P+F KFD2-STC5-EX2 — Dual-Channel NAMUR Sensor Safety Barrier | Pepperl+Fuchs KFD2 Series
Engineering Background: In process industries operating with flammable gases, vapors, or combustible dust, field instruments installed in hazardous areas (Zone 0, Zone 1, Zone 2 / Div. 1 & 2) must be electrically isolated from safe-area control systems. The Zener-diode isolating barrier is the foundational technology for intrinsic safety (Ex i), limiting the energy that can enter the hazardous zone to levels incapable of igniting an explosive atmosphere — even under single-fault conditions.
Product Positioning: The Pepperl+Fuchs KFD2-STC5-EX2 is a 2-channel, DIN rail-mounted Zener safety barrier engineered for NAMUR-compatible proximity switches and binary sensors in SIL 2 safety loops. It provides galvanic separation between the hazardous-area field device and the safe-area PLC/DCS input card, while delivering the precise 8 V / 8 mA NAMUR supply required by IEC 60947-5-6 compliant sensors. Widely deployed in oil & gas, petrochemical, pharmaceutical, and power generation facilities, the KFD2-STC5-EX2 is a trusted component in functional safety architectures worldwide.
Complete Technical Specifications
| Manufacturer | Pepperl+Fuchs (P+F) |
| Part Number | KFD2-STC5-EX2 |
| Series | KFD2 — Zener Isolating Barrier |
| Function | 2-channel NAMUR sensor interface / safety barrier |
| Supply Voltage | 20–35 V DC (from KF-bus or external 24 V DC) |
| Sensor Supply | 8 V DC / 8 mA per channel (NAMUR per IEC 60947-5-6) |
| Output | Transistor output (PNP), short-circuit protected |
| Switching Threshold | Active: >2.1 mA; Inactive: <1.2 mA (NAMUR standard) |
| Channels | 2 (independent) |
| Galvanic Isolation | Yes — field / power / output fully isolated |
| Hazardous Area Classification | Ex ia IIC / IIB / IIA — Zone 0, 1, 2 (ATEX & IECEx) |
| Safe Area Classification | Zone 2 permissible |
| SIL Rating | SIL 2 (IEC 61508) |
| Mounting | DIN rail (35 mm), snap-on |
| Housing Width | 20 mm (single-width module) |
| Operating Temperature | -20 °C to +60 °C |
| Storage Temperature | -40 °C to +85 °C |
| Protection Class | IP20 |
| Weight | approx. 200 g |
| Certifications | ATEX, IECEx, cULus, FM |
| Approvals | II 2(1) G Ex ia [ia Ga] IIC T4 Gb |
| Connection | Screw terminals, max. 2.5 mm² |
| LED Indication | Green (power), Yellow per channel (output state) |
Proven Application Environments
- Oil & Gas: Wellhead proximity sensing, pipeline valve position feedback, compressor surge detection in Zone 1 areas
- Petrochemical / Refinery: Reactor level switches, pump seal monitoring, rotating equipment speed sensing
- Pharmaceutical: Clean-in-place (CIP) vessel level detection, isolator glove-box sensor interfaces
- Power Generation: Turbine blade proximity, boiler drum level, coal mill speed monitoring
- Chemical Processing: Solvent tank high-level alarms, agitator rotation confirmation, ESD valve position
- Offshore Platforms: Subsea control module interfaces, HVAC damper position in classified spaces
Engineering Advantages
- True Galvanic Isolation: Eliminates ground loops and common-mode interference — critical in large plant installations with multiple earthing points
- Dual-Channel Efficiency: Two independent NAMUR channels in a 20 mm housing reduces panel space by 50% vs. single-channel alternatives
- SIL 2 Certified: Fully characterized PFD and PFH data available for functional safety calculations per IEC 61508 / IEC 61511
- NAMUR NE 43 Compliant: Supports wire-break and short-circuit diagnostics — fault states are distinguishable from process states
- KF-Bus Power Distribution: Compatible with Pepperl+Fuchs KF-Bus power rail — eliminates individual power wiring per module
- Universal Certification: ATEX + IECEx + FM + cULus — single part number satisfies global project requirements
- Long-Term Availability: Active production status; backward-compatible with legacy KFD2 installations
System Architecture & Signal Flow
The KFD2-STC5-EX2 operates as a passive-active hybrid interface:
- Field Side (Hazardous Area): NAMUR sensor (2-wire, 8 V supply) connected to terminals 1/2 (Ch.1) and 4/5 (Ch.2). The barrier limits voltage and current to Ex ia levels via Zener diodes and series resistors.
