Traditionally E-stop circuits have either been the Mushroom push button that latches down and twist to release, or a two button setup that is a N.O. push to arm/engage in series with a N.C. E-stop push button, a control relay is picked up and the a latching contact is wired across the N.O. arming P.B.
A variation that is seen on imported R.O.C. equipment is a unit that combines both of these methods, it is a relay that has two buttons mounted to it, the start button actually pushes the armature of the relay and engages the latch contact so the relay stays in, the E-stop just cuts the power to the coil, dropping it out again.
If you want to conform to electrical code, one of the first two methods would be accepted, but the prevalent method now is to use what has been mandatory in Europe for some time and this is a Safety Relay, these can come in all kinds of configurations that allow controlled shut down with internal timers and switching combinations etc.
The bottom line is that E-stop circuits should be hardwired and not be Primarily dependant on software actions.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.