Each C5B 31 voltage input module provides a single channel of analog input
which is filtered, isolated, amplified, and converted to a high-level analog
voltage output. This voltage output is logic-switch controlled, allowing these
modules to share a common analog bus without the requirement of external
The C5B 31 modules are designed with a completely isolated computer-side
circuit which can be floated to ±50V 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).
Signal filtering is accomplished with a six-pole filter, which provides 95dB
of normal-mode-rejection at 60Hz and 90dB at 50Hz. Two poles of this filter are
on the field side of the isolation barrier, and the other four are on the
After the initial field-side filtering, the input signal is chopped by a
proprietary chopper circuit. Isolation is provided by transformer coupling,
again using a proprietary techniques to suppress transmission of common mode
spikes or surges. The module is powered from ±5VDC (±5%).
A special input circuit on the module provides protection against accidental
connection of power-line voltages up to 240VAC.