DO821 ABB S800 I/O Relay Output Module DO821 | Buy Online

Product Overview

The ABB DO821 (Article Number: 3BSE013250R1) is an 8-channel relay normal closed (NC) digital output module designed for the S800 I/O process automation platform. Operating across 5 to 250 V a.c./d.c. field voltages with a continuous current rating of 3 A per channel, each output features complete channel-to-channel optical isolation. The DO821 integrates Output Set Predetermined (OSP) fail-safe handling, ModuleBus relay power supervision, individual channel LED indicators, and robust EMC suppression components for high-reliability switching in DCS environments.

Technical Specifications (MECE Framework)

1. Basic System Identification

• Manufacturer: ABB
• Model / Order Code: DO821 / 3BSE013250R1
• Product Series: S800 I/O System
• Module Type: Normally Closed (NC) Relay Digital Output Module
• Mechanical Keying Code: CA

2. Channel Electrical & Signal Characteristics

3. Environment, Standards & Base Compatibility

• Operating Temperature: 0 to +55 °C (+32 to +131 °F) horizontal; capped at +40 °C (+104 °F) for vertical compact mounting.
• Conformal Coating / Environment: Corrosion protection ISA-S71.04: G3 compliant; Pollution Degree 2; IP20 protection.
• Marine Certifications: Approved by ABS, Bureau Veritas (BV), Det Norske Veritas (DNV), and Lloyd's Register (LR).
• Electrical Safety Compliance: EN 61010-1, UL 61010-1, EN 61010-2-201, and UL 61010-2-201.
• Compatible Module Termination Units (MTUs): TU811, TU811V1, TU813, TU831, TU836, TU837, and TU851.

4. Physical Dimensions & Weight

• Dimensions: 45 mm Width x 119 mm Height x 102 mm Depth (111 mm depth including rear connector).
• Unit Net Weight: 0.23 kg (0.5 lbs).

System Diagnostics & Hardware Self-Monitoring

The DO821 module contains comprehensive diagnostic hardware for continuous operational oversight. The front panel features 12 status LEDs: Fault (F), Run (R), Warning (W), Output Set Predetermined (O), and status lights for Channels 1 through 8. An internal converter monitor checks the 24V supply derived from the ModuleBus. If internal supply levels drop, a hardware error flag is sent via ModuleBus, triggering the Warning LED and logging module error tables inside the System 800xA or AC800M controller.

Target Machinery & Application Scenarios

• Fail-safe shutdown circuits requiring Normally Closed (NC) contact logic to drop out power on signal loss.
• Interfacing high-voltage 230 VAC interlocks and motor starter coil control circuits.
• Emergency alarm annunciation, relay isolation barriers, and power distribution switching.
• Harsh chemical or offshore environments requiring ISA-S71.04 G3 corrosion resistance and marine approvals.

Installation & Wiring Guidelines

Snap the DO821 onto a compatible MTU base (e.g., TU811V1) with ModuleBus power removed. Align mechanical keying wheel CA to match the MTU socket setting. Ensure maximum continuous current per channel does not exceed 3 A, and select appropriate external fusing at the MTU terminals if field line short-circuit protection is required. Maintain clearance above and below the module base to facilitate convective air circulation when switching inductive 230 VAC loads.

Packaging, Logistics & Warranty Terms

• Package Scope: 1x Factory Sealed ABB DO821 S800 Output Module (3BSE013250R1), Installation Manual.
• Warranty Terms: Full 12-month comprehensive warranty against mechanical and electronic defects.
• Dispatch Processing: Rapid warehouse handling with 24 to 48 hour shipping execution.
• Global Carriers: Expedited global door-to-door transit via FedEx, UPS, or DHL.

Global PLC Spare HUB's Insight & Field Experience

During a control retrofitting project on a marine vessel, our engineers investigated a false trip warning flagged on an DO821 module. Diagnostic telemetry indicated intermittent 24V supply error messages over the ModuleBus, even though output loads operated normally. Investigation revealed high electrical ripple on the primary power bus caused by an aging power supply unit. Replacing the ModuleBus power line filtering stabilized voltage levels and cleared the internal supervision warning instantly. Field Tip: When utilizing NC relay outputs for critical fail-safe circuits, verify that external suppressors (RC snubbers) are fitted across AC contactor coils to eliminate inductive arc feedback into the relay contacts.

Selection & Buyer's Guide

Before purchasing the DO821, ensure your system logic explicitly requires Normally Closed (NC) contact states rather than Normally Open (NO) outputs (such as DO820). Confirm that your mounting orientation allows sufficient thermal headroom: while horizontal installation supports up to 55 °C ambient environments, vertical mounting inside compact MTUs limits the maximum ambient rating to 40 °C to preserve internal relay contact life.

Frequently Asked Questions (FAQ)

Q1: What contact behavior should be expected from the DO821 outputs when system power is completely removed?

A: Because channels are Normally Closed (NC), contacts remain physically closed in an unpowered state, making it ideal for fail-safe de-energize-to-trip loops.

Q2: Can the internal ModuleBus relay supply supervision feature be disabled during commissioning?

A: Yes, software parameter settings within the controller engineering tool allow engineers to enable or disable 24/12 V relay power monitoring flags as needed.

Q3: How does the Output Set Predetermined (OSP) function protect processes during bus loss?

A: If ModuleBus communication fails, the module automatically forces the 8 output channels into user-preconfigured fail-safe contact states.

Q4: Is external field power required to drive the internal relay coils of the module?

A: No external auxiliary power supply is required; internal relay driving voltage is derived directly from the +24 V ModuleBus distribution lines.

Q5: What mechanical precautions prevent installing this module into an incorrect MTU socket?

A: The module uses mechanical keying code CA, which must match the adjustable keying dial on the MTU base to allow proper physical mating.

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