Yokogawa SEC401 Series Signal Converters

Technical Dossier

Product Details And Specifications

Yokogawa SEC401 Series Technical Notes

The Yokogawa SEC401 series represents a mature line of signal converters deployed extensively across global heavy industries — including petrochemical complexes, oil refinery control loops, nuclear auxiliary systems, and steel mill process instrumentation. These units serve as the critical interface layer between field transmitters and DCS/PLC control systems, converting, isolating, and conditioning analog signals (4–20 mA, 0–10 V, thermocouple, RTD) to ensure measurement integrity across long cable runs and electrically noisy environments.

Installed base for the SEC401 series spans decades of continuous operation in facilities across Asia-Pacific, the Middle East, and Europe. Their DIN-rail form factor, wide input range flexibility, and galvanic isolation characteristics made them a default specification in Yokogawa CENTUM and EJA-integrated architectures throughout the 1990s and 2000s. As of 2026, the series is in its mature/end-of-life phase — Yokogawa has transitioned newer projects to the JUXTA series — making reliable aftermarket sourcing and lifecycle support the primary procurement concern for maintenance engineers.

The Evolution of SEC401 Architecture

The SEC401 series was introduced as part of Yokogawa's signal conditioning portfolio to address the growing need for loop-powered and externally-powered isolation amplifiers in distributed control environments. Early variants (S1/S2 suffix) featured fixed input/output configurations and were designed for direct integration with Yokogawa's CENTUM CS and CENTUM CS 3000 DCS platforms.

The S3 generation — including the SEC401-11 S3 — introduced improved EMC compliance (EN 61326), extended operating temperature tolerance, and enhanced long-term drift stability. The suffix notation (e.g., -11, -21, -31) encodes the input/output signal type combination, allowing engineers to specify the exact conversion path required without additional external conditioning.

Compatibility note: SEC401 modules use standard 2-wire DIN rail terminal blocks and are interchangeable at the wiring level with many JUXTA MX series units, though firmware and calibration parameters differ. Direct substitution requires re-verification of span and zero settings. For facilities running mixed SEC401/JUXTA environments, DriveKNMS can provide cross-reference documentation and pre-configured replacement units.

SEC401 Full Catalog & Functionalities (SKU List)

The following models represent the verified active and legacy SKUs within the Yokogawa SEC401 signal converter series, organized by signal conversion function:

Current/Voltage Input → Current Output (Standard Isolation Amplifiers)

Thermocouple / RTD Input Variants

• SEC401-41 S3: Thermocouple (K/J/T/E type) input to 4–20 mA output, cold junction compensation included
• SEC401-42 S3: Thermocouple input to 0–10 V output, for voltage-input recorders and SCADA interfaces
• SEC401-51 S3: Pt100 RTD input to 4–20 mA output, 3-wire connection, linearized output
• SEC401-52 S3: Pt100 RTD input to 0–10 V output, temperature-to-voltage for panel meters

Pulse / Frequency Input Variants

• SEC401-61 S3: Pulse/frequency input to 4–20 mA output, flow totalizer interface, configurable scaling
• SEC401-62 S3: Pulse input to 0–10 V output, frequency-to-voltage conversion for speed monitoring

Potentiometer / Resistance Input Variants

• SEC401-71 S3: Potentiometer/resistance input to 4–20 mA output, position feedback signal conditioning
• SEC401-72 S3: Resistance input to 0–10 V output, valve position and actuator feedback applications

Dual-Channel / High-Density Variants

• SEC401-81 S3: Dual-channel 4–20 mA to 4–20 mA, high-density DIN rail installation, shared power supply
• SEC401-91 S3: Programmable multi-range input to 4–20 mA output, field-configurable via DIP switch

Quality Control for the SEC401 Range

Signal converters present unique verification challenges compared to passive components: a unit may power on correctly while exhibiting span drift, zero offset, or non-linearity that only manifests under load conditions. DriveKNMS applies a dedicated test protocol for all SEC401 units:

• Input simulation: Each unit is driven with a calibrated signal source (Fluke 725 or equivalent) across the full specified input range (0%, 25%, 50%, 75%, 100% of span)
• Output measurement: Output signal is measured with a precision multimeter (0.01% accuracy class) and compared against factory linearity specifications
• Isolation verification: Dielectric withstand test at 500 VDC between input, output, and power supply circuits
• Thermal soak: 4-hour burn-in at 40°C to screen for early-life component failures
• Revision verification: Hardware revision label cross-checked against Yokogawa's internal revision history to confirm S3 compliance