20 mA Current loop converter

MD-21 DC


20 mA Current loop (TTY) converter

• Standard RS-232 interface
• Serial speed up to 19 200 kbit/s
• Distance up to 6 km (3.7 mi)

Easy to install and use

• Transparent communication
• Purpose built DIN rail casing with integral clip
• D-sub or screw terminal

Designed for use in harsh industrial applications

• AC or DC power options
• Total galvanic isolation & transient protection
• Industrial EMC, shock and vibration approval

Several configuration options

• Receiver/Transmitter active or passive
• Possibility to invert receiver and transmitter signals
• Possible to use in multidrop applications


The MD-21 is a 20 mA current loop (TTY) converter allowing RS-232 systems to be connected to a 20 mA current loop interface over a distance up to 6 km (3.7 mi).

The serial interface is a standard RS-232 interface with five control signals. Since the communication is totally transparent there is no need for different settings except for if the current loop shall be active or passive.

The MD-21 is designed for use in heavy duty industrial applications. The different power options, galvanic isolation, transient protection guarantees communication in the worst environments. The MD-21 has been tested to meet many EMC, isolation, vibration and shock standards, all to the highest levels suitable for heavy industrial environments.

The design of the current loop converter makes the MD-21 suitable for a variety of applications with various speed and data bit options. The converter can be used as a standard RS-232 to 20 mA current loop converter or connected in ring creating a multi-drop network. Being able to act as the current source on both transmit and receive circuits if required ensures that the MD-21 is suitable for any TTY application.

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Technical Specifications

20 mA Current loop converter
1 x 20 mA current loop up to 19.2 kbit/s
2 x RS-232 up to 19.2 kbit/s

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