Safety circuit contactors issue

[Corbis]

Safety Circuit Issue

Update:

New contactors ordered for the 4th time to fix the issue.

Machine manufacturer working on a safety compliant retrofit for this whole circuit.

…and also although it was not relevant to the issue, some may be wondering what is purpose of these contactors anyway, as that one single drawing did not tell the whole story?

• Series NO contacts provided 24VDC to a DIGIN card to indicate all ok with the safety relay and the contactors
• Series NO contacts provided 24VDC path from a DIGOUT card to energize a solenoid permitting machine movement, and required of course as software alone must never be regarded as a safety device
• Two contactors required to prevent a weld-in condition on a single contactor and allowing a false I/O

 

[Geospark]

...Machine manufacturer working on a safety compliant retrofit for this whole circuit...

Excellent, but I wonder how many more non compliant machines they've had, or will have, come back to bite them?

We're all subject to it. We have four machines on site since 2007 with just a single Emergency Stop safety circuit, which is fine, it's all the machines require. While they fitted a PILZ safety relay, they didn't bother with a safety contactor. They just similarly used a SIEMENS relay contactor, and only one at that. While dual redundancy is not always required, it leaves these safety functions open to a high probability of an undetectable welded main contact, which did indeed happen to one of them last year.

It was the end of the late shift, home time. The PanelView backlight had gone some time that day, so they couldn't see the stop button on the screen properly. They tried to use the Emergency Stop button, but it didn't work? When it wouldn't stop, they just turned off the panel isolator for the night, but they said it took them a minute to figure out what to do. This could have been an actual emergency situation, and a minute is a long time to be waiting on Plan B. We found the SIEMENS contactor welded in the next morning. I changed that one out for a safety contactor. I hadn't room for a second or I would have added one.

Yet we have a CE Declaration of Conformity on file for these machines. Which states that it meets the relevant standards which state that you must use safety rated devices for the safety related parts of the control system.

It's not the first, and won't be the last time I'll see this. Too many machine builders are doing this in my opinion.

Regards,
George

 

[iant]

The CE declaration is not a safety compliance requirement.

This is still 'Risk Analysis' documentation from all parties.

Often I prefer to specify all Safety component parts. and SIL/CAT level
That not only guarantees the components it also ensures availability of product here (spares)