Pepperl+Fuchs K-System Isolation Barrier Complete Guide

Pepperl+Fuchs K-System Barrier: Modular Solution for Intrinsic Safety Explosion proof Interface

Product Overview and System Positioning

In the field of process automation, field instruments (such as transmitters, solenoid valves, proximity switches) used in hazardous areas (such as chemical plants, refineries, pharmaceutical workshops) must exchange signals with the control system of the safe area, while ensuring that no energy sufficient to ignite explosive environments is generated. The K-System isolation barrier launched by Pepperl+Fuchs is the essential safety interface product series designed for this purpose. It is located between the danger zone (site side) and the safety zone (control side), providing not only limitations on current, voltage, and power, but also achieving galvanic isolation between the site circuit and the controller, thereby cutting off potential grounding circuits and surge paths.

The K-System is suitable for installation on 35mm DIN rails and includes over 150 different functions of equipment, including switch amplifiers, transmitter power supplies, temperature converters, frequency converters, solenoid valve drivers, HART multiplexers, and more. Its modular design makes the system easy to select, integrate, and expand. This manual systematically explains the mechanical structure, electrical connections, installation specifications, configuration methods, fault monitoring, and technical parameters of K-System, providing complete guidance for engineers in equipment selection and engineering implementation in hazardous areas.

Core functions and isolation principles

2.1 Intrinsic Safety Interface

The core task of K-System isolation barriers is to limit the energy transmitted to hazardous areas. According to the IEC 60079-11 standard, the electric sparks or thermal effects generated by intrinsically safe circuits under normal operation and specified fault conditions cannot ignite specific explosive gas environments. The isolation gate clamps the voltage and current output to the field side within safe values through Zener diodes, current limiting resistors, or more complex electronic circuits. At the same time, electrical isolation (usually using transformers or optocouplers) ensures that there is no direct electrical connection between the hazardous area circuit and the safe area circuit, and even if a high-voltage fault occurs in the safe area, it will not be transmitted to the site.

2.2 Signal Conversion and Conditioning

In addition to security restrictions, K-System devices also perform signal conditioning functions:

Convert 0/4-20mA analog signals from hazardous areas into standard signals for safe areas (also 0/4-20mA, or 0-10V, 1-5V, etc.).

Convert signals from NAMUR (EN 60947-5-6) proximity switches or mechanical switches into relay, transistor, or logic level outputs.

Provide isolated power supply (usually around 17V DC) for two-wire transmitters in hazardous areas.

Process sensor signals such as thermocouples, thermistors (Pt100), resistors, potentiometers, etc., and linearize the output.

Supports HART communication, allowing smart instruments to transmit analog signals while superimposing digital signals for easy configuration and diagnosis.

2.3 Fault Monitoring and Self Diagnosis

K-System equipment continuously monitors on-site line faults (disconnection, short circuit) and internal equipment failures. When a malfunction occurs, it can be reported through the following methods:

The red LED flashes or stays on (according to NAMUR NE44 standard).

Independent fault output (FAULT terminal, normally closed principle).

The aggregated error message is transmitted to the power feed module through the Power Rail, and then output by its relay contacts.

Shell design and modular system

K-System offers three housing widths based on functionality and power consumption, and all devices are compatible with 35mm DIN rail mounting (compliant with EN 60715).

3.1 KC Series -12.5mm Width

The KC device is the most compact version, suitable for simple signal conditioning or switch isolation. Its width is only 12.5 mm, making it suitable for high-density installation in cabinets. The terminal adopts removable terminal blocks, allowing users to pre wire the device without disassembling it. Terminal types available: screw terminals or spring terminals (model suffix. SP). In addition, the KC device is equipped with a transparent front cover to protect the operating components from contamination, and integrates a label rack for identification.

3.2 KF Series -20mm or 40mm Width

KF equipment offers two widths: 20mm for medium functional density (such as ordinary transmitter power supply, switch amplifier), and 40mm for more terminal requirements or higher power (such as solenoid valve drivers, HART multiplexers). It also uses pluggable terminals and can be equipped with test sockets for online signal measurement without interrupting the circuit. KF devices also have a transparent front cover, while some models do not have a front cover but are equipped with a label holder.

