PLC Midterm

PLC System Components

• The PLC connects all field devices to the CPU and acts as an interface between them.

PLC Memory System

• The PLC's memory system stores information about the status of all inputs and outputs.
• It uses a system to keep track of all this information, representing each bit as an information element indicating the status of external contacts or the presence/absence of power in a process circuit.

I/O Interface Modules

• The common type of I/O interface module is the digital module, which connects to ON/OFF nature field input devices like selector switches and limit switches.

Current in Devices

• If a device receives current when it is ON, it is said to be sinking current.
• If a device provides current when it is ON, it is said to be sourcing current.

Signal Types

• Unipolar signals can accept an input signal that varies in the positive direction only.
• Bipolar signals swing between a maximum negative value and a maximum positive value.

Encoder Interface

• The encoder interface allows the user to read the signal from an encoder on a real-time basis and stores this information so it can be read later by the processor.
• It provides pulse trains to a stepper-motor translator, which enables control of a stepper motor.