Emerson Rosemount 975 Series, Reference Manual

Page: 26 / 44

The detector can be set to perform the BIT in the following modes:
• Automatically and manually
• Manually only
BIT operation
The BIT is intended to check optical integrity and electronic circuitry. The detector's status
remains unchanged if the result of a BIT is the same as the current status (Normal or BIT
Fault). The detector’s status changes if the BIT differs from the current status.
Note
In BIT Fault status, the detector can continue to detect a fire in most cases.
Automatic BIT
The detector automatically performs a BIT every 15 minutes. A successful BIT sequence
does not activate any indicator. If required, you can modify the automatic BIT interval
using the RS-485 Modbus
®
Manager or HART
®
communicator. In case of a BIT fault, this
sequence continues until a successful BIT occurs, when the detector resumes normal
operation.
• As the result of a successful automatic/manual BIT, the fault relay remains energized .
• As the result of an unsuccessful automatic/manual BIT (which occurs after three
failures), the fault relay de-energizes .
Manual BIT
You can initiate manual BIT using the Modbus Manager or HART communicator or by
connecting terminal
3 to ground. You can also use the Modbus Manager or HART
communicator to configure the manual BIT's alarm duration.
Initial setup Reference Manual
February 2022 00809-1400-4975
26 Emerson.com/Rosemount