Contactor,circuit breaker,sensor,Encoder,PLC,Converter
Series: K-System, 2-channel NAMUR switch isolator
Replaces legacy model KFD2-SR-Ex2
Designed for hazardous area Zone 0/1/2. Accepts NAMUR sensors or dry contact signals, with passive relay contact outputs. Supports line fault detection (wire break/short circuit LFD), signal inversion via DIP switches, SIL2 (SC3) functional safety rating.
📌 Terminal Assignment
Channel 1 Input: 1+, 2+, 3-
Channel 2 Input: 4+, 5+, 6-
Channel 1 Relay Output (changeover contact): 7, 8, 9
Channel 2 Relay Output (changeover contact): 10, 11, 12
Power supply: 14+ /15-. Can also be powered via K-System Power Rail backplane, which provides collective fault signal output.
📋 Key Specifications
| Item | Parameter |
| Supply Voltage | 19~30V DC, ≤50mA, power consumption ≤1W |
| Intrinsically Safe Side Input | 8V open circuit, 8mA short circuit; NAMUR standard EN60947‑5‑6; switching threshold 1.2~2.1mA, hysteresis 0.2mA |
| Line Fault Detection | Wire break: I ≤0.1mA; Short circuit: I＞6mA |
| Max. Input Frequency | ≤10Hz, minimum pulse/quiescent time 20ms |
| Relay Contact Rating | AC250V/2A (cosφ>0.75); DC40V/2A resistive load |
| Response Time | Approx. 20ms pull‑in / 20ms drop‑out |
| Isolation | Reinforced isolation between input/output/power, 300Veff |
| Explosion Protection Approvals | ATEX PTB 00 ATEX 2080; IECEx, FM, cULus; II(1)G [Ex ia Ga] IIC |
| Ambient Temperature | -40 ~ +70℃ |
| Mounting | 35mm DIN rail, housing width 20mm, IP20 |
| Safety Rating | SIL2, SC3 (IEC61508) |
| Configuration | DIP switches on housing for channel logic inversion |
⚠️ Distinguish Variant Suffixes
KFD2-SR2-Ex2.W: Standard 2-channel NAMUR switch amplifier (general purpose)
KFD2-SR2-Ex2.W.SM: Shutdown / direction monitor, with frequency threshold, start-up inhibit, max. 2kHz. Do not interchange.
🛠️ Typical Applications
Explosion-proof loops: NAMUR proximity sensors, valve position feedback, explosion-proof dry contacts. Isolated switch signal transmission to PLC/DI cards with wire break and short-circuit fault alarms. Widely used in chemical, pharmaceutical and oil & gas hazardous DI loops.
🔍 Troubleshooting Guide
- Sensor fails to trigger: Verify intrinsically safe loop parameters and DIP inversion setting.
- Persistent fault alarm: Measure input current to discriminate wire break or short circuit.
- Relay does not actuate: Check contact load rating and supply voltage drop.
- Collective fault on Power Rail: When multiple KFD modules share the backplane, any module fault triggers collective alarm.
📎 Replacement Reference
Same platform alternative: KFD2-SR2-Ex1.W (single-channel version). For domestic isolator replacement, select SIL2 rated units with NAMUR input and relay output. Intrinsically safe parameters Uo/Io/Po must match (10.5V/13mA/34mW).
KFD2-SR2-Ex2.W is a standard 2-channel NAMUR switch amplifier for static DI signals with max. 10Hz. Not the SM version for speed/direction high-frequency pulse monitoring. All cases below apply only to KFD2-SR2-Ex2.W.
Case 1: Explosion-proof Valve Position Feedback (Chemical / Oil & Gas, Most Common)
Scenario: Tank farm, reactor, pipeline shutoff valves (Zone1 IS area) fitted with NAMUR valve position feedback switches for fully open / fully closed status.
Field devices: 2 NAMUR 2-wire proximity switches assigned to Channel 1 and Channel 2 separately.
Isolator: KFD2-SR2-Ex2.W, enable LFD line fault detection via DIP; enable channel inversion (S1/S2) as required for DCS logic.
Safe side: Two relay changeover contacts wired to DCS DI cards.
Benefits:
- Intrinsically safe isolation to meet Ex ia IIC requirements.
- Wire break and short circuit alarm, preventing undetected loss of valve feedback.
- SIL2 rated for valve feedback loops of SIS safety shutoff valves.
Logic description: Valve in position → NAMUR switches → isolator relay energizes → DCS receives valve open/closed signal; cable break/short → relay de-energizes, fault LED on, collective fault uploaded via Power Rail.
Case 2: Explosion-proof Float Level Switch (Pharmaceutical, Fine Chemical Overflow / Low-Level Interlock)
Scenario: High level overflow alarm and low level pump protection for hazardous storage tanks with NAMUR float switches.
Configuration: One module handles 2 float signals (high-high level and low-low level).
Notes: For passive dry-contact floats, switch to dry contact mode (disable LFD); enable LFD for NAMUR type.
Interlock usage: Relay outputs feed SIS or PLC safety loops. Level trip triggers pump stop or inlet valve closure.
