a system it may be determined that a safety circuit (often referred to as a Safety Instrument System) is required. Further analysis is the required to set a "target". This target may be SIL 1, 2, 3 or 4 with four being the most stringent. Link: Safety Integrity Level. This is required to ensure compliance with IEC 61508 many factors have to be considered and complex calculations have to be carried out.

At work when we have to ensure that our design meets various SIL or PL (Performance Level) targets we employ a third party (such as Pilz) to verify the design. Once the safety system is deemed to meet the requirements changing of any component (unless like for like) or wiring arrangement invalidates the certification. A different relay may have a lower MTBF (Mean Time Between Failure) value, meaning that the circuit no longer meets the target set.

Similar components may have to be wired in parallel to ensure diversity so that the failure of one component will not lead to a dangerous failure of the machine or system.

In short, my point is don't go changing a safety relay in a plant for what appears to be an equivalent or change the way the circuit is wired without getting sign off from the appropriate manager / engineer.

Tuco88

This might help if its the hands on wiring side your interested, S33 is the rest set can't remember if its the Auto anway. ,https://www.youtube.com/watch?v=u3FkUMc5WWY I had a stiff learning curve also with these good luck.

minzabud

Thanks for that, I had seen that loop before and wondered about it.

I'm working on a new machine which has not been put in service yet, it came from China with no diagrams and the safety system needs to be upgraded as it just has a proximity switch on the door which can be easily bipasssd, I have replaced the switch with a magnetic type but for some reason it's constantly sending 24v back to the Plc so won't work that way, there is no safety relay in place at the moment so I will be putting one in for the one inspection door on the machine I just need to figure out the best way to do this as the the two contactors in the panel have 230v coils so maybe changing to 24v and going through the magnetic switch to cut the supply to the invertors would work best?

brightspark

Can you post the model of switch you are fitting.

Also you can't rely on the PLC for safety related purposes.

Be careful that you meet relevant standards for the safety of the equipment involved and the hazards present. As you are installing the new circuitry you may be the one in court if something goes wrong!

crasy dash

I would agree with brighspark op.

If I was you I would be reporting your concerns regarding the safety devices on the machine to your team lead or maintenance manager.

As brightspark said something goes wrong you are liable for altering the safety circuit.

HardenendMan

minzabud wrote: »

Thanks for that, I had seen that loop before and wondered about it.

I'm working on a new machine which has not been put in service yet, it came from China with no diagrams and the safety system needs to be upgraded as it just has a proximity switch on the door which can be easily bipasssd, I have replaced the switch with a magnetic type but for some reason it's constantly sending 24v back to the Plc so won't work that way, there is no safety relay in place at the moment so I will be putting one in for the one inspection door on the machine I just need to figure out the best way to do this as the the two contactors in the panel have 230v coils so maybe changing to 24v and going through the magnetic switch to cut the supply to the invertors would work best?

As others have said, be careful OP. It should not be your responsibility to upgrade a machine's safety system.

Have yee no engineering department that looks after this?

minzabud

I've have taken the points above on board and discussed it with the manager, they have a contractor for programming plcs and upgrading other equipment so I suggested we get him on board and would benefit me to go through it with him.

2011

minzabud wrote: »

I've have taken the points above on board and discussed it with the manager, they have a contractor for programming plcs and upgrading other equipment so I suggested we get him on board and would benefit me to go through it with him.

That could be a good starting point alright.
Perhaps they can dig out a wiring schematic or loop drawing for you.
Automation engineers generally have to have a good handel on how a system works.

Tuco88

Wreck his head with questions while you have the chance, it's what I always do.