The Yokogawa AFS20D Duplexed Field Control Unit (FCU) is a redundant controller designed for CENTUM CS 3000 and early CENTUM VP Distributed Control Systems using the Remote I/O (RIO) architecture. Unlike the rack-mounted AFS10D, the AFS20D is supplied as a cabinet-mounted Field Control Station, integrating redundant processor modules, power distribution, and RIO communication interfaces within a dedicated control cabinet. The duplex architecture provides automatic processor switchover, ensuring continuous process control during hardware failures. Proper installation, wiring, grounding, and commissioning are essential to achieve high system availability and long-term operational reliability.

Contents

• 1. AFS20D Field Control Unit Overview
• 2. Technical Features
• 3. Typical Industrial Applications
• 4. Installation Planning
• 5. Hardware Inspection
• 6. Installation Environment
• 7. Cabinet Installation Procedure
• 8. Power Supply Connections
• 9. RIO Communication Connections
• 10. Grounding Requirements
• 11. Commissioning Procedure
• 12. Functional Testing
• 13. Preventive Maintenance
• 14. Practical Installation Case
• 15. Frequently Asked Questions

AFS20D Field Control Unit Overview

The AFS20D is a cabinet-mounted duplexed Field Control Unit designed for RIO-based Field Control Stations. Two synchronized processor modules operate in active and standby modes, providing automatic failover during controller faults. The controller communicates with Remote I/O nodes through redundant RIO buses while exchanging process data over the V net control network. The processor uses 16 MB of main memory with battery-backed retention to protect application data during temporary power interruptions.

Technical Features

• Duplexed controller architecture
• Automatic processor switchover
• 16 MB main memory
• Battery-backed memory retention
• Dual-redundant V net communication
• Dual-redundant RIO bus
• Integrated cabinet design

Typical Industrial Applications

• Oil and gas production
• Petrochemical processing
• Chemical manufacturing
• Power generation
• Water treatment facilities
• Large continuous process industries

Installation Planning

• Review system drawings.
• Verify cabinet location.
• Confirm utility power availability.
• Review RIO network topology.
• Prepare controller configuration files.

Hardware Inspection

• Verify model identification.
• Inspect processor modules.
• Check cabinet wiring.
• Inspect communication interfaces.
• Verify all accessories are present.

Installation Environment

• Maintain adequate ventilation.
• Avoid excessive humidity.
• Protect against vibration.
• Prevent dust accumulation.
• Maintain specified ambient temperature.

Cabinet Installation Procedure

1. Disconnect all incoming power.
2. Position the cabinet according to engineering drawings.
3. Anchor the cabinet securely.
4. Verify controller module installation.
5. Inspect internal cable routing.
6. Confirm mechanical stability before energizing.

Power Supply Connections

• Connect redundant power inputs.
• Verify supply voltage.
• Inspect protective breakers.
• Confirm wiring integrity.
• Verify power indicators after startup.

RIO Communication Connections

• Connect redundant RIO buses.
• Verify communication cable integrity.
• Check node addressing.
• Inspect communication connectors.
• Label all network cables.

Grounding Requirements

• Connect protective earth.
• Verify cabinet grounding.
• Maintain low grounding resistance.
• Avoid ground loops.
• Inspect grounding continuity.

Commissioning Procedure

VERIFY INSTALLATION
CONNECT POWER
VERIFY GROUNDING
CONNECT RIO NETWORK
POWER UP BOTH CONTROLLERS
VERIFY SYNCHRONIZATION
DOWNLOAD APPLICATION
VERIFY PROCESS OPERATION

Functional Testing

• Verify active controller operation.
• Confirm standby controller synchronization.
• Test automatic switchover.
• Verify RIO communication.
• Review controller diagnostics.

Preventive Maintenance

• Inspect communication wiring regularly.
• Verify redundancy status.
• Review controller diagnostics.
• Replace backup batteries according to maintenance schedules.
• Inspect cabinet ventilation systems.

Practical Installation Case

During startup of a petrochemical unit, the standby controller failed to synchronize with the active processor after power-up.

Maintenance engineers found that one redundant RIO communication cable had not been fully secured during installation.

After reconnecting the cable:

• Controller synchronization completed successfully.
• Automatic switchover testing passed.
• All Remote I/O nodes became operational.
• The control station entered stable production service.

Frequently Asked Questions

What is the AFS20D?

The AFS20D is a cabinet-mounted duplexed Field Control Unit for RIO-based CENTUM systems, providing redundant controller operation and automatic processor switchover.

Does the AFS20D support redundant communications?

Yes. The controller supports dual-redundant V net communications and dual-redundant RIO buses for high system availability.

How much memory does the controller provide?

The AFS20D provides 16 MB of main memory with battery-backed retention to preserve controller data during temporary power loss.

Summary: Proper installation of the Yokogawa AFS20D Duplexed Field Control Unit requires correct cabinet installation, redundant power wiring, reliable RIO communication, effective grounding, and comprehensive commissioning. Following these procedures ensures high controller availability, dependable redundancy, and stable long-term process control.