MTL 8937-HN Dual-Channel Zener Barrier
The MTL 8937-HN is a dual-channel Zener barrier from the MTL7000 Series, designed to provide intrinsic safety for 4-20 mA instruments located in hazardous areas (Zone 1 and Zone 2). It connects between safe area control systems (DCS, PLC) and hazardous area field devices such as pressure/temperature transmitters and smart valve positioners. The barrier uses Zener diode-reverse breakdown characteristics and current-limiting resistors to restrict voltage and current entering the hazardous area to safe levels, with a fuse providing fault protection. The module supports HART communication, allowing remote configuration and diagnostics from the control room without entering the hazardous area.
Technical Specifications
Product Type: Dual-channel Zener safety barrier
Series: MTL7000 Series
Number of Channels: 2 independent channels
Input Signal: 4-20 mA (from field instruments)
Hazardous Area Classification: Zone 1, Zone 2; IIC, T4-6
Maximum Operating Voltage: 28 V DC (loop-powered)
Safety Description: 28 V, 93 mA, 0.65 W (per channel)
HART Communication: Transparent pass-through (1 kHz signals)
Mounting: 35mm DIN rail
Terminals: Labeled "FIELD" (hazardous area) and "CONTROL" (safe area)
Protection: Fuse for overcurrent fault protection
Compliance: IEC 60079-14, IEC 60079-26, ATEX, IECEx, UL/CSA
Operating Temperature: -20°C to +60°C
Protection Rating: IP20
Zener Barrier Technology
The MTL 8937-HN uses a Zener diode-resistor-fuse architecture to provide intrinsic safety. Under normal operation, the Zener diodes do not conduct, allowing the 4-20 mA signal to pass through. If the voltage attempts to rise above the safe limit, the Zener diodes conduct, shunting excess current to ground. The series resistor limits current, while the fuse provides ultimate protection—if a fault causes excessive current, the fuse blows, permanently isolating the hazardous area circuit. The dual-channel design allows a single module to protect two independent signal loops, saving control cabinet space and reducing installation costs. The barrier is loop-powered, requiring no external power supply for operation.
Application Domains
The MTL 8937-HN is used in oil and gas (wellhead control, pipeline monitoring), chemical and petrochemical plants (reactor temperature monitoring), pharmaceutical manufacturing (sterile process monitoring), and power generation (turbine and boiler instrumentation). Its support for HART communication allows remote configuration and diagnostics of smart instruments from the control room, improving maintenance efficiency and safety.
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