This safety switch is used for MDO jogging.
1 Summary[edit | edit source]
1. Connect NORMALLY CLOSED
2. Rope is not pulled == FALSE signal ==
3. Rope is pulled == TRUE signal ==
4. Mechanical limiting block must be set so that you cannot pull more than middle position
2 Hardware Connection[edit | edit source]
It is important that both normally closed NC contacts are used.
This might be a little misleading, but it is correct.
Schmersal defines the operation of its NC contacts like this:
In middle position the NC contacts are closed. This means on the other hand that when the rope is loose or pulled beyond middle position, those contacts will be open.
This is the behaviour we need to have.
The problem here is, that this switch is originally designed as emergency stop switch, but we use it as command device (to engage jogging).
So we want to have TRUE signal, if the switch is pulled into the middle position.
If we pull the rope further out of middle position, the signal would be FALSE again.
This is prevented by a mechanical limit.
The rope and the mechanical limit (locking nuts, elongated holes,rope tightener ) have to be adjusted in a way that the switch is not activated when the rope is not being pulled.
When pulling the rope, the middle position has to be reached.
The mechanical block needs to be set so that the switch cannot be pulled beyond its middle position.
Do not use the other pair of contacts (normally open).
The mechanical limit block is not for protecting the switch against damage - it is there to make sure that position 3 is never reached.
Why shall position 3 never be reached?
Because the signal would be FALSE - and when you release the rope again it will shortly become TRUE again when going over the middle position.
3 Mechanical Setup of the system[edit | edit source]
1. Pre-tighten the rope so that it is not hanging loose, but does not activate the switch yet.
The rope tightener must be equipped with counter nuts to ensure that it will not get lose later on.
Pull the rope and check if the system is able to move freely without too much friction. If the frame and the bushing is not aligned correctyl, the "piston" will stuck.
2. Pull the rope and watch the indication window on the switch. Adjust the two stopper nuts so that you will be stopped in the middle position.
3. If the thread for the counter nuts is not long enough, you still have four elongated holes for the frame.
Shift the frame accordingly so that you do have enough thread left to set the stop correctly.
4. Troubleshooting - on site solution if the thread is still not long enough.
Refer to mechanical document "platform assembly" Dok 555423 MatNum 398680.
