There are other discrete modules that have been developed for specialized needs.
Some of these options are listed below.
Contact Output Modules:
In these modules, power is supplied “in” and then flows “out” when the contact is closes.
This module is designed so that many different sources of power can be used, but they remain isolated from one another.
Interposing Relay Modules:
This is an electrical unit used for hardwired signals with digital inputs and outputs.
These I/Os interface between the control and circuit breakers or a controller.
This module is necessary because it separate the circuits and allows them to switch between high and low voltages and currents.
This module is most beneficial when the solenoid has a different voltage than the PLC.
TTL I/O Modules:
Allows transmitting and receiving of Transistor-Transistor-Logic (TTL) signals.
This module “translates” the signals of devices that produce TTL signals so that they can communicate with the PLC’s processor.