PEPPERL+FUCHS KFD2-STC4-1 | Smart Transmitter Isolator 4-20mA
PEPPERL+FUCHS KFD2-STC4-1 | Smart Transmitter Isolator 4-20mA - Image 2
PEPPERL+FUCHS KFD2-STC4-1 | Smart Transmitter Isolator 4-20mA - Image 3

PEPPERL+FUCHS KFD2-STC4-1 | Smart Transmitter Isolator 4-20mA

  • Model: KFD2-STC4-1 (also referenced as KFD2-STC4-Ex1)
  • Brand: PEPPERL+FUCHS (P+F)
  • Series: K-System
  • Core Function: 1-channel isolated barrier for smart transmitters
  • Type: Analog Input Signal Conditioner / Safety Barrier
  • Key Specs: 4-20mA input/output, SIL 3 functional safety, HART transparent
Category: SKU: PEPPERL+FUCHS KFD2-STC4-1

Description

Key Technical Specifications

  • Signal Type: Analog input (Smart Transmitter)
  • Input Signal: 0/4 … 20 mA (field side)
  • Output Signal: 0/4 … 20 mA (control side, overload > 25 mA)
  • Power Supply: 20 … 35 V DC (Power Rail or terminals 14+, 15-)
  • Power Consumption: 2.4 W (typical)
  • Load: 0 … 550 Ω at 20 mA
  • Safety Integrity Level: SIL 3 (according to IEC 61508)
  • Bandwidth: 0 … 7.5 kHz (-3 dB)
  • Settling Time: 200 µs
  • Ambient Temperature: -20 … 60°C (-4 … 140°F)
  • Degree of Protection: IP20
  • Galvanic Isolation: Output/Power supply (50 V AC rated insulation)

Product Introduction

The PEPPERL+FUCHS KFD2-STC4-1 is a 1-channel isolated barrier designed to power and transmit analog signals from smart transmitters in hazardous areas to the safe area. It supports standard 2-wire and 3-wire transmitters and is fully transparent to superimposed digital communication protocols like HART, BRAIN, or Foxboro.Engineered for high-reliability process automation, this isolator achieves SIL 3 safety standards, making it suitable for critical safety loops. It features a fast settling time of 200 µs and a bandwidth of up to 7.5 kHz, ensuring precise signal transmission without lag. The unit is powered via a 24VDC supply rail or standard terminals, simplifying cabinet wiring.

 

Installation & Configuration Guide

Phase 1: Preparation (10 min)

  • Verify the model number (KFD2-STC4-1) on the side label matches your control system requirements.
  • Ensure you have a 20-35VDC power supply ready. If using a P+F power rail, confirm the backplane bus is energized.
  • Gather a small flat-head screwdriver for the terminal blocks.

Phase 2: Removal (If replacing)

  • Power down the cabinet or isolate the 24VDC supply to the K-System rack.
  • Use a flat-head screwdriver to gently pry the bottom and top clips of the device.
  • Pull the unit straight out from the DIN rail.

Phase 3: Installation (10 min)

  • Hook the top clip of the isolator onto the DIN rail.
  • Press the bottom firmly until it clicks into place.
  • Wiring:
    • Power: Connect 20-35V DC to terminals 14 (+) and 15 (-).
    • Field Side (Input): Connect your 2-wire transmitter to terminals 1 (+) and 2 (-) or 3 (-).
    • Control Side (Output): Connect to your DCS/PLC AI card at terminals 7 (-), 8 (+), and 9.

Phase 4: Power-On & Test (10 min)

  • Restore the 24VDC power. The green LED on the front should illuminate.
  • Use a multimeter to verify the output current at terminals 8 and 9 matches the transmitter’s reading.
  • If using HART, connect a communicator across the output to verify digital signal transparency.

 

Troubleshooting Quick Reference

Symptom Probable Cause Quick Check / Solution
No LED on front Power supply off or reversed Measure 20-35V DC at terminals 14+ and 15-.
Output reads 0 mA Loop open or wiring error Check continuity on output terminals 7, 8, 9.
Signal unstable/noisy Ground loop or poor shielding Ensure cable shields are grounded at one end only.
HART communication fails Loop resistance too low Ensure total loop resistance is ≥ 250 Ω.
Output saturated (>25mA) Input overload or device fault Check field transmitter for short circuits.

 

Dimensions, Mounting & Wiring Notes

  • Dimensions: 20 mm (width) x 115 mm (depth) x 124 mm (height).
  • Mounting: Standard 35 mm DIN Rail (top-hat rail).
  • Terminal Notes: The unit uses screw-clamp terminals. Torque to 0.5 Nm.
  • HART Resistor: If the DCS input impedance is low, utilize the internal 250 Ω resistor by bridging terminals 8-9 and 11-12 (verify specific jumper settings in the manual).

FAQ

Q: Is this unit compatible with HART communicators?
A: Yes. The KFD2-STC4-1 is designed to be transparent to HART signals. It supports bidirectional communication with a bandwidth of up to 7.5 kHz.Q: I’m replacing an old KFD2-STC4-Ex1. Is this the exact match?
A: Yes, KFD2-STC4-1 is the standard designation often used interchangeably with KFD2-STC4-Ex1 in general catalogs. However, always double-check the SIL rating requirements of your specific safety loop before swapping.Q: Do I need an external power supply for the transmitter?
A: No. This isolator provides loop power to the field transmitter (terminals 1 and 2/3). It acts as an active barrier, supplying the necessary voltage (≥ 16 V at 20 mA) to drive the sensor.Q: What happens if the input loop breaks?
A: The device detects wire break conditions. The output will typically go into a predefined fault state (often dropping to 0 mA or going upscale, depending on configuration), alerting the control system.Q: Can I use this for non-smart (standard) 4-20mA transmitters?
A: Absolutely. While optimized for smart transmitters, it works perfectly fine with standard analog 2-wire transmitters. The “Smart” designation just means it won’t filter out the digital HART signal.Q: I noticed the label says “SIL 3”. Does this mean it’s fail-safe?
A: It means the device meets the reliability standards for SIL 3 applications according to IEC 61508. It is suitable for use in safety instrumented systems (SIS), but proper system architecture is still required to achieve the target SIL level.

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