Gaurding Question

Gentlemen

I am having a difference of opinion with the mechanical guys (surprise). When a gaurd is opened, requiring a reset, does the resart of the machine require a separate action to restart?

Thanks

yes.

I would advise not to do an automatic restart.

Reset the "fault (guard off/open)" - one action.
Restart the machine - second action.

good practice.......

Totally agree, 20 year old machines, doing refits, and I am hearing "that is the way it has always been"

Just wish I could find a rule concerning this, good practice to give the operator a second to think yes I want to restart it.

Good practice doesnt cut it with these guys

Machine guarding is part of an emergency stop circuit.

If not, it should be....

To quote from this forum:

http://www.plctalk.net/qanda/showthread.php?t=82037


"6.2.5.2.2 Effects of emergency stop and reset commands
Once active operation of the emergency stop device has ceased following an emergency stop command,the effect of this command shall be sustained until the device is reset. This reset shall be possible only at
that location where the emergency stop command has been initiated. The reset of the command shall not restart the machinery but shall only permit restarting."

This excerpt is from CSA Z432-04, safeguarding of machinery. "

JohnCalderwood said:

Machine guarding is part of an emergency stop circuit.

If not, it should be....

To quote from this forum:

http://www.plctalk.net/qanda/showthread.php?t=82037


"6.2.5.2.2 Effects of emergency stop and reset commands
Once active operation of the emergency stop device has ceased following an emergency stop command,the effect of this command shall be sustained until the device is reset. This reset shall be possible only at
that location where the emergency stop command has been initiated. The reset of the command shall not restart the machinery but shall only permit restarting."

This excerpt is from CSA Z432-04, safeguarding of machinery. "

Click to expand...

Good and practical information but we do not necessarily follow the CSA directive here in the States.
The OP should have the US equivalent to be most effective at his location.

But then in his location I hear that pretty much anything goes.

We do not follow that in Scotland either, even though I work for a Canadian company, hence I included the link to the forum thread, where USA replies appear to be the most frequent....

Originally posted by timothymajka:

...I am hearing "that is the way it has always been"

Click to expand...

That'll look good on somebody's tombstone.

Having an automatic cycle restart on a guard reset is probably not the best idea. However, only you or whoever at your site evaluates hazards can really make that determination based on the hazards involved.

Keith

I do automatic restart on the safety system, only if there is no chance of another person being exposed to the hazard. I always make the restart of the machine function manual.


ISO 13849-1:2006(E)
5.2.3 Start/restart function
The following applies in addition to the requirements of Table 8.
A restart shall take place automatically only if a hazardous situation cannot exist. In particular, for interlocking guards with a start function, ISO 12100-2:2003, 5.3.2.5, applies.
These requirements for start and restart shall also apply to machines which can be controlled remotely.

NOTE A sensor feedback signal to the control system can initiate an automatic restart.

EXAMPLE In automatic machine operations, sensor feedback signals to the control system are often used to control
the process flow. If a work piece has come out of position, the process flow is stopped. If the monitoring of the interlocked safeguard is not superior to the automatic process control, there could be a danger of restarting the machine while the operator readjusts the work piece. Therefore the remotely controlled restart ought not to be allowed until the safeguard is closed again and the maintainer has left the hazardous area. The contribution of prevention of unexpected start-up provided by the control system is dependant on the result of the risk assessment.

kamenges said:

That'll look good on somebody's tombstone.

Click to expand...

I think "But that's how we've always done it" is the suit and tie version of "Hold my beer and watch this"

OP, I feel your pain... Once upon a time I worked at a plant that had a controls team and an Electrical Lead. Back in those days an Engineer could just ask his boss. Seems like the days are gone when you can just ask someone who knows as much or more about controls than the engineer on the project.... Or are we just working at the wrong places?

Please reference pdf pages 47 and 48 of the linked document.

https://downloads.omron.eu/IAB/Logi..._Catalog_2015_2016_EN_Y25IE03_201503_FULL.pdf

First column on page 47 references the standards.

Auto/Manual Reset section column 2 provides explanation.

Tried to attach just the two pages, but exceeds attachment limit.

Hope this helps.