Secure Disable Applications

Case 1: Simple Start / Stop
Case 2: Interlock to EN 954-1 Cat 2
Case 3: Fail safe interlock to EN 954-1 Cat 3
Case 4: Secure Disable used in EN 954-1 Cat 4
Case 5: Provision of braking through drive
Case 6: Elevators to EN 81-1: 1998

Case 5 – Provision of braking through the drive

The drive is capable of active braking through the motor, but this not a high-integrity function. Where braking is desirable,
such as in an emergency stop function, but the actual safety function is the removal of power from the motor, a time delay
is required between instructing the drive to stop and then disabling it.

A fail-safe time delay relay can be used for this function, such as shown in Case 5. Safety relay ranges include relay expansion units with a delay feature. In this arrangement the drive brakes as soon as the gate is opened, and is disabled securely after the delay relay de-energises.

It must be emphasised that if braking is itself a safety requirement, i.e. if the braking does not operate then there is an unacceptable risk of injury, then a fail-safe brake must be provided, such as a mechanical brake with electrical hold-off.