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2-Wire Transmitter Interface Signal Conditioners, Bandwidth 100 Hz

Each SCM5B42 2-wire transmitter interface module provides a single channel which accepts a 4 to 20 mA process current input and provides a standard + 1 to + 5 V or + 2 to + 10 V output signal . An isolated + 20 VDC regulated power supply is provided to power the current transmitter. This allows a 2-wire loop powered transmitter to be directly connected to the SCM5B42 without requiring an external power supply. The regulated supply will provide a nominal + 20 VDC at a loop current of 4 mA to 20 mA.

The SCM5B42 will provide a 1500 V isolation barrier for non-isolated 2-wire field transmitters. It can also be used when additional isolation is required between an isolated 2-wire transmitter and the input stage of the control room computer.

The voltage output is logic switch controlled, which allows these modules to share a common analog bus without the requirement of external multiplexers.

The SCM5B modules are designed with a completely isolated computer side circuit which can be floated to ± 50 V from Power Common, pin 16. This complete isolation means that no connection is required between I/O Common and Power Common for proper operation of the output switch. If desired, the output switch can be turned on continuously by simply connecting pin 22, the Read-Enable pin, to I/O Common, pin 19.

A precision 20 Ω current conversion resistor is supplied with the module. Sockets are provided on the SCMPB01/02/03/04/05/06/07 backpanels to allow installation of this resistor. Extra resistors are available under part number SCMXR1. All field inputs are fully protected from accidental connection of power-line voltages up to 240 VAC. The module has a 3 dB bandwidth of 100 Hz. Signal filtering is accomplished with a six-pole filter, with two poles on the field side of the isolation barrier, and the other four on the computer side.

Circuit diagram Dataforth SCM5B42

Block Diagram SCM5B42

PDF Downloads:

2 Modules for Type SCM5B42:

SCM5B42-02 4mA to 20mA SCM5B42 Isolated 2-Wire Interface Module with Voltage-Output
SCM5B42-01 4mA to 20mA SCM5B42 Isolated 2-Wire Interface Module with Voltage-Output


  • Input: mA-Signal
  • Output: +1V…+5V / +2V…+10V
  • Bandwidth 100 Hz
  • Isolation 1500 Vrms
  • Input protection 240 Vrms
  • Input Resistance 20 Ohm
  • Accuracy ± 0.03%
  • Linearity ± 0.005%
  • ANSI/IEEE C37.90.1 Input protection
  • CMR 100dB
  • Sensor excitation +20 V
  • NMR: 120dB / Decade > 100 Hz
  • Power Supply +5 VDC
  • Operating Temperature Range -40°C … +85°C
  • Mix and Match Types on Backpanels possible
  • Dimensions 58 x 57 x 15 mm
  • Optional DIN Rail Mounting
  • CSA certified, CE and ATEX compliant
  • Wide range of accessories
  • Special Solutions on request