Monolithic PLCs Example – General Electric Series One PLC

Some low-end PLCs are strictly monolithic, with no ability to accept additional I/O modules. This General Electric Series One PLC (used to monitor a small-scale hydroelectric power generating station)  is  an example of a purely monolithic  design, having no “expansion”  slots  to  accept I/O cards:

A disadvantage of monolithic PLC construction is that damaged I/O cannot be independently replaced.  If an I/O  channel on one of these  PLCs  becomes damaged, the  entire  PLC must  be replaced to fix the problem. In a modular system, the damaged I/O card may simply be unplugged from the rack and replaced with a new I/O card. Another disadvantage of monolithic PLCs is the inherently fixed nature of the I/O: the end-user cannot customize the I/O configuration to match the application.  For these reasons, monolithic PLCs are usually found on small-scale processes with few I/O channels and limited potential for expansion.

Article from Lessons In Industrial Instrumentation by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License

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