Separate elevator door chain

Abstract

Elevator door chain contacts are isolated from the safety chain in a separate circuit, thus enabling the use of a separate door chain coil for independently checking the status of the door chain itself and for enabling the remainder of the safety chain. The status of the door chain itself may be checked to make sure the doors are all closed when they should be. If it is determined the door are not all shut, the car door may be cycled open and shut in an attempt to correct a possible problem at the landing. The individual hoistway door contacts in the door chain may be checked, one at a time, while the car doors are fully opened at each particular floor to make sure that the door chain is not being incorrectly shorted, i.e., to make sure the hoistway door switch contact at the particular floor is opening when it should. A checking contact may be wired into the door chain and used to selectively open circuit the door chain to ensure that the door chain coil is not directly shorted to the power supply. Since the door chain contacts are isolated from the safety chain in a separate circuit, the length of wire and the number of connections between the AC supply and the object relay coil can be reduced in both the door chain itself and the remaining part of the safety chain.