E-stop will not reset

Hello,

I'm having an issue on a machine where one of the E-stops won't reset from the fault screen. It does not show it is active on the PLC input screen if you have the button pressed in or pulled out, but it does show up if you press another e-stop button elsewhere on the machine. I'm having a hard time wrapping my head around this. Any suggestions?
 
It is not uncommon for a machine/system to be installed with all the Emergency Stops wired back to the PLC for ease of identification on the rare occasions when operated. Then with the best of intentions maintenance add another Emergency Stop station, wire in to the emergency stop circuit but don’t/cannot wire back to the PLC.
Perhaps this is a good time to see if changes or upgrades have been marked on factory drawings.
 
Emergency stops can sometimes be wired with 2 (or more) contacts within the emergency stop button.
1 (or 2 ) break contacts for the emergency stop circuit connected to the safety relay.
And a separate contact for signalling to the PLC.
 
Typically, the normally closed contact is used for the emergency button, If the contacts of two emergency button in different positions are connected in parallel, then you must press both of two buttons at the same time to trip the unit, by pressing any button alone will not work. You can change the connection of the contacts of these two buttons to series connection, so that you can trip the unit by pressing any button.
If you use normally open contacts, you need to connect the contacts of the two buttons in parallel.
 
It also happened to me that only 1 of the 2 safety circuits was opened en I could not re-activate the safety relay.
I first had to open -both- safety circuits and only after that I was able to reset the circuit.
This happened when I installed a photocell in one of the 2 circuits because the customer wanted something quick and cheap because he forgot something in the RIA (risk and safety assesment).
At the end we had to install the very expensive Pilz photocell system that really switched both circuits. Unfortunately for him it cost 2200 euro's per machine iso just 200 for the 1 photocell.....
 
Yes I know, I also used it in fully integrated television tube production lines with many machines running in line with different paths throughout the factory. It is a really nice system, if you know how it works.
And modbus is still my favorite fieldbus: it is so simple and you can have it up and running in just a few seconds if you have the modbus parameter list.
Its so nice and easy.
 
Hello,

I'm having an issue on a machine where one of the E-stops won't reset from the fault screen. It does not show it is active on the PLC input screen if you have the button pressed in or pulled out, but it does show up if you press another e-stop button elsewhere on the machine. I'm having a hard time wrapping my head around this. Any suggestions?
This smells like a system we were Installing / Starting up.
If only one wire is being opened (with the PB), the safety will trip, but cannot be reset.
These safety relays are continuously checking to make sure that both channels are
re-energized, AT THE SAME TIME.
If only one channel is opened, that device will have to be reset locally, and then a two
channel device will have to be tripped and reclosed before the safety relay will allow a
reset.
Designed to prevent safety tampering etc.
Both circuits need to be complete within mS of each other or you cannot reset the safety.
 
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