The PS1 consisted of a presence sensor installed on a press. In
this machine, a greasy liquid should be injected into the four ends
of the part illustrated in Fig. 2. If the operator placed any part of
his body in a hazardous area, the press would turn off automatically.
In addition, a lamp placed on the workbench would indicate,
by switching off the red light and switching on a green light, the
moment that the greasing operation had been completed, freeing
the operator to remove the piece.