Safety pressure switch for process chamber utilized for coating substrate, has switch contact activated when change in e.g. form, of component part attains reference value, and evaluation device generating signal when contact is actuated

The switch has a component part (14b) e.g. snap membrane, within a housing (18), and pressure found inside a chamber (12) e.g. vacuum chamber, acts on the part, where form/shape and/or position of the component is varied according to the pressure found within the chamber. A switch contact (17b) of a micro-switch or magnetic switch, is attached to the part and is activated when the change in form/shape and/or position of the component part attains a reference value. An evaluation device generates a signal when the switching contact and another switching contact (17a) are actuated.