The DO821 is an 8-channel 230V AC/DC relay normally closed (NC) output module designed for the S800 I/O within the ABB Ability™ System 800xA®. This module utilizes high-performance relay output technology and is suitable for industrial automation control systems requiring high-voltage, high-current switching control. The DO821 module features high isolation performance, reliable error detection mechanisms, and flexible system integration capabilities, making it widely applicable for equipment control and driving in fields such as power, process industries, and manufacturing.
The module supports a maximum of 250V AC voltage and 3A continuous output current, with each channel independently isolated, ensuring signal transmission stability and system safety. The DO821 is equipped with output status indicators, power supply monitoring functions, and a configurable Output Set as Predetermined (OSP) state mechanism. It can automatically set outputs to predefined safe states upon system error detection, significantly enhancing the reliability and fault tolerance of the entire control system.
Furthermore, the DO821 supports various Module Termination Units (MTUs), including compact and extended types. Users can select the appropriate MTU based on actual wiring requirements, fuse configuration, and spatial layout, enabling flexible system construction and maintenance.
Product Features and Benefits
1. High-Density Multi-Channel Output
8 independent relay output channels, each supporting 230V AC/DC loads.
Normally closed (NC) contact design, suitable for safety-first control logic.
Complete isolation between channels prevents mutual interference and enhances system stability.
2. Comprehensive Electrical Protection and Isolation
Each channel integrates an optical isolation barrier, providing electrical isolation between the control side and the field side.
Built-in EMC protection components enhance noise immunity, making it suitable for harsh industrial environments.
Insulation rating up to 250V, dielectric test voltage 2000V AC, complying with stringent industrial safety standards.
3. Real-Time Status Monitoring and Diagnostics
Each channel is equipped with an output status indicator LED, facilitating on-site debugging and fault diagnosis.
24V relay power supply monitoring function triggers an alarm signal upon power abnormality, which can be read via the ModuleBus.
Users can enable or disable power supply monitoring via a parameter, flexibly adapting to different system configurations.
4. Output Set as Predetermined (OSP) Function
Supports automatically setting outputs to a predefined state (e.g., all off or hold) upon system error detection.
OSP delay time is configurable (256ms, 512ms, 1024ms), adapting to application scenarios with different response requirements.
5. Flexible Installation and Wiring Options
Compatible with various Module Termination Units (MTUs), including:
TU811/TU813 Compact MTU: Saves space, supports two-wire connection.
TU831/TU851 Extended MTU: Provides more connection terminals and grouping options.
TU836/TU837 Extended MTU: Each channel equipped with an individual fuse (max. 3A), enhancing protection.
Supports signal return terminal grouping configuration, facilitating common ground or independent grounding designs for multiple channels.
6. High Reliability and Long Service Life
Relay mechanical life exceeds 20 million operations, electrical life exceeds 1 million operations.
Supports a maximum of 2000 switching operations per hour, meeting frequent control demands.
Low module power consumption and good heat dissipation, suitable for high-density cabinet installation.
System Integration and Installation
Compatibility Description
The DO821 module is designed for the ABB System 800xA® and S800 I/O platform, and can be seamlessly integrated with various controllers, communication modules, and host computer systems. The module communicates with the system via the ModuleBus, supporting real-time data exchange and remote parameter configuration.
MTU Selection Guide
Users can select the appropriate MTU based on wiring complexity, fuse requirements, and space constraints:
| MTU Model | Type | Key Features |
| TU811 | Compact MTU | Two-wire connection, space-saving, no individual fuses |
| TU813 | Compact MTU | Similar to TU811, suitable for simple wiring scenarios |
| TU831 | Extended MTU | Provides more connection terminals, supports grouped return terminals |
| TU836 | Extended MTU | Individual fuse per channel (3A), enhanced load-side protection |
| TU837 | Extended MTU | Individual fuse per channel, suitable for high-reliability requirements |
| TU851 | Extended MTU | Comprehensive connection and protection functions, suitable for complex systems |
Wiring Examples
Using TU831 Extended MTU: Each channel corresponds to clear positive and negative terminals. Signal returns are divided into two groups, facilitating grounding design.
Using TU811/TU813 Compact MTU: Utilizes two-wire connection, simplifying wiring, suitable for space-constrained installation environments.
Using TU836/TU837 Extended MTU: Each output channel is equipped with an individual fuse on the load side, providing overcurrent protection, suitable for critical equipment control.
Installation Notes
Ensure system power is disconnected before installation and adhere to electrical safety regulations.
Select appropriate cable cross-sections based on load characteristics and ensure reliable grounding.
The module should be installed in a cabinet meeting the required protection rating, avoiding dusty, humid, and corrosive environments.
It is recommended to configure the OSP function in conjunction with actual process safety requirements, setting appropriate delays and states.
Application Fields
The DO821 module is suitable for various industrial automation control scenarios, particularly in the following applications:
1. Power Systems
2. Process Industries
3. Manufacturing
4. Building Automation
5. Infrastructure
Selection and Ordering Information
| Item | Content |
| Product Name | DO821 Digital Output Module |
| Ordering Number | 38SE013250R1 |
| Signal Specification | 230V AC/DC (5–250V), 3A |
| Number of Channels | 8 |
| Output Type | Relay (NC) |
| Compatible Systems | ABB Ability™ System 800xA®, S800 I/O |
| Warranty & Certifications | Complies with international industrial standards such as CE, UL; standard warranty service provided |
After-Sales Service and Technical Support
ABB provides comprehensive technical support and after-sales services, including:
Free provision of product manuals, wiring diagrams, and configuration guides.
Professional technical team provides selection consultation and system integration support.
On-site commissioning and fault diagnosis services.
Regular training courses to help users gain in-depth product application knowledge.
