Do you put E-stops and guards into the alarm list?

russg

Member
Join Date
Aug 2012
Location
UK
Posts
275
Hi,

I'm just debating this with myself. I see some put it down as a warning and some down as an alarm.

I can see most times it won't be a normal "fault", but there is a chance it could be if we get a wiring or switch / guard issue.

What is the standard way, if there is one?

Thanks.
 
I always put it down as an alarm for 2 reasons


1 It shows on the alarm window


2 It stops the machine, as happens when any alarm is triggered
 
Great, thanks.

That's kind of what I'm thinking too.

A warning to me is something that doesn't usually stop the machine, for example: reel low on a wrapping machine.
 
I added E-stop alarms to the alarm screen on our machines. It was requested by management since we had cases where an E-stop was intermittent, stopped the line, and then cleared so nothing was showing on the screen. They can display the alarm log and see which E-stop was triggered.



Mike
 
I added E-stop alarms to the alarm screen on our machines. It was requested by management since we had cases where an E-stop was intermittent, stopped the line, and then cleared so nothing was showing on the screen. They can display the alarm log and see which E-stop was triggered.



Mike

Yes, I was thinking this too.

I'm also programming in a Stop Code for each module, which will be sent up to the MES system. This detects the first alarm that stopped the machine. It would seem silly not to record any estops or guards that have done this, and like you mention it could be a fault.

Thanks
 
Definitely, Especially if there are a lot of areas or possibly remote.
It can be difficult if there is no indication of E-Stop pressed maintenance can have difficulty.
One suggestion I would give is if there are a number of E-Stops or Guard switches use a spare contact back to the PLC as an alarm, also one off each safety relay, the reason is that an E-stop being pressed may not signal back to the PLC the fault due to a broken wire or bad contact etc. at least if the safety circuits show an error it is easier to determine that it is a fault somewhere on the safety system. As for a warning or alarm, generally I would say alarm, however you could write the code in such a way that if the safety circuit was ok but a guard switch or E-stop showed an error then this would be a warning i.e. the system safety is ok but there is a fault on the feedback of one of the safety devices. on the other hand, if the safety had tripped and a signal lost from a safety device showed an error, then this is an alarm.
SAFETY OK AND NO FEEDBACK = WARNING for that E-stop or Guard
SAFETY TRIPPED AND NO FEEDBACK = ALARM FOR THAT E-Stop or Guard
SAFETY TRIPPED AND FEEDBACK = General Safety Alarm, no details
It will depend on how far you will go to try and display the fault.
 
Aye, we try to ensure that the E-stop performs its primary function, but also a second signal to a PLC to indicate that the E-stop has been pushed or is healthy.

At least then when a contractor leans on the button and says "it wisnae me that shut the plant down", we can say "aye it wis ya numpty".....
The operators need to know what caused the shutdown, so yes, get them on the alarm list.
 
I had one single-hit stamping press that the supervisor kept calling me over saying it stopped mid-cycle for no reason. I checked everything more than once when this happened and found nothing.

This machine had a palm button stand on a cord with a non-latching mushroom E-stop in the center and as I stood there every few parts the operator, that had a sizeable beer-belly, would lean forward and set his belly on the E-stop.

I asked the supervisor for some thumb tacks and tape so the next time the operator did it he felt it.

All relay controls, no PLC or HMI to show what was happening.
 
I generally use the A-B 440C PSR's in conjunction with 5380 controllers.
E-Stops are all set up dual channel with a 3rd contact on the PB for feedback.

I use screen indicators for which e-stop was pressed, without an alarm. Then I monitor all channels on the PSR and will toss up an alarm based on individual channel status.

We had a problem on a project a couple months ago where one channel on a PB had an intermittent glitch, so decided to go the individual channel route with the alarms.

If you loose a channel, which only takes a blip... I have a PSR fault indicator pop up on the screen along with which e-stop had the glitch. In order to clear the fault, you just need to cycle the button then do a reset to the 440C with the hardwired reset button. That is, if the individual channel problem is solved.
 
I had one single-hit stamping press that the supervisor kept calling me over saying it stopped mid-cycle for no reason. I checked everything more than once when this happened and found nothing.

This machine had a palm button stand on a cord with a non-latching mushroom E-stop in the center and as I stood there every few parts the operator, that had a sizeable beer-belly, would lean forward and set his belly on the E-stop.

I asked the supervisor for some thumb tacks and tape so the next time the operator did it he felt it.

All relay controls, no PLC or HMI to show what was happening.

This is why it's a good idea to have independent alarms for each estop. I've seen companies waste hours of production time trying to find the estop pressed.
 
Last edited:
This is why it's a good idea to have independent alarms for each estop. I've seen companies waste hours of production time trying to find the estop pressed.


I lost a full 12 hour shift looking for an emergency stop once... eventually on handover my colleague showed me an emergency stop that was placed at knee height.
 
Anything that stops the system from operating in a "normal" or expected manner should be indicated in some form. Motor isolators are a great (And recent example). E-Stops and Access doors on our machines are alarmed by default.
 
I lost a full 12 hour shift looking for an emergency stop once... eventually on handover my colleague showed me an emergency stop that was placed at knee height.


Some of our machines have the cable type E-stop and there has to be a certain amount of tension on the cable for the switch to be clear. That has known to cause problems in searching for the trouble spot.



Mike
 
Alarm : something that has to be reacted right away, definitely e-stop is like that.
Warning : something that should be reacted in some time, might stop the process/machine
Info : Just something that operator should know
 

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