The Westermo MD-21-DC is a current loop converter that bridges RS-232 serial interfaces with 20 mA current loop systems in industrial environments. It enables transparent, long-distance data transmission with configurable active or passive receiver/transmitter modes, supporting up to 6 devices in multidrop loop topologies. The unit features galvanic isolation rated to 1500 V and is engineered for deployment across harsh operational conditions with minimal configuration overhead.
Technical Specifications
• Interfaces: 1 × 20 mA current loop (TTY), 2 × RS-232 (EIA RS-232-C/CCITT V.24)
• RS-232 Connectors: 9-position D-sub female or screw terminal; DCE configuration
• Maximum Data Rate: 19,200 bit/s (both RS-232 and current loop)
• Communication Modes: Asynchronous, full/half duplex or simplex
• Maximum Loop Distance: 6 km (3.7 miles)
• Multidrop Capacity: Up to 6 devices in loop configuration
• Power Supply: 12–36 VDC
• Power Consumption: Maximum 4 VA
• Galvanic Isolation: 1500 V via opto-coupler (data) and transformer (supply)
• Overvoltage Protection: Interface breakdown 37 V (20 mA loop); surge capacity 0.6 kW for 1 ms
• Operating Temperature: 5–50° C ambient
• Humidity: 0–95% RH, non-condensing
• Dimensions: 55 × 100 × 128 mm
• Weight: 0.4 kg
• Mounting: 35 mm DIN rail
– Key Features
• Selectable active or passive current loop operation
• Signal inversion capability via internal switch settings
• Total communication transparency requiring minimal field configuration
• Status indicators: Power (PWR), receive data (RD), transmit data (TD)
• Industrial EMC compliance: SS-EN 50081-1/SS-EN 55022 Class B, SS-EN 50082-2/SS-EN 61000-4-2
• Industrial shock and vibration approval
– Typical Applications
Current loop extension and RS-232 interface conversion in process control, SCADA, and legacy instrumentation networks requiring long-distance serial communication with noise immunity.
– Compatibility & Integration
Directly compatible with RS-232 devices and TTY applications. Functions as current source in 20 mA loop circuits.
