Reset Safety zone

[aand74]

Suppose you have a safety zone with as actuators in the zone : a failsafe pneumatic pressure release valve with safety feedback, drives on profisafe and a contactor with feedback. There is an E-stop to safely shut down the installation.
There is a reset button for the safety zone.
The safety is programmed in a Siemens S7 1500 Failsafe plc.
The E-stop is in the program connected to the E-Stop failsafe function block,
The contactor and the pressure release valve are connected to the FDBACK failsafe function block that monitors feedback of respectively the contactor and the air pressure.
If the E-stopped was pressed and afterwards retracted, is it simply enough to
reset the E-Stop function block, or is it obligated to implement in the reset conditions :
- feedback contactor is off
- feedback airpressure is off
- feedback STO of drives is active

 

[aand74]

No suggestions?

 

[JTCat]

The safety E-Stop cannot be a bit that allows forcing or toggling manually. It has to be a monitored direct input that cannot be defeated.

You are describing two separate function blocks. One being an E-Stop and the next being a safety zone with it's own function block.

Are you monitoring pressures and actuator positions for unsafe conditions or just undesirable conditions and using that FB to stop the machine as well?

 

[aand74]

Let's assume :
There is
-the E-stop function block as input
-the FDBACK block that activates the contactor and checks its feedback
-the FDBACK block that activates the safety pressure valve, and that checks its feedback
- the drive on profisafe that needs the STO input to be high
All three actors need the output of the E-stop function block to be high (estop retracted and reset).
Suppose the Estop is pressed and then retracted. We reset the Estop, but the feedback of the contactor or from the safety pressure valve is active although
the Estop was not yet reset. Do we allow then that by resetting the Estop we activate the drives (STO) although the contactorfeedback of valve feedback was not off before reset? Or can any output of the safety only be activated again, if
all conditions for a safe off of the zone (in this case all feedbacks) are ok?

 

[Jim3846]

This sounds like some indetermint state where the estop was pushed and reset real fast for the ok to run conditions to be on when the estop was reset.

I thought the reset during a safety reset looks for conditons of all devices to be in a certain state before the estop can be reset. If the actuator or pressure device was not in a safe state before reset then that machine will not allow you to reset estop. This is called a failure of the estop at reset.

 

[aand74]

So, somewhere in the safety regulations is normally stated that all devices in the zone are in safe state before a reset of an estop of that zone can be done?

I thought the reset during a safety reset looks for conditons of all devices to be in a certain state before the estop can be reset.

 

[JesperMP]

I thought the reset during a safety reset looks for conditons of all devices to be in a certain state before the estop can be reset.

It depends on the chosen safety category according to EN13849-1.
Cat B and Cat 1 do not require any diagnostics.
Cat 2, 3 and 4 require diagnostics, and yes in that case you cannot reset when the devices are not in a safe state.

Because you ask like that I have to say this:
If you are dabbling with machine safety, you need to know the standards. There is a lot to it.
Do you deliver machines to customers ?
Do your company publish an EC Declaration of Conformity ?
If an accident occurs, you and your company can get into big trouble if you have delivered a machine and it is revealed that you have not followed all standards.