US Patent 7401685 Elevator testing system

The invention concerns a method and a system for ensuring the operation of the safety circuit of an elevator or escalator, said safety circuit containing safety contacts (10, 12, 14) connected in series with a contactor (16). In the method, the largest bypass current coming to the contactor in a fault situation is defined, a testing device (202) is connected in series with the safety circuit, said testing device containing at least one resistor (26), which is used to produce a desired test current that is larger than the largest bypass current, and the neutral point (18) of the safety circuit is shifted if the contactor (16) remains energized by the aforesaid test current.