Zener Barriers Enhance Safety in Hazardous Industrial Areas

In flammable and explosive environments, ensuring the safe operation of electrical equipment presents significant challenges. Zener barriers, serving as intrinsic safety-type explosion-proof devices, play a critical role in these hazardous areas. By effectively limiting voltage and current, they prevent the ignition of combustible gases and dust, providing reliable protection for electrical systems in dangerous locations.

As passive safety devices, Zener barriers perform the essential function of restricting electrical energy entering hazardous zones to levels below the ignition threshold of potentially explosive atmospheres. They establish safe electrical connections between non-hazardous and hazardous areas, ensuring that even during equipment failures, no sparks or heat capable of igniting explosive mixtures can occur.

The operation of Zener barriers relies on the characteristics of Zener diodes, combined with resistors and fuses to provide dual protection through voltage clamping and current limitation.

• Voltage Clamping: Zener diodes connect in parallel with circuits, remaining non-conductive during normal operation. When voltage exceeds their breakdown threshold (Zener voltage), the diodes rapidly conduct, clamping voltage to safe levels and preventing overvoltage from entering hazardous areas.
• Current Limitation: Circuit resistors regulate current flow, ensuring energy entering hazardous zones remains below ignition thresholds. Resistor selection requires precise calculation based on specific applications and safety requirements.
• Fuse Protection: Serving as additional safeguards, fuses immediately break circuits during faults, cutting power to prevent potential ignition sources.

Various Zener barrier types exist to meet different application needs:

• Single-Channel Barriers: Designed for simple signal transmission with positive or negative polarity, suitable for grounded circuits.
• Dual-Channel Barriers: Similarly handle simple signals with positive or negative polarity for grounded circuits while processing two signals simultaneously.
• Barriers with Feedback Diodes: Specifically engineered for 4-20mA current loops, offering precise current control and signal feedback.
• AC or Bipolar Signal Barriers: Transmit alternating current or bipolar signals in grounded circuits.
• Star-Connected Barriers: Utilize star connection configurations for enhanced safety and reliability.

The MM 7… series represents simple intrinsically safe interfaces specifically designed to protect electrical circuits in explosive hazardous areas. Proper circuit grounding with resistance below 1 ohm proves essential for their correct operation.

The INJBB 7028+ serves as an intrinsically safe barrier for positive polarity voltage or current, featuring P12 packaging. This single-channel device offers the following connections:

• 1: + input/output
• 7: + input/output (Ex, hazardous area)
• 3, 4, 5, 6, 9: GND (ground)

Applications include:

• Hazardous Area Analog Outputs: Controlling valves, position sensors, or powering optical/audio signaling devices in dangerous locations.
• Hazardous Area Analog Inputs: Transmitting electrical signals from hazardous zones, including photodiodes or devices with independent power supplies.
• Hazardous Area Binary Inputs/Resistance Inputs: Measuring resistance of hazardous area equipment like temperature sensors or potentiometers, or transmitting binary signals from OC relays, TTL outputs, and CMOS devices.

The INJBB 7048+ functions as an intrinsically safe barrier for positive polarity dual-channel analog outputs with the same connection scheme as the 7028+. Its applications mirror those of single-channel barriers but accommodate dual-channel requirements.

Designed for AC or bipolar signals, the INJBB 7055+ comes in P12 or P17 packaging (with replaceable fuses) and provides:

• 1: + input/output 1
• 2: + input/output 2
• 7: + input/output 1 (Ex, hazardous area)
• 8: + input/output 2 (Ex, hazardous area)
• 3, 4, 5, 6, 9: GND (ground)

This barrier supports:

• Hazardous Area Analog Outputs: Controlling or powering variable electrical circuits like audio/video signals, frequency/phase control systems, or bipolar unidirectional servo motors.
• Hazardous Area Analog Inputs: Transmitting variable electrical signals including audio/video data, vibration sensor outputs, or safety equipment signals.
• Three-Wire Resistance Outputs: Measuring three-wire resistances from hazardous area devices such as temperature sensors, position sensors, or potentiometers.

Proper selection and implementation of Zener barriers requires consideration of multiple factors:

• Application Environment: Different scenarios demand specific barrier types and parameters.
• Signal Characteristics: Barrier selection must match transmitted signal types (analog, digital, AC, etc.).
• Safety Ratings: Barriers must comply with hazardous area classification requirements.
• Installation and Maintenance: Strict adherence to standards and regulations ensures reliable operation.

As mature and reliable intrinsic safety technology, Zener barriers find widespread use in petroleum, chemical, mining, pharmaceutical, and other explosion-risk industries. Their proper selection and application significantly reduce safety risks while ensuring operational security.