In an industrial application, this would require "two hand anti-tie down", that is, both switches must turn off between operations/cycles or the next operation/cycle cannot occur. Without this, the operator has no way of knowing if one switch or button has already failed (or intentionally is held) "on" and it is only a matter of time before the second fails, causing unexpected machine operation. Manufacturers such as Pilz and Allen-Bradley sell certified Two-Hand Control Safety Relays designed specifically for this purpose, or you could build one yourself with three relays and the proper design.
How interesting they make relays to achieve that. I can sure see how for everyday use with some dangerous piece of industrial equipment. that next level of safety would be well worth it.
Yes - just use NC (normally closed) switch that you have to keep pressing to keep open/off. For a two hand version like this you would put both switches in parallel so if one lets go of either, it triggers. I'm guessing you want to attach it to an alarm of some kind?
I have heard a story that a woman got a limb cut off using a machine that had a dead mans switch. The machine had 2 switches that you had to press for the machine to start its cycle. The voltage used going through the switches is 230 volts. And the switches are of course in series so both had to be pressed. But when she was working in the machine the machine started a cycle on its own. The investigation showed that it must have been the voltage spikes that always are on the grid was the cause. The switches was probably simple 230 volts switches and could maybe withstand one or two thousand volts in open state. But the grid can have up to 6000 volt spikes on it. So the high voltage spike triggered the machine. Then we can use 24 volts also. But then there is another thing one must take care of. The 0V on the 24 volt side must be grounded. Otherwise two faults could bypass the switches without the fuse blowing. For example 24 v somehow connects to ground and then the last switch one side also connects to ground and machine starts. If 0V was grounded the fuse for the 24V would have tripped when the first fault occurred. I have some ideas heating up cables that you can do in your videos. I hope to get into contact with you.
This sounds like a case of lack of lockout/tagout. If working inside the machine all hazardous energy sources must be locked out and tagged to prevent operation.
@@soundspark I may have had bad wording when I said "working in the machine". I ment the usual work that operator does when exchanging part to be processed, like every 5-10 seconds, like stamping a sheet metal into a cup or something. The machine safety relied on two switches not being pressed (at the same time) while hands where in the machine. But lets say they had invented lockout at that time and it was implemented it would probably be based on same flawed security by using same type of switches but just putting a lock on them. The 6000 volt would still pass the switches.
@@Jonas_Aa In an industrial application, this would require "two hand anti-tie down", that is, both switches must turn off between operations/cycles or the next operation/cycle cannot occur. Without this, the operator has no way of knowing if one switch or button has already failed (or intentionally is held) "on" and it is only a matter of time before the second fails, causing unexpected machine operation. Manufacturers such as Pilz and Allen-Bradley sell certified Two-Hand Control Safety Relays designed specifically for this purpose, or you could build one yourself with three relays and the proper design.
@@danwoodson2384 This was a long time ago before the knowledge. I usually use the safety relays from Phoenix. There are still people out there thinking an input pin to a regular software is an emergency stop.
In an industrial application, this would require "two hand anti-tie down", that is, both switches must turn off between operations/cycles or the next operation/cycle cannot occur. Without this, the operator has no way of knowing if one switch or button has already failed (or intentionally is held) "on" and it is only a matter of time before the second fails, causing unexpected machine operation. Manufacturers such as Pilz and Allen-Bradley sell certified Two-Hand Control Safety Relays designed specifically for this purpose, or you could build one yourself with three relays and the proper design.
How interesting they make relays to achieve that. I can sure see how for everyday use with some dangerous piece of industrial equipment. that next level of safety would be well worth it.
Is there a way to set up a reverse sleeping man switch, so something turns ON when you fall asleep?
Yes - just use NC (normally closed) switch that you have to keep pressing to keep open/off. For a two hand version like this you would put both switches in parallel so if one lets go of either, it triggers. I'm guessing you want to attach it to an alarm of some kind?
I have heard a story that a woman got a limb cut off using a machine that had a dead mans switch.
The machine had 2 switches that you had to press for the machine to start its cycle. The voltage used going through the switches is 230 volts. And the switches are of course in series so both had to be pressed.
But when she was working in the machine the machine started a cycle on its own. The investigation showed that it must have been the voltage spikes that always are on the grid was the cause. The switches was probably simple 230 volts switches and could maybe withstand one or two thousand volts in open state. But the grid can have up to 6000 volt spikes on it. So the high voltage spike triggered the machine.
Then we can use 24 volts also. But then there is another thing one must take care of. The 0V on the 24 volt side must be grounded. Otherwise two faults could bypass the switches without the fuse blowing. For example 24 v somehow connects to ground and then the last switch one side also connects to ground and machine starts. If 0V was grounded the fuse for the 24V would have tripped when the first fault occurred.
I have some ideas heating up cables that you can do in your videos. I hope to get into contact with you.
This sounds like a case of lack of lockout/tagout. If working inside the machine all hazardous energy sources must be locked out and tagged to prevent operation.
@@soundspark I may have had bad wording when I said "working in the machine". I ment the usual work that operator does when exchanging part to be processed, like every 5-10 seconds, like stamping a sheet metal into a cup or something. The machine safety relied on two switches not being pressed (at the same time) while hands where in the machine.
But lets say they had invented lockout at that time and it was implemented it would probably be based on same flawed security by using same type of switches but just putting a lock on them. The 6000 volt would still pass the switches.
@@Jonas_Aa In an industrial application, this would require "two hand anti-tie down", that is, both switches must turn off between operations/cycles or the next operation/cycle cannot occur. Without this, the operator has no way of knowing if one switch or button has already failed (or intentionally is held) "on" and it is only a matter of time before the second fails, causing unexpected machine operation. Manufacturers such as Pilz and Allen-Bradley sell certified Two-Hand Control Safety Relays designed specifically for this purpose, or you could build one yourself with three relays and the proper design.
@@danwoodson2384 This was a long time ago before the knowledge.
I usually use the safety relays from Phoenix.
There are still people out there thinking an input pin to a regular software is an emergency stop.