Triconex 3805H Analog Output Module | 8-Point TMR (3805H)

Product Overview

The 3805H (3805H) is a high-availability Triple Modular Redundant (TMR) Analog Output Module engineered for the Triconex safety-instrumented system. This 8-point module provides precise 4-20 mA control signals for critical final control elements such as governor valves, dampers, and variable speed drives. Primarily deployed in the hydrocarbon processing, power generation, and specialized mining industries, the Triconex 3805H utilizes a 2-out-of-3 (2oo3) hardware voting architecture to ensure that no single point of failure can lead to an unsafe process state or an unwanted shutdown. By delivering high-accuracy loop control even during internal hardware discrepancies, the 3805H is a fundamental component in reducing Mean Time To Repair (MTTR) and maximizing overall plant production efficiency.

Advanced TMR Control Architecture

The 3805H operates through a sophisticated hardware-implemented fault tolerance (HIFT) strategy that sets it apart from standard industrial controllers.

• Triple Redundant Output Path: Each of the 8 output channels is driven by three independent sub-circuits (Leg A, B, and C). The three signals are voted upon at the hardware level within the module before being sent to the field terminal.

• 12-bit Resolution Accuracy: The module features a high-performance DAC system providing 12 bits of resolution, ensuring smooth and granular control of proportional valves and actuators.

• Continuous Loop Monitoring: The 3805H performs "loop-back" checks, where each leg monitors the actual current flowing in the output loop. If one leg detects a deviation from the commanded value, the system flags a fault while the remaining two legs maintain precise control.

• DC Coupled Current Loop: The DC coupled design ensures high signal integrity and rapid response times, essential for high-speed surge control or turbine governor applications.

Technical Specifications

Technical FAQs

How does the 3805H maintain control if one internal leg fails?

The module uses a patented voting mechanism. If one of the three internal legs fails, the hardware voter automatically ignores the faulted leg and continues to drive the 4-20 mA signal based on the remaining two healthy legs. This happens instantaneously without process interruption.

What is the significance of the 6 percent overrange capability?

The 3805H can drive signals up to 21.2 mA. This allows for specialized valve positioning and diagnostics where the controller needs to push the actuator slightly beyond the standard 20 mA limit for full-stroke verification or clearing sticktion.

Is the 3805H compatible with HART communication?

Standard 3805H modules focus on high-speed TMR safety control. If HART pass-through is required for asset management, ensure you are utilizing the correct External Termination Panel (ETP) and that the system firmware supports HART multiplexing.

Engineering & Installation Guide

• Loop Resistance Management: Ensure the total loop resistance (including field wiring and the actuator impedance) does not exceed the module's driving capability. A typical limit for the 3805H is 600 ohms at 20 mA. Exceeding this can cause the module to report a "Field Loop Fault" despite healthy internal hardware.

• Shielding and Grounding: Use high-quality shielded twisted-pair cables. Ground the shield at the Triconex chassis end only. This prevents ground loops from interfering with the 12-bit resolution and maintains the specified accuracy of < 0.25 percent.

• Thermal Consideration: In high-density cabinets, maintain vertical airflow. While the 3805H is rated for 0 to 60 deg C, prolonged operation at the upper thermal limit can reduce the lifespan of the output capacitors. Ensure cabinet fan trays are monitored.

Operational Durability & Compatibility

• Extreme Environment Performance: The 3805H is built to withstand the rigorous vibration and thermal cycling common in turbine halls and offshore platforms. The internal PCB is treated to resist corrosion in high-humidity atmospheres.

• Backward Compatibility: This module is designed to integrate seamlessly with various versions of the Tricon chassis (v9 and v10), allowing for phased upgrades of aging safety systems without the need for a total infrastructure overhaul.

• Redundant Power Feed: The module draws power from dual-redundant power rails on the backplane, ensuring that a single power supply failure within the chassis will not result in a loss of analog output control.