Pepperl+Fuchs KFD2-STC4-EX1.H Transmitter Power Supply – KFD2 Series

KFD2-STC4-EX1.H: Galvanically Isolated HART-Transparent Transmitter Power Supply for Zone 0 Hazardous Environments

The Pepperl+Fuchs KFD2-STC4-EX1.H is a single-channel, DIN rail-mounted transmitter power supply engineered for 2-wire 4–20 mA field instruments installed in ATEX/IECEx Zone 0, 1, and 2 hazardous locations. Operating within the KFD2 SMART Isolator platform, this unit performs three simultaneous functions: it supplies loop power to the field transmitter, galvanically isolates the hazardous-area loop from the safe-area control system, and passes HART® digital communication bidirectionally without signal attenuation or protocol conversion. The result is a single 20 mm-wide module that replaces what would otherwise require a discrete power supply, an isolation barrier, and a HART® modem — reducing panel footprint, wiring complexity, and commissioning time in a single design decision.

In a typical process control loop, the KFD2-STC4-EX1.H sits at the boundary between the field junction box and the DCS/PLC analog input card. The module draws its operating power from the Pepperl+Fuchs Power Rail bus, eliminating per-channel power wiring and enabling hot-swap replacement without loop interruption. On the field side, it presents an intrinsically safe [Ex ia Ga] IIC interface rated for Zone 0 — the most demanding hazardous classification — while on the safe side it delivers a clean 4–20 mA replica signal with a maximum load capability of 500 Ω. HART® superimposed signals (FSK, 1200/2200 Hz) pass through the isolation barrier with full amplitude integrity, allowing asset management systems such as Emerson AMS, Honeywell FDM, or ABB Asset Vision to communicate with field devices without additional hardware.

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Technical Parameters

Hardware Logical Analysis

The KFD2-STC4-EX1.H is built around a transformer-based galvanic isolation topology rather than optical coupling. This architectural choice has measurable consequences for signal fidelity: transformer isolation maintains a flat frequency response across the HART® FSK band (1200–2200 Hz) without the nonlinear capacitance effects that degrade optocoupler-based designs at elevated temperatures. The isolation barrier sustains 1.5 kV AC between field and safe sides, tested to IEC 60079-11 intrinsic safety standards, which means the module can withstand transient overvoltages generated by inductive field wiring without compromising the safe-area control system.

On the intrinsically safe output, the module implements current-limiting and energy-storage-limiting circuits that cap the maximum available energy to levels below the ignition threshold for IIC gas groups (hydrogen, acetylene). The entity parameters — Uo, Io, Po, Co, Lo — are defined in the ATEX certificate and must be verified against the connected transmitter’s entity parameters during system design. The KFD2-STC4-EX1.H is rated for Zone 0, meaning it can power transmitters installed directly in continuously explosive atmospheres, a classification that demands the most conservative energy budgets in the IEC 60079-11 framework.

The Power Rail interface eliminates the need for individual 24 V DC wiring to each module. The backplane bus distributes supply voltage across all mounted KFD2 units through a low-impedance rail, and each module draws current through an internal fuse-protected connection. This architecture reduces wiring termination count per channel from four conductors (power + signal) to two (signal only), which in a 32-channel marshalling cabinet translates to 64 fewer terminal connections — a non-trivial reduction in installation labor and potential fault points.

EMC performance is addressed through internal filtering on both the supply and signal paths. The module meets EN 61326-1 for industrial electromagnetic environments, including immunity to conducted RF interference (10 V/m, 150 kHz–80 MHz), electrostatic discharge (4 kV contact, 8 kV air), and electrical fast transients (2 kV on power lines). The compact 20 mm housing uses a grounded metal backplane contact through the DIN rail, providing a low-impedance path for shield currents without requiring a separate ground terminal.

System Integration Benefits

• Deterministic loop current accuracy: The 4–20 mA output replicates the field transmitter signal with a maximum error of ±0.1 % of span across the full operating temperature range, ensuring that DCS analog input cards receive a signal within their calibration tolerance without additional trimming.
• Zero-overhead HART® pass-through: HART® FSK signals are coupled through the isolation barrier via a dedicated AC path, preserving signal amplitude and phase characteristics. No HART® modem or protocol gateway is required between the field device and the asset management host.
• Hot-swap capability via Power Rail: Modules can be removed and replaced under live Power Rail voltage without interrupting adjacent channels, enabling corrective maintenance during plant operation without a process shutdown.
• Integrated loop diagnostics: The onboard LED provides real-time indication of loop continuity. An open-circuit field loop (broken cable or failed transmitter) drives the LED to red and forces the safe-side output to a configurable fault state (≤ 3.6 mA or ≥ 21 mA), which DCS alarm logic can detect without additional discrete wiring.
• Reduced marshalling cabinet footprint: At 20 mm width per channel, a 32-channel marshalling section occupies 640 mm of DIN rail — approximately 40 % less than equivalent relay-based isolation solutions, freeing space for terminal blocks and cable management.
• Compatibility with standard analog input cards: The 4–20 mA output is compatible with all major DCS and PLC analog input modules (Siemens S7-300/400/1500, Rockwell ControlLogix, Honeywell C300, Yokogawa CENTUM VP, Emerson DeltaV) without signal conditioning adapters.
• Simplified zone boundary documentation: Because the KFD2-STC4-EX1.H carries both ATEX and IECEx certification, a single module type satisfies the zone boundary requirements for projects governed by European ATEX directives and international IECEx schemes, reducing the number of approved component types that must be tracked in the project safety documentation.
• Scalable multi-channel architecture: The Power Rail system supports up to 32 KFD2 modules per rail segment, with segment power supplied by a single KFD2-GUT-Ex1.D power feed module. This architecture scales linearly: adding channels requires only mounting additional modules and connecting field cables, with no changes to the power distribution wiring.

Quality Assurance & Global Logistics

Every KFD2-STC4-EX1.H unit supplied by siemensplc.com is sourced through verified distribution channels and carries the original Pepperl+Fuchs factory labeling, holographic authenticity markings, and batch traceability documentation. Units are stored in a climate-controlled warehouse in Xiamen, China, in original anti-static packaging to prevent electrostatic damage to internal circuitry during storage.

Prior to dispatch, each unit undergoes a physical inspection protocol: label integrity check against the official Pepperl+Fuchs part marking specification, housing condition assessment, seal verification, and cross-reference of the batch/lot number against available manufacturer records. Units that do not pass inspection are quarantined and not shipped.

Shipment from Xiamen is available via DHL Express, FedEx International Priority, and UPS Worldwide Expedited, with typical transit times of 3–5 business days to Europe, 4–6 business days to North America, and 2–4 business days to Southeast Asia. All shipments include a commercial invoice, packing list, certificate of origin, and — upon request — copies of the ATEX/IECEx certificates. Export classification and HS code documentation are prepared for each shipment to minimize customs clearance delays. Minimum order quantity is one unit, with no upper quantity restriction for stock items. Orders confirmed before 14:00 CST are typically dispatched the same business day.

A 12-month warranty covers manufacturing defects under normal operating conditions as defined in the Pepperl+Fuchs product datasheet. Dead-on-arrival units are replaced within 5 business days of confirmed fault documentation. Warranty claims are processed directly through [email protected] with photographic evidence and the original order reference.

Contact Information

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