3.3 KH series -40mm width

The terminals of KH equipment (without pluggable terminals) are directly fixed on the housing and cannot be disassembled. Suitable for applications that do not require frequent replacement of wiring. Its width is also 40mm.

3.4 Anti misoperation and height identification of terminals

All pluggable terminals are equipped with red coding pins to prevent mixing of terminals between different devices. There are two heights for terminal blocks:

15mm height: Used for circuits with rated voltage below 50V AC, providing reinforced insulation.

15.5mm height: Used for circuits with rated voltage higher than 50V AC (up to 300V AC), providing basic insulation and marked with an "X" on the terminal side.

The tightening torque of the terminal screw is 0.5 Nm to 0.6 Nm, and the maximum cross-sectional area of the wire is 2.5 mm ² (14 AWG).

Color identification and status indication

4.1 Shell color coding

Pepperl+Fuchs uses color to quickly identify power supply types:

Green: DC 24V power supply.

Black: AC 115V/230V power supply.

Gray: AC/DC wide range power supply (e.g. 24V DC or 115/230V AC).

Blue: Equipment used for processing signals in hazardous areas (intrinsic safety side).

4.2 LED status light (compliant with NAMUR NE44)

All K-System devices are equipped with standardized LED indicator lights:

Green PWR (power supply): Constant light indicates normal power supply; Extinguishing indicates no power supply or insufficient power supply (equipment malfunction).

Red CHK (fault/channel):

Always on: Internal equipment malfunction (equipment replacement required).

Flashing: External circuit failure (such as disconnection or short circuit), on-site wiring needs to be checked.

Extinguish: No malfunction.

Yellow OUT (output status): Used for binary output or analog limit indication. Constant light indicates that the relay is engaged, the transistor is conducting, or the switch signal is valid; Extinguishing indicates disconnection.

In addition, some devices also provide additional yellow LEDs for input status indication.

Operating components and configuration methods

K-System devices support multiple configuration methods to adapt to applications of different complexities.

5.1 DIP switch

Used to select basic functions such as input type (NAMUR or mechanical contact), output mode (normally open/normally closed), filtering time, etc. The switch position is usually printed on the housing or attached to the manual.

5.2 Rotary switch

Used to select range, range, or address (such as a HART multiplexer). Multiple rotary switches can provide multiple discrete gears.

5.3 Potentiometer

Used for fine adjustment of zero position (ZERO) and full scale (SPAN), suitable for analog signal converters. Usually requires adjustment with a small screwdriver.

5.4 Keyboard and LC Display Screen

Some high-end devices (such as general signal converters) are equipped with LCD screens and buttons, which can directly browse measurement values, fault information, and modify parameters locally. Menu navigation usually uses the "ESC" and "OK" keys.

5.5 PACTware ™  Parameterized software

By connecting the programming socket on the device through a dedicated programming adapter (such as K-ADP-USB), the FDT/DTM framework software PACTware can be used to remotely configure, diagnose, and upgrade the firmware of the device. This is particularly useful for devices that require batch settings or complex logic, such as SMART transmitters with HART power supply.

5.6 Explosion proof precautions during configuration

When operating any switch, button, or potentiometer in a hazardous area, it is necessary to ensure that the environment is free of explosive gases, as mechanical action may generate sparks. In addition, static discharge (grounding or equipotential connection) should be performed before operation, and the transparent front cover should only be opened when necessary.

Installation and mechanical requirements

6.1 Installation direction and spacing

K-System equipment has low heat generation, allows for vertical or horizontal installation, and does not require spacing (can be arranged closely). But when the ambient temperature is above 60 ° C (up to 70 ° C), horizontal installation must be used and the minimum spacing must be maintained:

KC (12.5mm) equipment: ≥ 6mm

KF (20mm) equipment: ≥ 10mm

KF (40mm) equipment: ≥ 15 mm

6.2 DIN rail and power rail

Standard installation uses 35mm DIN rails (compliant with EN 60715). To further reduce wiring, K-System provides a Power Rail - a DIN rail with plastic inserts and built-in conductors. There are two versions of power rails:

UPR-03: 3-core (2-core power supply+1-core lumped error signal).

UPR-05: 5 cores (2-core power supply+1-core aggregate error+2-core serial data exchange, only used for specific devices such as KFD2-WAC2).

