Honeywell KCD2-SCD-EX1 KCD2-STC-EX1 Safety Barrier – KCD2 Series

Honeywell KCD2-SCD-EX1 / KCD2-STC-EX1 — Galvanically Isolated SMART Transmitter Power Supply for Hazardous-Area Control Loops

In process automation architectures where field instruments reside in IEC 60079-classified hazardous zones, the signal conditioning barrier occupies a structurally critical position: it is the sole electrical interface between an energy-limited intrinsically safe circuit and the unrestricted safe-area control system. The Honeywell KCD2-SCD-EX1 and KCD2-STC-EX1 are single-channel, DIN-rail mounted, galvanically isolated transmitter power supply modules engineered to fulfill this role for 2-wire 4–20 mA / HART field devices. Both models belong to the KCD2 Series — Honeywell’s compact, high-density family of certified safety barriers — and are deployed across oil & gas, chemical, pharmaceutical, and power generation facilities where ATEX and IECEx compliance is a baseline engineering requirement, not an option.

The distinction between the two part numbers lies in their output-side termination and signal routing configuration. The KCD2-SCD-EX1 provides a single-channel output with standard screw-terminal connectivity suited for direct DCS/PLC analog input wiring. The KCD2-STC-EX1 incorporates an integrated termination concept compatible with the KCD2 bus system, enabling centralized 24 V DC supply distribution across multiple barrier modules without individual field wiring to each unit’s supply terminals. Both variants maintain identical hazardous-area electrical parameters and carry the same Ex ia IIC certification envelope.

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Technical Parameters

Hardware Logical Analysis

The KCD2-SCD-EX1 and KCD2-STC-EX1 implement a three-port galvanic isolation topology using transformer-based DC/DC conversion on the power path and optocoupler-based signal transfer on the analog current loop. This architecture is architecturally distinct from Zener barrier designs: whereas a Zener barrier relies on shunt diodes and series resistors to clamp hazardous-area energy below ignition thresholds — and in doing so introduces a fixed voltage drop and a mandatory earth bonding requirement — the KCD2 galvanic isolator imposes no earth bonding constraint and introduces negligible loop resistance on the field side, preserving the full compliance voltage headroom for the connected transmitter.

The intrinsic safety parameters (Ui, Ii, Pi, Ci, Li) are defined at the field-side terminals and are certified to remain below the ignition energy thresholds for Gas Group IIC (hydrogen reference gas) — the most demanding classification in the IEC 60079-11 framework. This means the same module can be deployed in hydrogen, acetylene, and carbon disulfide atmospheres without re-certification, providing engineering flexibility across diverse process chemistries.

EMC performance is achieved through a combination of internal shielding between the transformer windings, common-mode choke filtering on the supply input, and transient voltage suppression (TVS) diodes at the safe-area output terminals. The result is a common-mode rejection ratio (CMRR) sufficient to suppress ground-loop interference in installations where the DCS analog input card and the field transmitter share different earth reference potentials — a common condition in large-scale plant wiring where cable runs exceed 500 m.

The HART signal path is handled by a dedicated high-impedance AC coupling network that extracts the FSK-modulated HART carrier (1200 Hz / 2200 Hz, ±0.5 mA superimposed on the 4–20 mA DC loop) without disturbing the DC operating point of the transmitter. The coupling network presents a load impedance of ≥ 230 Ω to the HART master, satisfying the minimum load requirement specified in the HART Communication Foundation physical layer standard. This ensures compatibility with all HART revision levels (5, 6, 7) and with both point-to-point and multi-drop wiring configurations.

System Integration Benefits

• Zero earth bonding requirement: Galvanic isolation eliminates the mandatory safety earth connection required by Zener barriers, simplifying cabinet design and reducing installation labor in facilities with poor earth quality.
• Full HART protocol transparency: The AC-coupled HART path passes all HART commands (universal, common practice, device-specific) without modification, enabling remote configuration, loop diagnostics, and predictive maintenance via any HART-compatible asset management system (AMS, PACTware, FieldCare).
• High-density cabinet layout: The 12.5 mm module width allows 64 channels per 800 mm DIN rail segment, reducing marshalling cabinet footprint by up to 40 % compared to 22.5 mm-wide barrier formats.
• Universal DCS/PLC compatibility: The 4–20 mA output interfaces directly with analog input cards from Siemens (S7-300/400/1500, PCS 7), ABB (800xA), Emerson (DeltaV), Yokogawa (CENTUM VP), and Rockwell Automation (ControlLogix) without signal conversion.
• KCD2 bus system integration (KCD2-STC-EX1): The STC variant connects to the KCD2 power bus rail, distributing 24 V DC to all modules on the rail from a single supply connection — eliminating per-module supply wiring and reducing terminal block count.
• Deterministic loop response: The analog signal path introduces a propagation delay of < 5 ms, well within the scan cycle requirements of modern DCS controllers operating at 100–500 ms loop execution rates, ensuring no measurable contribution to control loop dead time.
• Diagnostic transparency: HART Device Status byte and Extended Device Status are passed unmodified to the HART master, allowing the DCS to surface field device diagnostics (sensor degradation, process alerts, configuration warnings) without additional hardware.
• Long-term spare parts availability: The KCD2 platform has been in continuous production for over two decades. Honeywell maintains backward compatibility across KCD2 module generations, protecting the capital investment in existing marshalling infrastructure.

Quality Assurance & Global Logistics

Every KCD2-SCD-EX1 and KCD2-STC-EX1 unit supplied by siemensplc.com is sourced through verified distribution channels carrying full Honeywell factory traceability. Authenticity verification includes cross-referencing the module’s date code, certification label typography, and holographic markings against Honeywell’s current production standards. Units are stored in ESD-controlled, temperature-regulated warehouse conditions in Xiamen, China, maintaining the factory-specified storage environment throughout the holding period.

Export documentation — including commercial invoice, packing list, certificate of origin, and manufacturer certificate of conformity (available on request) — is prepared in compliance with Chinese customs regulations and the import requirements of the destination country. Shipments are dispatched via DHL Express, FedEx International Priority, and UPS Worldwide Expedited, with typical transit times of 3–7 business days to Europe, North America, Southeast Asia, and the Middle East. For project quantities requiring freight consolidation, FCL/LCL sea freight and air freight via IATA-certified forwarders are available. All shipments are fully insured and tracked from dispatch to delivery confirmation.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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