KFD2-STC4-Ex2 Pepperl+Fuchs SMART Transmitter Power Supply Barrier

Engineering Overview: High-Precision Signal Isolation

The KFD2-STC4-Ex2 by Pepperl+Fuchs is a dual-channel, galvanically isolated barrier specifically engineered for the reliable power supply and signal processing of 2-wire SMART transmitters. This module serves as a critical interface between field instrumentation and control systems, ensuring precise 0/4–20 mA loop transmission while maintaining stringent intrinsic safety standards. With a bandwidth reaching 7.5 kHz and a settling time of 200 µs, the KFD2-STC4-Ex2 ensures rapid, transparent communication for HART-compatible field devices.

Performance & Technical Specifications

• Model: KFD2-STC4-Ex2
• Channels: 2-channel isolated barrier
• Supply Voltage: 20 to 35 V DC
• Input Signal: 0/4 to 20 mA (for 2-wire SMART transmitters)
• Output Signal: 0/4 to 20 mA
• Load Impedance: 0 to 550 Ω @ 20 mA
• Accuracy: ≤ 10 µA (incl. calibration and linearity)
• Temperature Drift: 0.25 µA/K
• Mounting: 35 mm DIN rail (EN 60715)
• Safety Integrity: SIL 2 per IEC/EN 61508
• Dimensions: 20 x 124 x 115 mm (housing type B2)

Global PLC Spare HUB’s Insight

The KFD2-STC4-Ex2 is a workhorse in hazardous area instrumentation. Unlike general-purpose isolators, this unit is perfectly tuned for the bidirectional digital communication required by HART protocols. In our experience, this module is the go-to solution for petrochemical and offshore applications where reliable diagnostic loop data is as critical as the process variable itself. Its compact B2 housing allows for high-density DIN rail packing without sacrificing thermal dissipation.

Hazardous Area Approvals & Diagnostics

• Intrinsic Safety: [Ex ia Ga] IIC, [Ex ia Da] IIIC, [Ex ia Ma] I
• Hazardous Ratings: ATEX, IECEx, and UL/cULus approved for explosive atmospheres.
• Diagnostic Capabilities: Integrated LED status indicators provide immediate visual confirmation of channel health. The design includes front-access test points, allowing technicians to verify loop current without breaking the field wiring—a critical feature for proactive maintenance in live systems.

Logistics, Warranty, and Support

• Shipping: Expedited global transit via FedEx, UPS, and DHL.
• Turnaround: Orders dispatched within 24–48 hours.
• Warranty: Professional 12-month quality assurance guarantee.

Expert Frequently Asked Questions

How does the 200 µs settling time impact my control loop performance?
The rapid settling time ensures minimal phase lag in your control signal, which is essential for high-speed PID loops where even minor delays could induce oscillations in process variables.

Can I use this barrier with non-SMART transmitters?
Yes, the unit is fully backward compatible with standard 2-wire 4–20 mA transmitters, though it is optimized specifically to pass the digital overlays used by SMART devices.

Is the 16 V minimum available voltage sufficient for my sensor?
For most standard SMART transmitters, 16 V at 20 mA provides ample power to maintain operation even with significant cable resistance, but verify your transmitter's minimum startup voltage during the design phase.

What is the best way to leverage the front test points for troubleshooting?
Connect a high-impedance multimeter to the test points to measure the loop current during commissioning. This allows you to calibrate the PLC input without having to disconnect the transmitter and lose your safety interlocks.

How does the Ex nA rating influence my cabinet design?
This rating allows the barrier to be installed in Division 2/Zone 2 non-hazardous enclosures while the field wiring extends into Division 1/Zone 0 hazardous areas, greatly simplifying total installation complexity.

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