The AO815 Analog Output Module is a high-performance, high-reliability industrial-grade analog signal output module within the ABB Ability™ System 800xA® hardware selection system. Designed for industrial automation and process control systems, this module provides 8 independent 4…20 mA current output channels and supports HART communication protocol pass-through functionality. It is suitable for various industrial applications requiring high-precision analog signal control.
Featuring a modular design, the AO815 module offers comprehensive self-diagnostics, excellent electrical isolation, and strong anti-interference capabilities. It is widely used in automation control systems across industries such as oil and gas, chemicals, power generation, metallurgy, and water treatment, enabling precise control of field devices like valves, actuators, and variable frequency drives.
2. Key Features and Benefits
| Feature | Description |
| Number of Channels | 8 independent output channels |
| Output Signal | 4…20 mA current signal, supports ±15% overrange |
| Electrical Isolation | 8 channels as one group, isolated from ground, effectively suppressing common-mode interference |
| Short-Circuit Protection | Outputs are protected against short circuits to ZP (0 V) or +24 V, featuring current limiting |
| HART Communication | Supports HART protocol pass-through communication, point-to-point connection only |
| Diagnostic Functions | Supports module-level and channel-level internal/external fault diagnostics, includes Output Set as Predetermined (OSP) function |
| Resolution | 12-bit, providing high-precision output |
| Load Capacity | Maximum load 750 Ω, supports long-distance cable transmission (up to 600 meters) |
| Mounting Compatibility | Compatible with various Mounting Termination Units (MTUs), such as TU810, TU812, TU814, TU830, TU833 |
3. Operating Principle and Diagnostics
The AO815 module features an integrated high-performance CPU and dedicated output circuitry, with each channel utilizing independent digital-to-analog conversion and current driving units. The module performs cyclic self-diagnostics, including:
External Channel Error: Reported when the process power supply voltage is too low, or when the output current is below the set value and the set value is >1 mA (open circuit).
Internal Channel Error: Reported when the output circuit cannot provide the correct current value.
Module Error: Includes output transistor fault, short circuit, checksum error, internal power supply fault, watchdog timeout, etc.
The module's front panel is equipped with LED status indicators (F/R/W/O) representing Fault, Run, Warning, and Output Set as Predetermined states, facilitating quick on-site troubleshooting.
4. Mounting and Wiring
The AO815 module must be used with a Mounting Termination Unit (MTU) and is compatible with the following five MTU types:
| MTU Model | Type | Wiring Method |
| TU810 / TU814 | Compact MTU | Screw terminals, direct wiring |
| TU812 | Compact MTU | D-Sub 25-pin (male) connector |
| TU830 / TU833 | Extended MTU | Screw terminals, supporting higher current and more functions |
If HART communication is used, shielded cables are mandatory, and the output filter must be enabled on the corresponding channel.
Detailed wiring diagrams and terminal assignments are provided in the product manual (Figures 68, 69, 70).
5. Application Scenarios
The AO815 is suitable for the following industrial control applications:
Process valve positioning control
Variable frequency drive speed reference
Actuator position control
Proportional regulation devices
Recorder and display instrument driving
Other devices requiring 4…20 mA analog signal output
6. System Integration and Compatibility
The AO815 module is fully integrated into the ABB System 800xA or Symphony Plus control systems. It communicates with the controller via the Modulebus and supports hot swapping (depending on the MTU type). Its keying code is DB, ensuring correct pairing with the corresponding MTU and preventing misinsertion.
7. Maintenance and Diagnostic Recommendations
Periodically verify that the output current matches the set value.
When using HART, ensure the shield is grounded at a single point to avoid ground loops.
In case of module failure, quickly identify the issue using the LED status and system diagnostic interface.
When replacing a module, ensure keying code compatibility and use the same MTU model.
8. Certifications and Standards
The AO815 complies with numerous international standards and industry certifications, including:
Electrical Safety: EN 61010-1, UL 61010-1
Explosion Protection: ATEX Zone 2, cULus Class I Division 2
Marine Certifications: BV, DNV, LR
EMC: EN 61000-6-2 / 6-4
Environmental Compliance: RoHS (EU 2011/65), WEEE (EU 2012/19)
