Programmable Logic Controller

Written by Jerry Ratzlaff on . Posted in Instrumentation & Controls

There are four primary types of signals that the programmable logic controller (PLC) generates.  On a P&ID, when referencing the type of signal for a particular instrument or installation, it should be in reference to the PLC.  The types of signals are analog output (AO), analog input (AI), discrete output (DO), and discrete Input (DI).


instrument abbreviations