Triconex 3805H High-Density Analog Output Module

Functional Overview

The Triconex 3805H serves as a high-performance analog output interface for the Tricon High-Availability Controller platform. This module actively utilizes Triple Modular Redundancy (TMR) architecture to provide reliable, continuous signals to modulating field devices. By integrating three independent output sub-circuits that share a common output point, the unit ensures that control loops—such as those for turbine speed or control valve positioning—remain stable and accurate even if a hardware fault occurs within one of the redundant paths.

TMR Signal Integrity and Precision

The 3805H is engineered to deliver high-precision 4-20 mA signals while maintaining complete fault tolerance. It achieves this through a sophisticated internal voting mechanism:

• Triple Redundancy: Three separate microprocessors independently calculate the output value and drive three internal analog stages.
• Output Voting: A patented hardware-based current-summing architecture “votes” on the final output, ensuring the field signal remains correct even if one internal channel deviates.
• Resolution: Provides 12-bit resolution to ensure smooth and precise control of proportional actuators and variable frequency drives.
• High Density: Features 8 isolated analog output channels, allowing for the management of multiple control loops from a single module slot.

Diagnostics and Self-Testing Capabilities

To comply with SIL 3 safety requirements, the 3805H performs extensive background self-tests without interrupting the output signal. These active diagnostic features include:

• Loop-Back Monitoring: The module continuously senses the actual output current and compares it against the commanded value to detect discrepancies.
• Field Power Supervision: Actively monitors the external 24 V DC field power supply and triggers an alarm if the voltage falls below operational thresholds.
• Hot-Spare Support: Supports the installation of a redundant “Hot-Spare” module in an adjacent slot, enabling 100% availability during module replacement or maintenance.
• Fault Indicators: The front panel includes “Pass,” “Fault,” and “Active” LEDs for the module, along with individual status indicators for each of the 8 channels.

Application and Safety Compliance

Because of its “H” (High-Density/High-Performance) designation and TMR reliability, the 3805H is the preferred choice for mission-critical modulating control. It is extensively used in the following areas:

• Turbomachinery Control: Managing fuel valves and steam governors for high-speed turbines.
• Critical Process Loops: Controlling pressure and flow regulators in chemical reactors and oil refineries.
• Nuclear I&C: Safety-related analog control in power generation facilities.
• Emergency Venting: Coordinating the precise opening of relief valves in safety-instrumented systems (SIS).

Technical Specifications

• Number of Outputs: 8 Channels (Isolated)
• Output Signal Range: 4 to 20 mA DC
• Accuracy: < 0.25% of FSR (Full Scale Range) from 0 to 60 °C
• Safety Rating: SIL 3 certified (IEC 61508)
• Output Loop Power: External 24 V DC nominal
• Operating Temperature: 0 °C to 60 °C (32 °F to 140 °F)
• Module Type: TMR High-Density Analog Output