The power rail is equipped with a cover plate (UPR-COVER) and an end cover (UPR-E) at the factory to prevent contamination and accidental contact. Inject 24V DC power (up to 4A) into the guide rail through a power feeding module (such as KFD0-EB2 series), which can power up to 80 devices. The feed in module also provides replaceable 5A fuses and a lumped error relay output. Attention: It is strictly prohibited to supply power to the power rail through the isolation barrier itself, otherwise it may damage the equipment.

6.3 Traditional wiring (without power rail)

For devices powered by AC or general power, or in situations where power rails are not used, it is necessary to connect the power terminals of each device separately. This increases the workload of wiring and the risk of errors, but it is still inevitable in some renovation projects.

Precautions for Electrical Connections and Hazardous Areas

7.1 On site side connection

Terminals connected to hazardous areas (usually marked in blue) must meet the requirements of IEC/EN 60079-14 for isolation distance:

Adequate spacing (usually ≥ 6mm) should be maintained between two adjacent intrinsic safety circuits.

There must be reinforced insulation or reliable isolation between intrinsic safety circuits and non intrinsic safety circuits.

On site equipment (such as transmitters, NAMUR sensors, Ex ia valves) are connected through screws or spring terminals. For two-wire transmitters, isolation barriers provide loop power supply; For three or four wire Pt100, use the corresponding connection method.

7.2 Control side connection

The control side terminal is connected to the analog input/output module of PLC, DCS or other controllers. For relay output devices, the control side may involve 230V AC voltage, and safety regulations must be strictly followed: operate after power failure to prevent electric shock. For transistor outputs (such as 24V DC, 100mA), it should be ensured that the load does not exceed the rated value and attention should be paid to short-circuit protection.

7.3 Power Connection

DC powered equipment (green casing): typically accepts 20-30V DC (nominal 24V). It can be powered through power rails or independent terminals.

AC power supply equipment (black shell): accepts 115V AC or 230V AC (see nameplate for details), and must be powered by an isolation transformer or a power source that complies with SELV/PELV.

AC/DC wide range equipment (gray shell): can accept 24V DC or 115/230V AC, with high flexibility.

All power wiring must follow the low voltage command. When working on circuits above 50V AC or 120V DC, power must be disconnected, locked, and tested first.

Fault monitoring and centralized alarm

8.1 Line Fault Transparency (LFT)

Many K-System devices support Line Fault Transparency. This means that any wire breakage or short circuit that occurs on the on-site side will be detected and transmitted to the control side through the signal line in a way that exceeds the normal operating range (such as current<3.6mA or>21mA). In this way, the control system can detect on-site faults without the need for additional wiring.

8.2 Independent Fault Output

Some devices provide dedicated 'FAULT' output terminals (normally open or normally closed). Under normal conditions, the output is closed (or low level), and in the event of a fault, it is disconnected (or high level). This' closed circuit principle 'ensures that faults can be indicated even if power is lost.

8.3 Power rail aggregation error

When multiple devices are installed on the power rail, any device failure (line or equipment failure) will couple the aggregated error signal to the erroneous conductor of the rail. After the power input module detects this signal, it can be connected to the DI point or alarm light of the PLC through its relay contact (passive) output. This method greatly simplifies the wiring of multi-channel fault monitoring.

8.4 Signal range complies with NAMUR NE43

For 4-20mA signals, NE43 defines:

Measurement range: 3.8 mA to 20.5 mA.

Below the measurement lower limit:<3.6 mA indicates sensor failure or line disconnection.

Above the measurement limit:>21 mA indicates a fault (such as a short circuit).

The control system can identify signal validity and fault status based on this.

Technical specifications and performance parameters

9.1 Environmental conditions

Working temperature: standard -20 ° C to 60 ° C (some equipment can reach up to 70 ° C, subject to horizontal installation spacing).

Storage temperature: -40 ° C to 90 ° C.

Relative humidity: ≤ 95%, no condensation.

Corrosion resistant gas: Complies with ISA-S71.04 G3 grade (harsh).

Altitude: up to 2000 meters.

Vibration resistance: EN 60068-2-6, 10-150 Hz, 1g.