Advantage: Compact footprint; one module replaces two single-channel isolators to save cabinet space.
Case 3: Explosion-proof Conveyor Guard Door & E-Stop Loop (Dust Explosion Zone21/22, SIL2 Safety Loop)
Scenario: Powder conveying lines, hazardous waste packaging lines. IS guard door switches and IS emergency stop pushbuttons (dry contact) in hazardous area.
Wiring: Channel1 = guard door switch; Channel2 = local emergency stop.
DIP setting: Configure inversion according to safety logic (de-energize-to-trip principle: normal = energized, fault/wire break/trip = de-energized, compliant with safety de-energization rules).
Safety design: Passive relay contacts to safety PLC DI. Cable break is treated as emergency stop command to initiate machine shutdown, conforming to NE44.
Note: This model is for static switch signals only. Not suitable for high-speed pulse speed measurement (use SM variant).
Case 4: Local Status Feedback for Explosion-proof Pumps and Agitators (Dry-Contact Pressure / Temperature Switches)
Scenario: Hydrogenation, solvent recovery units. Field IS pressure and temperature switches (passive dry contacts) for high pressure / high temperature alarm.
Field equipment: Passive mechanical switches (no external supply).
Setting: Disable LFD (LFD does not support dry contact operation).
Output: Two relay signals to DCS for alarm indication.
Comparison: Enable LFD for NAMUR sensors for cable damage diagnostics.
Case 5: Multi-Module Cluster with Power Rail Collective Fault Summary (Large DCS/SIS Cabinets)
Scenario: Concentrated valve and level DI signals inside an isolation cabinet with many KFD2 modules mounted on K-System Power Rail backplane.
Power supply: Unified 24V supply via backplane; no separate power wiring for each module.
Collective fault: Backplane provides one common dry contact fault signal. Any SR2-Ex2.W wire break, short circuit or module fault activates the collective fault contact.
Application: Feed one “isolator bank fault” alarm point to DCS for rapid troubleshooting.
Engineering benefit: Reduces discrete fault DI points and simplifies SIS diagnostic architecture.
Case 6: Flare Stack and Vent Line Flame Detector Auxiliary Switch Signal
Scenario: Hazardous flare stacks fitted with NAMUR flame switches (discrete flame present signal, not 4-20mA analog).
Channel1: Flame presence detection; Channel2: Purge gas pressure switch.
SIL2 certified for SIS flame failure interlock.
Limitation reminder: Flame flickering frequency must not exceed 10Hz; high-frequency pulses are not supported.
General Selection & Common Pitfalls
- Input rule: NAMUR sensor → enable LFD; passive dry contact → disable LFD. LFD enabled on dry contact loops causes constant fault alarm.
- Max switching frequency ≤10Hz, minimum pulse period ≥20ms. Speed and direction monitoring with high-frequency pulses must use KFD2-SR2-Ex2.W.SM, not this model.
- SIL2 application: Complete PFH and SFF calculation per SIL safety manual. Passive relay contacts are suitable for SIS DI acquisition.
- Relay load limit: AC250V/2A, DC40V/2A. Do not drive high-power solenoid valves directly; use only for signal transfer.
- Terminal segregation: IS side terminals (1~6) connect to field Ex area; relay side terminals (7~12) are safe area. No cross wiring permitted.
Pepperl+Fuchs K-System Isolator Model & Order Code List (Common Engineering Types)
Notes: KFD2 = Power Rail backplane powered; KFD0 = loop powered; KCD2 = new compact 12.5mm narrow housing. Suffixes .W / .D / .IO / .SM denote functional variants. All are Ex ia IIC IS isolators with SIL2/SIL3 ratings. Legacy KFU series is gradually superseded by KFD2/KCD2.
