Elevator safety circuit

An elevator safety circuit for an elevator system, the elevator safety circuit comprising:

• an input arranged to receive an electrical current from a supply;
• an output arranged to selectively provide the electrical current to an electromagnetic brake coil via a current flow path;
• an actuator transistor arranged in series along the current flow path between the input and the output, said actuator transistor having an enabled mode in which it allows passage of the electrical current, and a disabled mode in which it interrupts the current flow path thereby preventing passage of the electrical current;
• and
• a controller arranged to carry out a test operation when the braking element is in the open position, wherein the test operation comprises operating the actuator transistor in its disabled mode for a time period, monitoring the electrical current through the brake coil, and determining whether the magnitude of the electrical current reduces during said time period;
• wherein the time period is selected such that the magnitude of the electrical current remains greater than the threshold current during said time period.

A method of testing a brake in an elevator system, wherein:

• the brake includes a braking element and an electromagnetic brake coil, said brake being arranged to pass an electrical current from a supply to the brake coil via a current flow path, said brake being arranged to apply a mechanical bias force to operate the braking element in a closed position when a magnitude of the electrical current is less than a threshold value, wherein the electromagnetic coil produces an electromagnetic force that overcomes said bias force to operate the braking element in an open position when the electrical current is equal to or greater than the threshold value;
• and
• an actuator transistor is arranged in series along the current flow path between the supply and the brake coil, said actuator transistor having an enabled mode in which it allows passage of the electrical current, and a disabled mode in which it interrupts the current flow path thereby preventing passage of the electrical current;
• the method comprising:
• when the braking element is in the open position, operating the actuator transistor in its disabled mode for a time period;
• monitoring the electrical current through the brake coil;
• and
• determining whether the magnitude of the electrical current reduces during said time period;
• wherein the time period is selected such that the magnitude of the electrical current remains greater than the threshold current during said time period.