Yokogawa SEC401 Series Signal Converters

Technical Dossier

Product Details And Specifications

Yokogawa SEC401 Series: Comprehensive Module Range and Technical Overview

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)

• SEC401-11 S3: 4–20 mA input to 4–20 mA output, 2-port isolation, DIN rail mount, S3 revision
• SEC401-11 S2: 4–20 mA to 4–20 mA, earlier S2 revision, fixed span, legacy stock only
• SEC401-12 S3: 4–20 mA input to 0–10 V output, galvanic isolation, loop-powered compatible
• SEC401-21 S3: 0–10 V input to 4–20 mA output, voltage-to-current conversion with isolation
• SEC401-22 S3: 0–10 V input to 0–10 V output, voltage repeater with 3-port isolation
• SEC401-31 S3: 0–5 V input to 4–20 mA output, low-voltage signal conditioning for legacy sensors
• SEC401-32 S3: 0–5 V input to 0–10 V output, signal range expansion with isolation barrier

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

Sourcing Hard-to-Find & Obsolete SEC401 Parts

With Yokogawa having officially transitioned the SEC401 series to end-of-active-production status, procurement teams face three distinct supply chain risks: (1) authorized distributor stock depletion, (2) counterfeit units entering the gray market, and (3) undocumented hardware revisions in surplus stock that may not meet original calibration specifications.

DriveKNMS maintains a dedicated inventory tracking system for SEC401 series units sourced from decommissioned plant equipment, authorized surplus channels, and verified OEM overstock. Every unit undergoes physical inspection and signal path verification before shipment. For S2-revision units specifically — which are no longer available through any authorized channel — we maintain a documented chain of custody and can provide calibration certificates traceable to original Yokogawa factory specifications.

For procurement managers running lifecycle extension programs on CENTUM CS 3000 or older DCS architectures, we recommend establishing a standing blanket order for SEC401 critical spares. Lead times for verified stock: 3–7 business days for standard models; 10–21 business days for rare variants. Emergency same-day dispatch available for stocked units via DHL Express.

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

Units that fail any test parameter are quarantined and not offered for sale. Test records are retained for 3 years and available to customers upon request.