Pepperl+Fuchs K-System Isolation Barrier Complete Guide

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).