Impact resistance: EN 60068-2-27, 15g, 11ms, half sine.

9.2 Electrical Isolation and Safety

Functional isolation or safe isolation shall be in accordance with IEC 61140.

Intrinsic safety explosion-proof grade: Ex ia IIC (applicable to gas group IIC, temperature group T4/T6, etc.).

Certification: International certifications (ATEX, IECEx, CSA, UL, etc.).

The mean time between failures (MTBF) varies depending on the equipment, typically several decades.

9.3 Input/output signals

Analog inputs: 0/4-20 mA (HART compatible), 0-10V, 1-5V, Pt100, thermocouple, resistor, potentiometer.

Analog output: 0/4-20 mA (HART compatible), 0-10V.

Digital inputs: NAMUR (EN 60947-5-6), mechanical contacts, logic levels.

Digital output: Relay (2A, minimum load 1mA/24V), transistor (100mA/30V, short circuit protection), logic 24V.

Transmitter power supply: up to 17V DC.

9.4 Mechanical specifications

Shell material: polycarbonate (PC), flame retardant grade V2 (UL 94).

Protection level: IP20 (only applicable for cleaning and drying the interior of cabinets).

Dimensions: Various shapes, width 12.5/20/40/60 mm, height approximately 107-131 mm, depth 114-115 mm. Please refer to the data sheets of each model for details.

Model code analysis

The K-System model follows a systematic coding rule (e.g. KFD2-STC4-Ex1). The typical structure is as follows:

Position 1: K=K-System

Position 2: C (12.5mm pluggable terminal), F (20/40mm pluggable terminal), H (20/40mm non pluggable terminal)

Position 3: D (DC power supply), A (AC power supply), U (AC/DC wide power supply)

Position 4:0 (no power supply), 2 (24V), 4 (100V), 5 (115V), 6 (230V), 8 (24V DC or 115/230V AC)

Position 5: Function code (such as STC=SMART transmitter power supply with current output, SR=switch amplifier with relay output, TR=thermal resistance converter, etc.)

Subsequently, it may also include Ex identification, number of channels, etc.

The complete model definition needs to refer to the product data sheet.

Dismantling, maintenance, and scrapping

11.1 Disassembly steps

Disconnect the power supply and ensure that all circuits are out of power.

Insert a straight screwdriver into the groove of the red installation slider at the bottom of the device, and rotate it to make the slider pop out.

Repeat on the other side and remove the device from the DIN rail.

11.2 Maintenance Principles

The K-System equipment is not repairable (there are no user replaceable parts). If the equipment is damaged or malfunctioning, it must be replaced with original Pepperl+Fuchs spare parts. It is strictly prohibited to modify or repair explosion-proof equipment. When cleaning, only dry cloth should be used to avoid electrostatic discharge.

11.3 Scrap disposal

Recycle according to local electronic waste regulations. The equipment does not contain hazardous substances (compliant with RoHS), but should be avoided from being discarded indiscriminately.

Typical Applications and Selection Suggestions

12.1 Application Scenarios

Petrochemical industry: Transmit 4-20mA transmitter signals from Zone 1 to the safe zone while providing intrinsic safety power supply.

Pharmaceutical: Isolate solenoid valve drive to ensure safe operation of Ex ia valves in clean rooms.

Water treatment: Convert the NAMUR level switch signal into relay contacts to drive the pump.

Power: Isolation conversion of temperature sensor (Pt100) to avoid grounding loops.

Industrial gases: frequency signals (such as turbine flow meters) are converted into standard analog quantities.

12.2 Selection steps

Determine input signal type: 4-20mA active/passive? NAMUR？ Pt100？ Thermocouple? Frequency?

Determine the output signal type: 4-20mA to PLC? Relay to motor? Transistors to indicator lights?

Confirm power supply: Does the cabinet have a 24V DC power supply? Or is it only 230V AC? Is a power rail used?

Explosion proof rating: Ex ia IIC T4 is usually sufficient. Confirm the matching of intrinsic safety parameters of on-site equipment with isolation barriers (maximum allowable voltage, current, power).

Special feature: Do you need HART transparent transmission? Do you need line fault detection? Is SIL level (functional safety) required?

Width and density: Computer cabinet space, choose 12.5mm or 20mm equipment.