The ABB AO801 Analog Output Module is a key component of the ABB Ability™ System 800xA® automation system, belonging to the S800L series I/O hardware family. Designed for industrial automation control applications requiring high-precision, high-reliability analog signal output, this module provides 8 independent single-ended, unipolar analog current output channels, supporting standard 0...20 mA and 4...20 mA industrial signal formats. The AO801 module integrates advanced self-diagnostic and fault protection mechanisms, ensuring stable, continuous operation in harsh industrial environments. It is an ideal choice for precise process control in fields such as process industries, manufacturing, and energy.
As part of the ABB System 800xA distributed control system, the AO801 module integrates seamlessly with other system components. It communicates via the high-speed Modulebus and enables precise control of field actuators (e.g., control valves, variable frequency drives, motor starters). Its modular, compact design facilitates installation and maintenance, while its comprehensive safety certifications (e.g., CE, ATEX, cULus, and major marine classification societies) ensure compliance and suitability for use in various industrial and hazardous environments worldwide.
2. Key Features and Benefits
The core design of the AO801 module revolves around reliability, precision, and safety. Its main functions and advantages are demonstrated in the following aspects:
High-Performance Multi-Channel Output:
Provides 8 mutually isolated analog current output channels.
Each channel can be independently configured for 0...20 mA or 4...20 mA output. The 4...20 mA range is handled by the upper-level controller or Field Communication Interface (FCI), complying with industry standards and supporting a "live zero" signal.
Single-ended output design simplifies wiring.
Enhanced System Safety and Reliability:
Output Set as Predetermined (OSP) Function: Upon detecting an internal fault (e.g., communication loss, internal diagnostic error), the module can automatically set all output channels to a user-predefined safe state (e.g., hold last value, fall to minimum or maximum), preventing process runaways. This is a key feature for ensuring operational safety.
Comprehensive Self-Diagnostics: The module periodically performs internal self-tests, monitoring power supply, internal circuitry, and channel status. Module status, faults, and channel-level errors are reported in real-time via front-panel status LEDs and system software.
Short-Circuit Protection: The output stage is designed as a short-circuit proof and current limited type. Even if the output is accidentally shorted to zero potential (ZP) or the +24V supply, it will not cause permanent module damage, greatly enhancing system robustness.
Groupwise Isolation: All output channels are electrically isolated as a group from system ground, effectively suppressing common-mode interference and improving signal integrity and system immunity.
Excellent Dynamic Performance and Accuracy:
High Resolution: Employs a 12-bit Digital-to-Analog Converter (DAC) for fine output control.
Fast Response: Signal settling time (rise time) is typically only 10 µs, and the module update cycle is 1 ms, meeting the requirements of fast control loops.
High Accuracy and Low Temperature Drift: At 25°C, the maximum full-scale error does not exceed 0.1%. The temperature drift coefficient is typically 30 ppm/°C, with a maximum of 60 ppm/°C, ensuring stable output over a wide temperature range.
Flexible Connection and Installation:
Process signal and power supply connections use detachable terminal blocks, facilitating installation, commissioning, and maintenance.
Supports a wide range of wire sizes (Solid: 0.05-2.5 mm²; Stranded: 0.05-1.5 mm²) and provides recommended torque values (0.5-0.6 Nm) and stripping lengths (6-7.5 mm) for standardized workmanship.
The module is compact in size (W 86.1mm x D 58.5mm x H 110mm) and lightweight (0.24kg), suitable for high-density rail mounting.
Robust Environmental Compatibility:
Wide operating temperature range: 0 to +55 °C (certified for +5 to +55°C). Storage temperature range is -40 to +70 °C.
High protection rating: IP20 (protection against finger contact and solid objects ≥12.5mm diameter), meeting requirements for installation inside control cabinets.
Good humidity tolerance: Supports 5% to 95% relative humidity (non-condensing).
Comprehensive corrosion protection: Complies with ISA-571.04 G3 level, suitable for industrial environments with mildly corrosive atmospheres.
Extensive Industry Certifications:
Electromagnetic Compatibility (EMC): Complies with EN 61000-6-2 (Immunity for industrial environments) and EN 61000-6-4 (Emission for industrial environments).
Electrical Safety: Complies with EN/UL 61010-1 and EN/UL 61010-2-201.
Hazardous Area Certifications: Suitable for Class I Division 2 (cULus) and ATEX/IECEx Zone 2 hazardous areas, providing access approval for applications in oil & gas, chemical, and similar industries.
Marine Certifications: Certified by major classification societies including ABS (USA), BV (France), DNV (Norway), LR (UK), suitable for maritime applications.
Environmental Compliance: Complies with EU directives RoHS (2011/65/EU) and WEEE (2012/19/EU).
3. Design Principle and Power Dissipation Calculation
1. Module Block Diagram Overview:
The functional block diagram shows that the core of the AO801 module is a microprocessor (CPU) responsible for communicating with the superior controller via the Modulebus Interface (MBI) and managing the D/A converters for all 8 channels. Each channel's output stage is equipped with EMC protection circuitry to ensure signal quality. The module internally monitors the 5V and 24V supply status (Power_ok), which forms the basis for self-diagnostics and status indication.
2. Power Dissipation Calculation (Key Consideration):
The total module power dissipation (typically 3.8W) mainly originates from the output stages. To ensure long-term reliable module operation (maintaining high MTBF), the actual power dissipation of the output stages must be calculated to avoid overheating due to excessive load. The output stage power dissipation is calculated as follows:
When the external supply voltage for the output stages, UP, is < 24 V:
P_output = Σ [ (UP - 4.7 - (R_Li + 100) × I_CHi) × I_CHi ] (i=1 to 8)
When the external supply voltage for the output stages, UP, is ≥ 24 V:
P_output = Σ [ (19.3 - (R_Li + 100) × I_CHi) × I_CHi ] (i=1 to 8)
Where:
UP: Power supply voltage to the output stages
I_CHi: Average output current of channel i (A)
R_Li: Load resistance of channel i (Ω)
The 100 Ω in the formula represents the fixed impedance of the module's internal output loop.
Calculation Criterion: The sum of the power dissipation from all 8 channels, P_output, must be less than 1.2 W. This check is especially necessary when the output load is less than 250 ohms and a higher supply voltage is used. Short-term overload or short circuit will not damage the module, but long-term overload will significantly reduce the module's Mean Time Between Failures (MTBF).
4. Installation, Wiring, and Application
1. Terminal Assignment:
The module's 16 process terminals (10, 1-, 20, 2- … 80, 8-) correspond to the positive output and return (ZP) for each of the 8 channels respectively. Clear markings facilitate wiring and circuit checking.
2. Typical Wiring Diagram:
Each channel is connected in a 2-wire configuration to the field device (e.g., valve positioner). The module's "+ Output" terminal connects to the device's signal positive terminal, and the device's negative or common terminal connects to the corresponding "Return (ZP)" terminal on the module. This wiring represents the standard current loop connection method.
3. Application Fields:
The ABB AO801 module is widely used in scenarios requiring high-precision analog control, for example:
Process Industries: Control of flow, pressure, temperature, and level control valves in chemical, petrochemical, pharmaceutical, and water treatment plants.
Power & Energy: Boiler feedwater control, turbine speed control, fuel supply control.
Manufacturing: Production line speed control, tension control, temperature control.
Marine & Offshore: Engine control, ballast water systems, steering gear control.
Building Automation: Control of dampers and water valves in large HVAC systems.
