Zener Barriers Vs Galvanic Isolators Key Safety Choices for Hazardous Areas

In petrochemical plants and other explosive environments, even a tiny electrical spark can trigger catastrophic consequences. Special safety barriers are essential to ensure that instruments connected to these hazardous areas remain absolutely safe under potential fault conditions. Two primary solutions exist: Zener Barriers (Intrinsic Safety Barriers) and Galvanic Isolators. This article examines their working principles, applications, and comparative advantages.

Zener Barriers, also known as ATEX Barriers or I.S. Barriers, function by restricting energy flow into hazardous areas. Their design ensures that even during faults, circuit energy remains below the minimum threshold required to ignite explosive mixtures.

While standard diodes permit current flow in one direction only, Zener diodes are engineered to conduct when reaching specific reverse voltage thresholds. In safety barriers, these components rapidly conduct excess current to ground when voltage exceeds safe limits, effectively clamping dangerous energy.

• Resistor: Limits current entering hazardous areas
• Zener diode: Clamps voltage during faults by diverting excess current to ground
• Fuse: Protects the Zener diode during overload conditions

During normal operation, the resistor restricts current flow. When voltage exceeds safe thresholds, the Zener diode activates to shunt excess current, while the fuse serves as final protection against equipment damage.

Proper functionality requires dedicated I.S. grounding installed according to IEC 60079-14 standards. This critical safety measure directly impacts system integrity.

Despite their simplicity and cost-effectiveness, Zener barriers present several constraints:

• Mandatory dedicated I.S. grounding increases installation complexity
• Additional loop loading may impair instrument performance
• Lack of signal conversion or amplification capabilities

These limitations have led to widespread replacement by galvanic isolators in modern installations.

Galvanic isolators like the PR 9000 series employ fundamentally different designs. While both technologies limit hazardous area energy, isolators implement three-port electrical isolation between input, output, and power circuits using transformers and optocouplers.

This complete electrical separation prevents ground loops and noise interference, significantly enhancing system reliability and safety.

The isolator's inherent electrical isolation eliminates special grounding requirements, dramatically simplifying installation and maintenance.

• Elimination of dedicated I.S. grounding
• Reduced loop loading for improved instrument performance
• Signal conversion and amplification capabilities
• Enhanced noise and surge resistance

• Temperature measurement (thermocouples/RTDs)
• Pressure transducer signal transmission
• Flow meter signal conditioning
• Explosion-proof valve control

Equipment destined for explosive environments requires certification to verify compliance with applicable protection methods. In the EU, ATEX certification is mandatory, while IECEx serves as the international standard.

• Certifying body identification
• Applicable standards
• Electrical parameters
• Installation specifications
• Special operating conditions

Proper I.S. loop design requires analysis of three components:

• Certified field equipment (hazardous area)
• Associated apparatus (safe area interface)
• Compatible interconnecting cabling

• Uo (Voc): Open-circuit voltage
• Io (Isc): Short-circuit current
• Po: Output power
• Ca: Permissible capacitance
• La: Permissible inductance

Simple calculations determine compatible equipment combinations and maximum cable lengths by comparing associated apparatus parameters with field device specifications. The system must satisfy:

• Uo ≤ Ui (voltage limitation)
• Io ≤ Ii (current limitation)
• Po ≤ Pi (power limitation)
• Ca ≥ Ctotal (capacitance limitation)
• La ≥ Ltotal (inductance limitation)

Adherence to these principles ensures intrinsically safe operation, minimizing explosion risks in hazardous locations.