- Isolation Stage: Transformer-based galvanic isolation provides >500 V AC reinforced insulation between field and safe-area circuits.
- Safe Side Output: PNP transistor output (terminals 14/15 Ch.1, 24/25 Ch.2) drives PLC digital input cards directly. Output current up to 100 mA.
- Power: Supplied via KF-Bus rail or terminals 16(+)/17(−) at 20–35 V DC. Power LED confirms module health.
- Diagnostics: Wire-break (<0.1 mA) and short-circuit (>6 mA) conditions drive output to defined safe state, distinguishable by NAMUR NE 43 logic in the DCS.
Sourcing & Quality Verification
- Origin: Sourced from authorized Pepperl+Fuchs distribution channels and verified industrial surplus with full traceability
- Inspection Protocol: Each unit undergoes visual inspection, label verification (date code, country of manufacture), and functional power-on test prior to dispatch
- Authenticity Markers: Genuine P+F units feature holographic certification labels, laser-etched part numbers, and tamper-evident housing seams — all verified before shipment
- Documentation: Original P+F datasheet, EU Declaration of Conformity, and ATEX certificate copies available upon request
- Packaging: Ships in anti-static bag with original or equivalent protective packaging; terminal covers included
Procurement Process
- Confirm Part Number: Verify KFD2-STC5-EX2 against your BOM or P+F product selector — confirm no suffix variants (e.g., -Y1, -Y2) are required for your application
- Request Quote: Contact [email protected] with quantity and required delivery date for volume pricing
- Lead Time: In-stock units ship within 1–3 business days; ETA confirmation provided at order placement
- Export Compliance: HS Code 8536.90 — standard industrial control component; no ECCN restrictions for most destinations
- Payment & Terms: T/T, PayPal, and trade credit available for qualified accounts; proforma invoice issued upon order confirmation
- After-Sales: 12-month warranty against manufacturing defects; technical support via email within 24 hours
Technical FAQ
Q: Can the KFD2-STC5-EX2 interface with non-NAMUR sensors (e.g., mechanical contacts)?
A: Yes. Mechanical contacts can be connected directly — the barrier interprets open contact as inactive (<1.2 mA) and closed contact as active (>2.1 mA). No additional resistor is required for standard dry contacts.
Q: Is external power required, or can it run from the KF-Bus rail alone?
A: The module is fully powered from the KF-Bus rail (24 V DC). External terminal power is only needed if the KF-Bus system is not used.
Q: What is the maximum cable length to the hazardous-area sensor?
A: Determined by the Ex ia entity parameters (Ui, Ii, Pi, Ci, Li) and the sensor’s entity parameters. Typically 300–1000 m with standard 0.5 mm² shielded cable — consult the P+F entity parameter sheet for exact calculation.
Q: Can two KFD2-STC5-EX2 channels be used for a single SIL 2 loop in 1oo2 voting?
A: Yes. The two independent channels support 1oo2 (one-out-of-two) redundant sensor architectures. Each channel must be connected to a separate DCS input for the voting logic to function correctly.
Q: Is the KFD2-STC5-EX2 compatible with the Pepperl+Fuchs FieldConnex system?
A: No — FieldConnex is a FOUNDATION Fieldbus / PROFIBUS PA infrastructure product. The KFD2-STC5-EX2 is a discrete (binary) signal barrier and is not part of the FieldConnex portfolio.
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