2 Types of PLCs – Modular vs Monolithic PLCs (Top 10 Differences)

All PLCs can be generally categorized into two types: Modular and Monolithic PLCs.

FeatureModular PLCsMonolithic PLCs
ConstructionConsist of a rack into which circuit “cards” are pluggedConsist of a monolithic “brick” containing all processor, I/O, and communication functions
I/O CapabilityComprises of racks where ample number of input and output (I/O) points can be plugged as desired. Limited in I/O capability
In Event of FailureEasy to repair, since only failed card needs to be replaced.Must be replaced as a whole in case of failure
CustomizationI/O configuration can be customized I/O configuration can’t be customized
Practical ApplicationUsed for monitoring and controlling of large-scale operationsUsed for small-scale processes
ExampleAllen-Bradley SLC 500 seriesGeneral Electric Series One PLC
Number of InputsCan be increased as desiredFixed
Fault detection and troubleshootingEasyDifficult

Also see: Top 10 Questions on PLCs

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