Normally open, Normally closed, ladder logic

[FactoryTalktotheHand]

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?

I would at the very least use a Programmable Safety Controller as opposed to a PLC. The reason is PSCs have their own power loops for inputs (called Test Outputs). These TOs periodically drop voltage at a regular interval. Each TO on a controller does it at a different rate. When you program the controller, you specify which TO each input is reading from, and typically for an E-Stop each contact comes from a different TO.

This way, you're not only testing the E-Stop, but the entire E-Stop circuit. Without Test Outputs, you have no idea if the circuit loop is actually being closed or if someone is just applying 24vdc to it at some point, bypassing the E-Stop. It's also a way to prove that the E-Stop is indeed wired by two completely independent channels as opposed to being jumpered at the button.

I'm not sure if this would be of any help to you or not, but that is my recommendation. I've used the Omron G9SP series before which are expandable, inexpensive, and quite easy to work with.

 

[duckman]

FTH, you may have noticed l like making cynical posts, but people are still willing to offer help but Dome gave up listing/responding 4 days ago. Obviously he has more important things to do, unlike us.

 

[iant]

The best thing to do from here is to simply unsubscribe from the posts email

Dome is not interested in doing the job either safely or correctly.
Unfortunately someone will get caught and he will be nowhere to be seen

Luckily it is not here

 

[Geospark]

In addition to MartinW's sound advice...

What is being overlooked here is the fact that an Emergency Stop push-button is not a safety device. It does not fall under the Safety Related Parts of a Control System (SRPCS). It is a push button, which uses dual contacts. It is designated specific colours and markings to identify what its function is, but it is still simply a push-button. So by default, to test a push-button, alone, has nothing to do with testing safety.

However, an Emergency Stop push-button should only be used as an actuator of a Safety Function. If it is actually being used as intended, and you require testing of the Safety Function, this testing should be inherent in the Safety Function's design. The self-diagnostic tests required by a Safety Function are determined by the Safety Level required for the Safety Function i.e. Safety Integrity Level (SIL) and Performance Level (PL). (I know these standards differ somewhat for you Ian). These will usually include monitoring for loss of a single channel, cross faults and short-circuit checks, etc.

Because an Emergency Stop push-button is just a push-button, it can fail at any time. So these self-diagnostic measures of the Safety Function should ensure that the possible failures of the push-button are mitigated.

One should not be using an Emergency Stop push-button as anything other than an actuator for a Safety Function. This is its sole purpose.

So, and in short, to say one wants to test an "Emergency Stop" should only mean that you press it and it actuates its Safety Function proper, and not any method of a simulated Safety Function, such as a standard PLC and LEDs.

I would add that this goes for any situation where you choose to use an Emergency Stop push-button - from actual in use machinery, right down to a simple test station.

Unless using safety rated PLC equipment, always use a safety relay with an Emergency Stop push-button.

Regards,
George

 

[iant]

Yep I agree
I hadn't read martinw post. But spot it is spot on

I do believe the OP has moved on though.
Time for us to do the same