ABB AO845A 8-Channel HART Analog Output Module

Description

3. Key Technical Specifications

The AO845A is designed for both single and redundant S800 I/O applications, providing eight isolated 4–20 mA analog outputs with built-in diagnostics and HART pass-through capability.

4. Product Introduction

The ABB AO845A is an 8-channel analog output module in the ABB S800 I/O family for AC 800M and ABB Ability™ System 800xA automation platforms. It converts digital controller commands into precise 4–20 mA analog output signals for process control devices such as control valves, I/P converters, and variable-speed drives.

Compared with standard analog output modules, the AO845A adds HART pass-through communication, supports redundant controller architectures, and continuously monitors output integrity through built-in diagnostics, making it well suited for critical process industries including power generation, chemical processing, oil & gas, and pharmaceuticals.

AO845A

AO845A

5. Installation & Configuration Guide

Stage 1 – Pre-Installation Preparation (10 Minutes)

⚠️ Safety First

1. Notify plant operations of the planned maintenance.
2. Place the process in a safe operating state.
3. Perform Lock-Out/Tag-Out (LOTO).
4. Remove cabinet power.
5. Wait at least five minutes before handling equipment.

Required Tools

• ESD wrist strap
• PH1 screwdriver
• Digital multimeter
• Wire markers
• Smartphone for documentation

Backup

• Save the Control Builder project.
• Record output channel assignments.
• Photograph all wiring.
• Document HART device configuration if applicable.

Stage 2 – Removing the Existing Module

1. Label every field cable.
2. Disconnect the terminal unit.
3. Unlock the retaining clip.
4. Pull the module straight from the ModuleBus.
5. Inspect connectors for contamination or bent contacts.

⚠️ Keep the original module until commissioning has been completed successfully.

Stage 3 – Installing the New AO845A

1. Wear an ESD wrist strap.
2. Verify the model number AO845A (3BSE045584R1).
3. Confirm the MTU is compatible (TU810, TU812, TU814, TU830, TU833, TU842, TU843, or TU852).
4. Insert the module until fully locked.
5. Reconnect all field wiring.
6. Verify terminal tightening torque.

Installation Checklist

• ✔ Correct model
• ✔ Compatible MTU
• ✔ Wiring verified
• ✔ Module locked
• ✔ Grounding confirmed

Stage 4 – Power-Up & Commissioning

Before energizing:

• Measure the 24 VDC supply.
• Check loop continuity.

Commissioning steps:

1. Energize the S800 rack.
2. Verify RUN LED status.
3. Confirm ModuleBus communication.
4. Verify HART communication where applicable.
5. Simulate 4 mA, 12 mA, and 20 mA outputs.
6. Verify field device response.

⚠️ Troubleshooting

Fault LED ON

Possible causes:

• ModuleBus communication failure
• Internal module diagnostics fault
• Output transistor fault
• Incorrect redundancy configuration

Low Output Current

Check:

• Loop resistance (≤750 Ω)
• Process power supply
• Open field wiring
• HART device configuration

The AO845A continuously monitors open circuits, short circuits, watchdog status, and internal power supply conditions, reporting faults directly to the controller.

6. Frequently Asked Questions (FAQ)

Q1. What is the primary advantage of the AO845A over the AO801?

The AO845A is intended for higher-availability applications. It supports controller redundancy, includes HART pass-through communication, and provides more comprehensive diagnostic functions than the AO801.

Q2. Does the AO845A support HART communication?

Yes. Each output channel supports HART pass-through, allowing compatible HART field devices to communicate with asset management software while maintaining the standard 4–20 mA control signal.

Q3. Can the AO845A be used in redundant S800 I/O systems?

Yes. The module is specifically designed for both single and redundant S800 I/O installations, making it suitable for applications where high system availability is required.

Q4. Which MTUs are compatible with the AO845A?

Supported MTUs include TU810V1, TU812V1, TU814V1, TU830V1, TU833, TU842, TU843, and TU852. Always verify the MTU installed in your cabinet before ordering a replacement.

Q5. Is the AO845A still available?

Yes. The AO845A remains available through industrial automation spare-parts suppliers as New Original (New Surplus) and professionally tested refurbished inventory. Availability depends on regional stock.

Q6. What output diagnostics are built into the AO845A?

The module monitors open circuits, short circuits, output transistor failures, watchdog status, checksum errors, internal power supply conditions, and process power loss, helping maintenance personnel identify field wiring or hardware faults quickly.