Desperately seeking interlocked door safety application example.

Hi all.

I am trying to find safety application examples for an inspection door with electromechanical interlock.
I can find many door switches with this function, and quite a few safety relays that alledgedly support this functionality, but I cannot find a complete solution with wiring diagram and all.

I want to know what exactly parts to use, safety relay and switch, and how to connect everything. There has got to be a complete ready-to-use application example somewhere.

The proces I have to protect is a moving part inside a machine. The part has a large rotating mass that takes a long time to run down. There is a mansized inspection door which has to be monitored.
Safety category 3.

The solution I am after is to install a switch on the door. The switch should keep the door locked until a time has elapsed after the main motor is stopped.
I prefer Siemens or Pilz. But if I cannot get a complete example from one of these two, any other vendor will get my order.

Jesper.
Guardmaster (now part of Rockwell) make a unit which seems to be exactly what you are looking for.
http://www.ab.com/safety/prod_directory/interlock_switches/guard_locking_switches/centurion_bolt-operated_mech_time_delay/index.html
regards
Andybr

Hi Andybr.

I knew that one allready. But thanks anyway
This device has a maximum delay time of 30 seconds.
My machine has a run-down time of up to 2 minutes.
It is a pity, I like the simplicity of this device.

It is not possible to install a zero motion sensor.
The only solution as I see it is a lock with an electrically controlled delay.

What's used on my current project will probably be over the top for you, but part of the idea maybe of use. We have several access points to a level 3 area, each has a castell type lock which releases a key on a signal from a Pilz safety PLC.

Attached to the castell type key is a secure registered key to the door (why they didn't have another castell type lock there I don't know). Next to this is a keyswitch and a lamp, the key for this this restricted to certain level engineers. On turning the key, the Pilz receives a signal, the Pilz then flashes the lamp to let you know its stopping the process. The Pilz sends warning signal to the equipment controller, which then issues a shutdown, after a programmable period, the Pilz drops out the supply to the drives of the equipment and releases the castell type key.

Access is then available to the equipment.

When the castell key is replaced and the request key is taken out, the Pilz re-enables power to the equipment drives.

A simple method...

http://www.castell.com/en/castell/downloads/7_1-DAE.PDF


Oops...cross-posted with PeterW

Hi Peter.

We also use a "trapped key" solution like the one you describe.
However, it is entirely mechanical. There is a mechanical timer to release the key some time after the main switch is disengaged.
It is VERY expensive, and I am not satisfied with the safety either.

Hi Krk.

I see from your link that it is exactly the make that we are using now. That green box is like a swiss clock inside.

Jesper, I am not sure exactly what you want but "I think" you want the doors to be locked until the machine is stopped..STI has components for that; http://www.sti.com/process/prosafe.htm

Hi Jesper,


These systems have been around for years (in the UK anyway), I very much doubt if Castell would be allowed to continue selling them if they weren't 100% safe & reliable...

An advantage of using a mechanical timer over the electronic timed & s.v release type systems is that you can still open the door when the machine is powered down.

Thanks Rsdoran,
but I dont want to use a trapped key solution.
I want to use a lock that stays locked until it is released from a safety relay.
I'll attach a picture:

It is from an example with a Siemens safety PLC.
I want to use a regular safety relay to achieve the safety.

In the picture there is an additional switch on the door, this to achieve safety category 4. I would like to have this extra switch even if I only need category 3.

What I want is exactly what parts should I purchase, and exactly how do I have to wire and configure everything.
I dont want to figure it out by myself.

Thanks Krk.

I have experienced two occasions where the safety was violated with the castell device:

1. The primary key could be removed from the mainswitch without the switch being disengaged. This because some brute had applied too much force in the engaged position thereby breaking a pin that insured the key from being removed.
In other words, there is no redundancy in the castell solution. A single error can violate the safety.

2. The mechanical timer had become defective and the customer had "fixed" the problem by exchanging the keying elements in the green box. In that way he could start the motor without a time delay.
The problem was that a spare green box would take too long time to send, was way too expensive for the poor customer, and so he was "forced" to tamper with the safety.
If I have an integrated solution, I can make a self-check to insure the integrity of the safety system. This is not possible with a purely mechanical solution.

Hi Jesper,

Fair points..safety systems won't keep out people who are determined to defeat them.

Is this what youre looking for then?

Jesper, see if this will work for you.
http://www.kirkkey.com/scheme34.html

Krk,

I am not 100% expert in safety systems, but I think that the Castell device can only be approved to Category 1.
To achieve higher categories there has to be redundancy and/or self-checking in the system.
Redundancy and selfchecking would have caught the problems I mentioned before.

As I cannot fit a zero motion sensor I cannot use exactly the type you have suggested. I need a timed relay, and if there is an extra doorswitch as I mentioned with my post with the picture it would be very nice.

How did you find that diagram ? It is info like that I am after.
I have tried to navigate Pilz' website, but I get lost almost immediately.

Randy,

Unfortunately the Kirkkey is another of the "trapped key" solutions. It is not what I am after.

You don't need to fit a zero motion sensor as such, just connect the PSWZ X1P unit to the motor supply and it detects motor standstill when the induced EMF =0.

S3 in the diagram is the switch/sensor for detecting the actual gate position

Krk,

I failed to see that there were 2 diagram pages. I thought that the "transponder" was a motion detector. My fault.
It looks like your suggestion is even better than my requirements because of the additional EMF detection relay.
Now I just have to find out what the price is.

Thanks.

Zero Speed

Jesper,

If I understand you correctly, what you want is a safety system in which the doors are mechanically locked shut until you have reached a zero speed state. Then they are openeable.

We have several of these systems. What you need is a safety relay, which is triggered by 2 zero speed switches. These switches should be mounted 90 degrees from one another on the axis you need to monitor. (If there is more than one, each axis gets its own ZSR). On our system, the ZSR's are then wired in series to another relay, which then tells the PLC that zero speed state has been reached, and the doors are able to be unlocked. The lock/unlock controls for the door switch coil are done in the PLC. I believe that the relays we use are guardmaster, and our locking guard switches used to be Telemechaniq, but we have recently switched the door switches to AB.

EDIT: The problem with not attaching the SZProx's directly to the mechanical shaft doing the movement and simply tying in with the motor is that the world is not a perfect place, and motor couplings can come apart. This is a big problem with high momentum applications. I would assume Jesper has one of these if he is waiting 2 minutes for standstill.


Another generic solution is to simply use a timer. This is fine, because the timer only controls the locking guard switch coil. The actual guard closed contacts are in the EStop Relay circuit, which is all safety rated.