Two Step Start?

[geniusintraining]

How do you reset an e-stop or power failure?
james

Twist and pull and then push control ON....

 

[parky]

There are two ways I would use one for remote unattended installation & one for normal plant that is or could be attended.
There are situations where plant runs in a remote situation like a CIP plant where only engineers have access, i.e. it is normally unatended, In this situation it is generraly accepted that in the event of a power outage the plant will recover withou intervention, this situation is covered by an area that requires access via a proceedure where an access key & documentation is required usually by engineers only, there will be signs warning the plant may start automatically, will include a warning siren & beacon the plant is about to start, engineers will be trained on this system & the required lock off proceedures required.
Where plant or machinery is attended like production areas then on a stop be it power loss or operator intervention. the start will be initiated by e-stop reset & pressing a system start button. Some equipment may for example be a little remote from the controls, & possibly be attended by operators (generally not machines as they will have their own system as preceeding) but perhaps conveyors, in this case then there will be signs & warning sirens/beacons before automatic start to warn personel the system is starting. Providing the required guarding is in place in areas of possible danger on remote attended systems then that area cannot start automatically unless the guards are in place, in other words, it will require an e-stop system in it's own right but automatic re-start if the guards are closed & the main system is healthy (i.e. restarted by two stage process e-stop reset & operator automatic start).

 

[JeffKiper]

Per ISO 13849

5.2.2 Manual reset function
The following applies in addition to the requirements of Table 8.
After a stop command has been initiated by a safeguard, the stop condition shall be maintained until safe
conditions for restarting exist.
The re-establishment of the safety function by resetting of the safeguard cancels the stop command. If
indicated by the risk assessment, this cancellation of the stop command shall be confirmed by a manual,
separate and deliberate action (manual reset).

 

[JankyPLC]

Ah, yet another possible interpretation. The physical action of twisting the E-stop or closing the safety gate could be considered a step. In which case one could get the 2-step via Physical reset, then Auto Start button.

Meaning Physical reset, Reset PB, Auto Start is 3-step. Which then means Physical Reset, Reset PB, Auto/Manual Switch, Start PB is 4-step.

Obviously if your safety has EPSD that resets when the hazard is removed, like a light curtain, you lose the first step of the above.

On that note. Does anyone know of a body which will answer questions about interpretations of safety standards? For example, whats considered "Hazardous Condition" in the context of this discussion?

 

[I_Automation]

Meaning Physical reset, Reset PB, Auto Start is 3-step. Which then means Physical Reset, Reset PB, Auto/Manual Switch, Start PB is 4-step.

IF the safety relay that needs the Reset PB pressed was 'unset' or deactivated by a latching e-stop PB.


I have worked on many systems that a physical E-stop button was only 1 of a string of items in the safety relay 2 channel loop, and the other items didn't usually have a reset.


Air pressure switch, door open, low level float, laser area sensor, PLC running output, RemoteIO running output...


One set of turntable robot welders had the safety relay interrupted if there was a combination of the turntable in position OFF and the light curtain was then blocked - E-stop and no movement until reset even if the light curtain was cleared before the turntable was in a correct position.