The BF391 24V Isolated Failsafe Monitoring Unit (shown right) enables fire alarm I/O devices, e.g. the CAST CA730 and third-party I/O devices that may not be compatible with the PSU failure requirements of BS 7273-4 CATA, to provide compliance per this door release standard. The BF391 also detects when there are multiple loop failures to the I/O device, which specific standards may stipulate.
