ABB AO845 S800 I/O Redundant Analog Output Module

The ABB AO845, also cataloged as the AO845 Analog Output Module (Article Number 3BSE023676R1), operates as a dedicated hardware component for converting digital control commands into 4-20 mA HART loops within ABB System 800xA and S800 I/O platforms. Configured for single or redundant deployment across the S800 ModuleBus, the module drives eight unipolar current channels to field actuators while executing continuous cyclic self-diagnostics. Internal power distribution splits between the +5 VDC ModuleBus logic rail and an external +24 VDC process supply.

Hardware Specifications

Deterministic ModuleBus Execution and Signal Isolation

The AO845 interface exchanges cyclic field data directly across the backplane rail, utilizing backplane bus communication velocity to process updating frames every 10 ms without lagging the main controller loop. Internal firmware flash compatibility ensures synchronized hardware handshake execution when paired with a redundant module on a extended baseplate. Galvanic groupwise isolation separates process power lines from backplane logic channels, preventing stray ground loops from corrupting the 12-bit analog signal resolution.

Frequently Asked Questions

Q: How does the AO845 module report an open circuit on an active output channel?

A: The module triggers an External Channel Error if the loop current drops below the programmed setpoint value while the requested output is greater than 1 mA, or if the process power supply voltage falls below the operating threshold.

Q: What action does the ModuleBus master take if an internal circuit fault occurs in a redundant configuration?

A: If an internal channel driver fails to deliver the commanded current output, the ModuleBus master commands the faulty AO845 module into an error state, triggering an instant failover to the active secondary module.

Q: Does the AO845 module support hot-swapping under live process conditions?

A: Yes. The AO845 module can be removed and replaced on an active ModuleBus baseplate without turning off system power or disrupting communication to adjacent I/O slots.

Field Installation Guidelines

Snap the S800 terminal baseplate onto a standard 35 mm DIN rail, verifying that the grounding spring makes solid, clean contact with the unpainted metal rail surface. Carefully seat the AO845 module onto the baseplate guide pins until the mechanical locking latches fully engage.

Route shielded 4-20 mA field cables separately from high-voltage AC lines to prevent electromagnetic interference. Connect overall cable shields to the ground bus bar using low-impedance grounding clamps. Ensure that the external +24 VDC process power supply is connected to supply adequate loop voltage across maximum 750 Ohm load impedances. Maintain at least 50 mm of vertical clearance above and below the module enclosure for proper convective airflow up to +55 deg C.