Desperately seeking interlocked door safety application example.

[JesperMP]

Thankyou both of you.

I have gone through both these vendors sites, and missed both of them. It just goes to show that it is a bit hard to find stuff. I may have taken the wrong route by going to the application examples 1st and then take the safety relays mentioned in the examples as the ones I would have to use.

I need up to 120 seconds delay, so I cannot use the STI SR223SMT device.

About the PILZ e1vp 300, I can see that there are many possibilities, but I have failed to figure out how to connect it up - my failure I am sure. Why isnt there a complete application example ?

I will continue to look into the matter. Any inputs are still welcome

 

[JesperMP]

Back again with the interlocked door.

Hello again.

After much digging I have found several example of such a safety combination with a door that is locked for an extended time.
One example from Siemens shows that the coil to the lock is applied voltage to lock the door.
Another example from Sick shows that the coil to the lock is applied voltage to release the door.

1. I knew that both versions exist, but when would/shall you choose one over the other ?

2. I think that the safest is to apply voltage to release the door. But that means that you need a safety relay with delayed activation. It appears that Siemens do not have such a safety relay, whereas Sick do have. Are there others ?

Thanks.

 

[jstolaruk]

But that means that you need a safety relay with delayed activation..

There are several relays with delayed normally closed outputs; PILZ, AB, Jocab, etc. But that is for the condition that you want to automaticaly unlock the door if the safety relay kicks off. Or you could use a normally closed contact n a safety contactor that is controlled by a safety relay.

But consider this scenario: we use the activate-to-release door switches to control when the operator is allowed into a hazardous area. The operator presses a button indicating to the PLC that he wants to access the interior of the cell. The PLC finishes the current cycle and then moves to a maintenance or home position. Once accomplished the PLC uses a non-hazardous output to activate the unlock mechanism allowing the operator to open the door. When the door opens the safety relay trips and kills all hazardous motion. This method is preferred by many of our customers to implement category 2 shutdown of servo equipment OR if these is vertical movement that requires to be rod-locked or shotpinned into a specific position to disallow a crush/pinch condition.

 

[drawson]

This is actually a pretty simple application.

Combine a pair of locking door switches like the ones here

http://www.bannerengineering.com/products/subfam.php?subi_id=40

With a dual channel safety module with time delay such as the one here:

http://www.bannerengineering.com/products/subfam.php?subi_id=584

Wire a pair of normally closed (such that the contacts are closed when the disconect is open and motor is de-energized) auxiliary contacts from your spindle motor disconnect into the safety module.

This will ensure that the door switches stay locked and entry is controlled until the preset timer expires after the machine has been locked out.

 

[drawson]

One more fine point. If you truly need a category 3 safety rated system then you can't use most PLCs as a control element in the safety circuit. There are some lines of safety rated controllers out there such as a Guardlogix by Rockwell but that is way overkill for this application.

 

[jstolaruk]

One more fine point. If you truly need a category 3 safety rated system then you can't use most PLCs as a control element in the safety circuit. There are some lines of safety rated controllers out there such as a Guardlogix by Rockwell but that is way overkill for this application.

You are definitely correct. Just a note, my example described a PLC unlocking a gate solenoid. It is not part of the safety circuit nor was it intended to be. All it was doing was allowing when the operator could open the gate and tripping the safety circuit. A PLC can also be used to reset a safety relay and still satisfy all categories. Basically, any element that can be performed by the operator with respect to unlock or reset, a PLC can be supplemented. Once a harm sitution becomes exposed, the regular PLC better be out of the circuit.

The Guardlogix is unbelieveably expensive. I did get the chance to implement a safety PLC made by Jokab on a small conveyor control. It replaced the PLC and the safety relay and its cost was 75% of the individual items.

 

[JesperMP]

Thankyou both.

For most of the examples I have seen, the locking of the door is a part of the safety circuit. This to achieve class 4/SIL3. Normally the lock is unlocked by the safety circuit + the lock itself is monitored. You can put the PLC in the unlock circuit.

I have spoken to a PILZ expert and he say that in most cases a safety PLC or a programmable safety relay is used for thsis kind of application.
We are considering to use a safety PLC (Siemens F range, not so expensive actually), but for now we want to just do the door with regular safety relays.

The example from PILZ uses a regular PNOZ6 relay + a PZA timer unit.
I really would like to get complete application examples from several vendors. It worries me that there are so few examples, and the ones that I can find are so different from each other.

 

[PLC Pie Guy]

Hey there.
I want to start by saying I realize this is an old thread. I am curious however what the outcome was . I have a similar situation where I need to lock a door based on the EMF from a motor. JasperMP, did you ever find a suitable solution to this problem?
It seems not a lot of solutions exist for this kind of issue.

Thanks

 

[JesperMP]

The outcome was that the existing system with a Castell trapped-key box with mechanical delay timer was retained.

One thing that works against the electrically delayed lock is that to achieve Performance Level PLd or PLe, 2 contactors redundantly in series are needed (rather than just 1 start contactor). That becomes quite a significant extra cost when the machine is big. We have up to 1000 kW in the biggest configuration.

 

[PLC Pie Guy]

Thanks for the info.
I may look into something similar.

Cheers!