The Westermo MD-42-AC is a short-haul modem for asynchronous data transmission over twisted pair cable, supporting full-duplex, half-duplex, or simplex operation. It bridges RS-232-C/V.24 and RS-422/RS-485 interfaces with galvanic isolation and transient protection, making it suitable for industrial and commercial environments requiring extended communication links at a fraction of repeater cost.
Technical Specifications
Data Transmission
• Asynchronous protocol; full-duplex, half-duplex, or simplex modes
• Maximum data rate: 115.2 kbit/s
• Maximum transmission range: 1200 m (0.3 mm² twisted pair at 42 pF/m capacitance)
• Fail-safe receiver state (OFF) when transmitter enters tri-state
Interface Support
• Primary: EIA RS-232-C/CCITT V.24, V.28, RS-423-A (9-pin D-sub female or screw terminal)
• Secondary: EIA RS-422/RS-485/CCITT V.11 (5-position screw terminal); supports multidrop bus topology only
• Termination recommended at master receiver and final slave unit
Electrical
• Power supply: 115 VAC or 230 VAC, +15/–10%, 48–62 Hz
• Power consumption: 4 VA maximum
• Fuse: 100 mA fast, 5×20 mm
Protection & Insulation
• Galvanic isolation: opto-coupler (data) and transformer (supply)
• Insulation voltage: 1500 V
• Mains overvoltage: 430 V breakdown (230 VAC) / 230 V breakdown (115 VAC)
• Interface overvoltage: 7 V breakdown (transmitter/receiver)
• Surge capacity: 0.6 kW for 1 ms
– Key Features
• Configurable switch settings for signal activation, DCD control, and CTS delay
• Status-controlled transmission (RTS/DTR) for RS-485 2-wire operation
• LED indicators: PWR, TD, RD, RTS, CTS, DCD
• 35 mm DIN-rail mounting; dimensions 55×100×128 mm; weight 0.5 kg
– Environmental Specifications
• Operating temperature: 5–50°C ambient
• Humidity: 0–95% RH non-condensing
– Compatibility & Integration
Designed for point-to-point and multidrop RS-485 networks. Bus structure topology required; star-shaped networks not supported. Shielded cable recommended for heavy industrial environments. Extended range achievable with lower-capacitance, larger-diameter cable.