- NAMUR / Digital Input (DI, including KFD2-SR2-Ex2.W)
| Order Code | Description | Channels | Remarks |
| KFD2‑SR2‑Ex1.W | NAMUR Switch Amplifier | 1CH | Single‑channel NAMUR/dry contact, relay changeover output, LFD |
| KFD2‑SR2‑Ex2.W | NAMUR Switch Amplifier | 2CH | Dual‑channel NAMUR, relay contact output (focus model) |
| KFD2‑SR2‑Ex2.W.SM | Speed / Direction Monitor | 2CH | High‑frequency pulse up to 2kHz, start inhibit, direction detection, not interchangeable with standard SR2 |
| KFD2‑SOT3‑Ex2.IO | NAMUR Isolator, Transistor Output | 2CH | NAMUR input, passive transistor output, no relay, SIL2 |
| KFD0‑RO‑Ex2 | Loop‑powered Relay Isolator | 2CH | Loop powered, 2 logic inputs, relay output, SIL3 |
| KCD2‑SR‑Ex1 | Compact NAMUR Isolator | 1CH | 12.5mm narrow housing, NAMUR input transistor output |
- 4-20mA Analog Input (AI, 2-wire Transmitter, HART)
| Order Code | Description | Channels | Remarks |
| KFD2‑STC4‑Ex1 | Smart Transmitter Isolator | 1CH | Single‑channel 4‑20mA, HART, backplane powered, SIL2 |
| KFD2‑STC5‑Ex2 | Smart Transmitter Isolator | 2CH | Dual‑channel 4‑20mA+HART, 20mm width, cabinet space saving, SIL2 |
| KFD0‑CS‑Ex1.50P | Loop‑powered Current Repeater | 1CH | Loop powered, 4‑20mA isolation, HART, SIL2 |
| KFD0‑CS‑Ex1.51P | Loop‑powered Current Isolator | 1CH | Low voltage drop version for low supply loops |
| KFD2‑CRG2‑Ex1.D | AI Isolator with Alarm Relays | 1CH | 4‑20mA input, 2 programmable high/low alarm relays |
| KCD2‑STC‑1.2O | Compact HART Isolator | 1CH | 12.5mm, 1‑in 2‑out 4‑20mA splitter, safe side only |
- Analog Output (AO, Drive IS Valve Positioners in Hazardous Area)
| Order Code | Description | Channels | Remarks |
| KFD2‑SCD2‑Ex1.LK | IS 4‑20mA Output Isolator | 1CH | Safe side to hazardous side AO, drive IS positioner, HART |
| KCD2‑SCD‑Ex1 | Compact AO Isolator | 1CH | 12.5mm, HART, SIL2 |
- Solenoid Drivers (SIS IS Solenoids, Mostly SIL3)
| Order Code | Description | Channels | Remarks |
| KCD2‑SLD‑Ex1.1245 | Solenoid Driver Isolator | 1CH | 12V/45mA, LFT transparent line diagnosis, test pulse immunity, SIL3 |
| KFD2‑SL2‑Ex1 | Solenoid Driver Module | 1CH | Classic IS solenoid driver |
- Temperature Isolation (RTD / TC Thermocouple)
| Order Code | Description | Channels | Remarks |
| KCD2‑UT2‑Ex1 | Universal Temperature Converter | 1CH | Pt100/Thermocouple/mV, 4‑20mA output, PACTware configurable, SIL2 |
| KFD0‑TR‑Ex1 | Loop‑powered RTD Isolator | 1CH | Pt100, wire break detection, no backplane required |
| KCD2‑RR2‑Ex1 | RTD Resistance Repeater | 1CH | Passive resistance signal transmission without current conversion |
- Frequency / Pulse, Speed Isolation (FI, Flowmeter, NAMUR Speed Probe)
| Order Code | Description | Channels | Remarks |
| KFD2‑UFC‑Ex1.D | Frequency Converter Isolator | 1CH | NAMUR/dry contact pulse input, 0~5kHz, 4‑20mA + alarm relay, SIL2 |
| KFU8‑UFC‑Ex1.D | Universal Frequency Isolator | 1CH | Legacy standalone supply, superseded by KFD2‑UFC‑Ex1.D |
- Voltage Signal Isolation (Vibration, mV Sensors)
| Order Code | Description | Channels | Remarks |
| KFD2‑VR2‑Ex1.50M | mV Signal Repeater | 1CH | Small mV signal for vibration sensor isolation |
| KFD2‑VR4‑Ex1.26 | Negative Voltage Repeater | 1CH | For -20V vibration probes (B&K etc.) |
- Backplane Power Modules & Accessories (For KFD2 Power Rail System)
| Order Code | Description | Remarks |
| KFD2‑EB2 | Power Feed Module | Basic backplane supply and fault summary |
| KFD2‑EB2.R4A.B | Redundant Power Feed Module | Dual 24V input, 4A, fault relay, widely used in SIS cabinets |
| KFD2‑EB2.R4A.B.SP | Redundant Feed, Spring Terminal | Push‑in spring wiring version |
| KCD0‑LGH | Blank Filler Module | 12.5mm blank filler and jumper adapter |
| K‑System Power Rail DIN Rail | Power Bus Rail | Screw terminal / spring terminal variants |
- Model Naming Rules
- KFD2: Power Rail backplane powered; KFD0: loop powered; KCD2: new compact 12.5mm module
- Middle code SR / STC / SCD / UFC / UT / SLD = signal type
SR: NAMUR switch amplifier
STC: transmitter supply AI
SCD: analog output AO
SLD: solenoid driver
UFC: frequency / speed
UT: universal temperature
- Ex1 / Ex2: Channel quantity
- Suffix .W / .D / .IO / .SM / .LK: Functional variant
W: Relay contact output (e.g. KFD2-SR2-Ex2.W)
SM: Speed and direction dedicated
D: With alarm relay and configurable parameters
IO: Passive transistor output
LK: Low-power HART AO
⚠️ Critical Selection Notes (Frequent Site Mistakes)
- KFD2-SR2-Ex2.W (≤10Hz static DI) ≠ KFD2-SR2-Ex2.W.SM (2kHz speed measurement). Not interchangeable.
- KFD0 loop-powered: No backplane supply, powered from 4-20mA loop. KFD2 requires Power Rail bus rail.
- SIL3 loops prefer KCD2-SLD-Ex1.1245. General DI/AI are mostly SIL2 SC3.
- HART support only for STC / SCD types. SR switch isolators do not support HART.
