Elevator protection against short circuit of safety devices

An automatic elevator system having an elevator car with a car door, means for mounting said car in a hoistway extending between a plurality of floors in a building, a floor door at each one of said floors for providing access to said car, control means including hoistway apparatus for moving said car from one of said plurality of floors to another one of said plurality of floors and for stopping said car at a particular one of said plurality of floors, door operating means for automatically opening and closing said car door when the elevator car is disposed at a particular one of said plurality of floors, a plurality of switches disposed on the car and upon each one of the plurality of floors which are serially connected to each other and which, when all of the doors are closed and locked, permit operation of circuits in the control means which cause the car to move, wherein included in such plurality of switches, is a switch, located at each floor and controlled in accordance with the position of the car door and operated by the locking mechanisms which hold the doors closed until the locking mechanisms are automatically released when the car is located at a floor, each one of said plurality of switches having a first end and a second end, said first ends of said plurality of switches being connected to an electrical power supply through a point A terminal, further comprising:

• an elevator safety circuit bypass detector having two ends, one end of said elevator safety circuit bypass detector being connected to the second end of each one of said plurality of switches and the second end of said elevator safety circuit bypass detector being connected to a point B terminal which is connected to said elevator car;
• said safety circuit bypass detector having a switching device RX with a normally open contact RX1 and a normally closed contact RX2, a switching device RZ with a normally open contact RZ1 and a normally open contact RZ2;
• wherein, in normal operation when said plurality of switches are operated in a closed position, switching device RX is energized causing closing of the normally open contact RX1 and opening of the normally closed contact RX2, and switching device RZ is prevented from being energized since normally open contact RZ1 and normally closed contact RX2 are in their open state, whereby an electrical signal can be transmitted to said elevator car so as to move said elevator car;
• and
• wherein in the event that at least one of said plurality of serially connected switches malfunctions, switching devices RX and RZ are disposed in off states causing contacts RX1 and RZ1 to be in open states, whereby a signal is not transferred from said point B terminal to said elevator car, contact RZ2 in this event is disposed in its open state, and thus, said control means does not receive a signal from a terminal SX such that said elevator car is not moved.