Normally open, Normally closed, ladder logic

[iant]

this is the problem osmanmom
if you use the E/STOP terminology people believe it is safe.
Always be careful how you word it.

The bigger issue is what happens when the E/STOP fails

@DOME1987 - search this site for safety relays
if this is an actual safety application

 

[osmanmom]

I understand fully iant,

not compromise on safety issue,

i want to he understand different between software and hardware,

what software can do if miss-use,

Ego and Stubborn

 

[FactoryTalktotheHand]

I think people are confused because you're using dual N/C contacts for your monitoring inputs and using two relays when these are usually reserved for the actual hard-wired safety circuit. If it's just for indication, you don't need to use two contacts for your E-Stop. You certainly can if you want to, but it's a waste of inputs. Use the two N/C contacts for the actual safety circuit and install a third N/O contact on the button if you can. Wire that N/O contact into the PLC and then it's as simple as:

        E-Stop N/O Input                    Indicating Lamp

-------------] [------------------------------(   )

Edit. Are you just designing something that tests the contacts in an E-Stop? As in temporarily hooking it up to confirm the functionality? If so, I wouldn't even bother with a PLC. Just get a safety relay, put it in a box, and wire up your test leads to it. PLCs lose their programs from time to time. Hard wired circuits don't. And if this isn't going to expand or change in the future, having a controller is just a waste of effort.

 

[osmanmom]

This is very good discussion

People around the world will get knowledge on our discussion.

Let them make decision.

What he need to do.

What’s it right and what’s wrong.

 

[dome1987]

Edit. Are you just designing something that tests the contacts in an E-Stop? As in temporarily hooking it up to confirm the functionality? If so, I wouldn't even bother with a PLC. Just get a safety relay, put it in a box, and wire up your test leads to it. PLCs lose their programs from time to time. Hard wired circuits don't. And if this isn't going to expand or change in the future, having a controller is just a waste of effort.

Its a different contacts from different controllers all of them have a emergency stop and the variety is expanding all the time. I think a plc would be the best option. How do i now how big plc i need like memory when the program is getting bigger and bigger?

 

[dome1987]

Thank you

Like to thank everyone that have joined the discussion and helped out with the questions.

Thank you so much i appreciate it

 

[MartinW]

A well designed safety system will have its own diagnostic coverage, and indeed MUST have to meet some performance levels.

A test of a safety function via non-safety equipment - which could lead to the perception that the safety function is working when it isn't - is not safe in my view and should be avoided at all costs.

If you need a system to check that the estop functionality is working, then you should have a safety related control system that has its own diagnostic checks.

I'm not an expert but I would not go anywhere near this. Also in the EU it makes no difference if you are manufacturing something for your own use (in-house) or something you are selling to a customer. The OP needs to take urgent advice on CE and compliance.

 

[duckman]

Dome, if you want some more help, please show a drawing of what you are trying to do. Showing the layout of the "Estop button and module" and how you are trying to test it and what you are hoping to achieve by wiring it into a PLC and what indication you are looking for in the Test producer.

 

[iant]

Dome - Most standard PLC's are not designed and they should never be used for safety operations
This is not the first time we have mentioned this to members on this site.

there are a few safety levels (description varies country to country)
SIL3 or Cat.4 are the highest of the ones I am familiar with.
Most PLC's do not have any rating - because they can easily be bypassed.
There are also some precise timing sequences.
THIS is the reason to use Safety Relays - They also monitor the output Safety contactors/relays in cct.

 

[duckman]

Hi Ian, remember a page or 2 ago you where saying it wasn't a safety issue? I like the other post you just answered were he's got 2 student projects on the go, at lest in the first he had a half plausible story(if you haven't heard it a few times). Time for you guys to start charging money if they haven't even used the search engine.

 

[iant]

the search engine will find all the previous posts on this site that People like myself have answered hundreds of times before.

but we still do

 

[iant]

Swan Point is that Perth?

 

[iant]

This is just an indication, its just for testing no real emergency stop circut! Its going to be a lcd with led buttons that show if you push the emergency button the led should light up so i now that the circut is right wired.

Iam not sure how to wire the inputs to the plc, like is one input one nc or? Like how many inputs is on the picture? And how to write it in ladder logic?

Thank you

This was Dome's First statement
Then he said he wanted to ship the project out

 

[duckman]

Swan Point, on the pretty little Island below you, where the reining AFL champions, the mighty "Tassie Hawks" come from.

 

[iant]

Swan Point, on the pretty little Island below you, where the reining AFL champions, the mighty "Tassie Hawks" come from.

That's that weird island south of Australia isn't it.