The AO820 is a high-performance, highly reliable Four-Channel Galvanically Isolated Bipolar Analog Output Module, part of the ABB Ability™ System 800xA® hardware family. Designed for precise analog signal output in industrial automation and control systems, it is suitable for various process control applications requiring high-accuracy current or voltage output signals.
Each channel of the module supports bipolar current or voltage output. Users can flexibly configure the output type and range for each channel via software according to actual application needs. All channels are fully galvanically isolated from each other and from the system common, effectively preventing signal crosstalk and ground loop interference, thereby enhancing system immunity and safety.
The AO820 integrates comprehensive diagnostic and monitoring functions, including module status indication, channel open-circuit detection, output readback verification, and process power supply supervision. It features the Output Set to Predetermined state (OSP) function, which can automatically set outputs to a predefined safe state upon detection of a system error, significantly improving system availability and safety.
With a compact design, the module can be mounted on various Module Termination Units (MTUs), supporting flexible field wiring. It is suitable for diverse industrial environments such as oil & gas, power generation, metals, and water treatment.
2. Core Product Features
Four Flexible Output Channels: Each channel can be independently configured for one of the following ranges:
Current Output: -20 mA…+20 mA, 0…20 mA, 4…20 mA
Voltage Output: -10 V…+10 V, 0…10 V, 2…10 V
Full Channel Galvanic Isolation: Channels are isolated from each other and from the circuit common. Rated insulation voltage is 50 V, dielectric test voltage is 500 V AC.
Integrated Diagnostics & Safety Functions:
Front plate LED status indicators (Fault, Run, Warning, OSP).
Module-level diagnostics: Output power low.
Channel-level diagnostics: Open-circuit detection (for set output current > 1 mA).
Output Set to Predetermined state (OSP): Sets outputs to a predefined safe value within 256, 512, or 1024 ms upon detection of communication failure or module error.
Output data readback verification ensures output accuracy.
High Accuracy & Fast Response:
Resolution: 12 bits (including sign).
High Accuracy: Voltage output max. error 0.1%; Current output typical error 0.1% at 250 Ω load, max. 0.15%.
Fast Response: Rise time < 0.7 ms; Update cycle time for all channels ≤ 1.5 ms.
Robust Load Capability & Protection:
Current Output Load: ≤ 550 Ω (nominal range), ≤ 510 Ω (over-range).
Voltage Output Load: ≥ 5 kΩ.
Short-circuit proof with current limited output.
Broad Environmental Compatibility:
Operating Temperature: 0 to +55 °C (approved range: +5 to +55 °C).
Storage Temperature: -40 to +70 °C.
Protection Class: IP20.
Compliant with multiple international certifications including CE, cULus (Class 1 Division 2 / Zone 2), ATEX Zone 2, and major marine certifications (ABS, BV, DNV, LR).
3. Functional Details
3.1 Flexible Output Configuration
The core strength of the AO820 lies in its highly flexible output configuration. All four channels are completely independent, allowing users to individually select the desired current or voltage output type and range for each channel in the configuration software. Whether bidirectional control signals like ±20 mA / ±10 V or industrial standard unidirectional signals like 4…20 mA or 0…10 V are required, this module fully supports them. Separate wiring terminals are provided for current and voltage outputs in hardware; users simply need to wire correctly according to the configuration.
3.2 Comprehensive Galvanic Isolation
The module employs advanced isolation technology to achieve:
Channel-to-Channel Isolation: A fault or interference on any one channel does not affect the normal operation of other channels.
Channel-to-Ground Isolation: All channels are isolated from the ModuleBus and system common, effectively suppressing common-mode interference and improving reliability in harsh electrical environments.
This design is particularly important for sites with complex grounding systems or significant ground potential differences.
3.3 Robust Diagnostics & Safety Mechanism (OSP)
The AO820 features multi-level diagnostic functions:
Real-time Communication Supervision: Output data to the Digital-to-Analog Converters (D/A) is read back and verified to ensure output commands are executed correctly.
Continuous Open-Circuit Diagnostics: In current output mode, the module continuously monitors the output loop. A channel open-circuit error is reported when the set value requires an output > 1 mA but the actual detected current is abnormal.
Process Power Supply Supervision: Monitors the external power supply for the output loop. If this power is lost, the module generates a channel error signal.
Output Set to Predetermined state (OSP): This is a critical safety function. When the module detects communication failure with the superior controller, an internal severe error, or the diagnostic problems mentioned above, the OSP function can be activated. The module will force all channel outputs to switch to a predefined safe value (e.g., 0 mA, 4 mA, 0 V, etc.) configured in the engineering within a configurable time (256, 512, or 1024 ms), preventing controlled equipment from entering a dangerous state due to signal loss or abnormality.
3.4 High Accuracy & Dynamic Performance
With its 12-bit high resolution and precise circuit design, the AO820 delivers exceptionally accurate and stable analog outputs. Its maximum error is as low as 0.1% FS for voltage output, and a mere 0.1% for current output under typical industrial load conditions. Simultaneously, the fast rise time of less than 0.7 ms and an update cycle time not exceeding 1.5 ms for all channels ensure the system's responsiveness to rapidly changing control commands, making it suitable for closed-loop control applications requiring high dynamic performance.
4. Structure & Connection
4.1 Module Termination Unit (MTU) Compatibility
The AO820 module itself does not connect directly to field cables; it must be mounted on a Module Termination Unit (MTU). It is compatible with several MTUs, offering users different wiring options:
TU830/TU833 (Extended MTU): Provides screw terminals for direct wiring, requiring no additional terminal blocks.
TU810/TU814 (Compact MTU): Provides screw terminals in a compact form factor.
TU812 (Compact MTU): Provides a 25-pin D-Sub (male) connector, suitable for applications requiring prefabricated cables or quick connection/disconnection.
4.2 Wiring Guidelines
Separate Terminals: Each channel (Ch1-Ch4) has separate "Current Output +/-" and "Voltage Output +/-" terminals.
Key Principle: Each channel can use either the current output OR the voltage output at any one time, but never both simultaneously for the same channel. Wiring must be selected according to the software configuration.
Load Matching: Current outputs must connect to a load ≤550Ω; voltage outputs must connect to a load ≥5kΩ to ensure output accuracy and stability.
Shielding & Grounding: For the D-Sub connected TU812, its Pin 13 is connected to the connector shell for shield (EM) connection, aiding Electromagnetic Compatibility (EMC).
5. Application Areas
Thanks to its high accuracy, reliability, strong interference immunity, and comprehensive safety features, the AO820 Analog Output Module is widely used in the following fields:
Process Industries: Controlling actuators such as control valves, variable frequency drives, and proportional pumps in oil & gas, chemical, and pharmaceutical industries.
Power & Energy: Controlling steam turbine guide vanes, boiler feedwater regulation, etc., in power plants.
Manufacturing: Controlling analog servo drives for large injection molding machines, presses, and machine tools.
Water & Wastewater: Controlling pump speeds, chemical dosing pump rates, valve openings, etc.
Marine & Offshore: Compliant with major marine classification society standards, suitable for ship automation systems.
