KONGSBERG DZ-120 Zener Safety Barrier Unit

KONGSBERG DZ-120 Zener Barrier Unit: Reliable Guarantee of Intrinsic Safety Interface

Product Overview

The DZ-120 Zener safety barrier is a single channel shunt diode type safety barrier specifically designed to protect two-wire 4-20mA/HART transmitters installed in hazardous areas. It safely transmits power and signals from the safe area to the hazardous area through energy limiting circuits, ensuring that under any fault conditions, the electrical energy transmitted to the hazardous area is below the minimum required for ignition.

This unit is designed to be compact and can be easily mounted on DIN rails, making it suitable for dense installation in control room cabinets. The blue terminal clearly indicates the intrinsic safety side for easy identification of on-site wiring.

Working principle

The core protection mechanism of the Zener safety barrier is based on voltage limitation and current limitation:

Voltage limitation: A Zener diode is connected in parallel between the safety side terminal (connected to the control system) and ground. When there is a fault overvoltage on the safety side (such as power surge, internal short circuit), the Zener diode conducts, clamping the voltage on the dangerous side below the safe value. The maximum output voltage Uo of DZ-120 is limited to 26.5V DC.

Current limitation: Connect a precision resistor (nominal 265 Ω) in series in the circuit to ensure that even if a short circuit occurs in the hazardous side cable, the current flowing through the area will not exceed the safety threshold. The maximum output current Io of DZ-120 is 112mA.

Fuse protection: The 50mA fuse connected in series inside will melt when the Zener diode continues to conduct, cutting off the fault circuit and preventing the Zener diode from being overloaded and burned out.

Through these triple protections, DZ-120 ensures that hazardous area instruments will not receive enough energy to ignite explosive gases under any circumstances. At the same time, the design allows for a short circuit of the hazardous side cable without causing any danger.

Installation and wiring

Installation location

DZ-120 must be installed in a secure area cabinet, usually located in the control room or processing cabinet. The installation environment must meet the following special conditions:

The cabinet protection level should be at least IP22

Maintain a minimum distance of 50mm between intrinsic safety circuits and non intrinsic safety circuits

Environmental temperature range: -20 ° C to+70 ° C

Grounding requirements

The grounding of intrinsic safety systems is crucial. The grounding terminal T6 of DZ-120 must be connected to the intrinsically safe busbar of the system through a cable of at least 1.5mm ². The busbar should be reliably grounded to ensure that the Zener diode can effectively clamp in the event of a fault.

Terminal function

T4, T5 (blue): Connect the 2-wire transmitter in the hazardous area to form an intrinsic safety circuit.

T2, T3: Simulate input channels for monitoring systems connected to secure areas (such as AI cards for PLCs and DCS).

T6: Grounding terminal, connected to the intrinsic safety grounding busbar.

Mechanical Installation

DZ-120 is designed for TS-35 mounting rails (compliant with DIN46277) and is fixed using a card mounting method. It is recommended to use end stops at both ends of the guide rail to prevent sliding.

HART communication compatibility

DZ-120 not only transmits 4-20mA analog signals, but also has a pre-set HART communication path. The HART protocol superimposes frequency signals on 4-20mA for remote configuration, diagnosis, and digital variable reading of transmitters. The resistance characteristics of the Zener safety barrier have been optimized to ensure reliable digital communication of the HART signal.

Technical Specifications

Electrical parameters

Power supply: 24 VDC nominal (± 0.5V)

Nominal resistance: 265 Ω

Maximum series resistance: 270 Ω

Maximum load resistance: 150 Ω

Rated value of fuse: 50 mA

signal interface

4 - 20 mA / HART

environmental conditions

Working temperature: -20 ° C to+70 ° C

Storage temperature: -25 ° C to+70 ° C

Relative humidity: maximum 75% (no condensation)

mechanical parameters

Dimensions: 12.5 x 114.5 x 99.0 mm (width x height x depth)

Protection level: IP20

Weight: 0.1 kg

Terminal capacity: 2.5 mm ²

Security data (entity parameters)

To ensure the correct selection and safe use by system designers, DZ-120 provides the following key safety parameters (based on EN/IEC 60079-11):

Parameter numerical description

Um 250 VAC maximum safe voltage (maximum non intrinsic safety voltage that the terminal block can withstand)

Uo 26.5 VDC maximum output voltage (open circuit voltage)

Io 112 mA maximum output current (short-circuit current)

Po 0.74 W maximum output power

Co 95 nF maximum allowable external capacitance (distributed capacitance for connecting hazardous side cables and instruments)

Lo 2.8 mH maximum allowable external inductance (distributed inductance for connecting hazardous side cables and instruments)

Lo/Ro 48 μ H/Ω maximum ratio of inductance to resistance

Important: The total capacitance of cables and instruments connecting hazardous areas must not exceed Co, and the total inductance must not exceed Lo, otherwise it may store excessive energy and compromise intrinsic safety.