Introduction to Electronics and Programmable Logic Controllers (PLCs)

Comprehensive vocabulary flashcards covering the fundamentals of electronics, electronic components, historical milestones, and programmable logic controller (PLC) concepts, architecture, and control methods.

Electronics

The study of the behavior and control of electrons under different conditions, particularly in electric fields, and how this behavior is used in electronic devices and circuits.

Electronic Devices

Components that control or influence the flow of electric charge, serving as the building blocks of electronic circuits (such as diodes, transistors, and integrated circuits).

Electric Current

The flow of electric charge through a conductor, primarily due to the movement of electrons in metal conductors.

Digital Electronics

The branch of electronics that deals with discrete signals, usually represented by binary values $0$ and $1$.

Analog Electronics

The branch of electronics that deals with continuously varying signals.

Microelectronics

The branch of electronics that focuses on very small electronic components and circuits.

Nanoelectronics

The branch of electronics that studies electronic devices and phenomena at nanometer scales.

Optoelectronics

The branch of electronics that combines electronics with light, such as in LEDs and photodetectors.

Semiconductor Devices

The branch of electronics that studies devices made from semiconductor materials, such as diodes and transistors.

J. A. Fleming

The inventor who developed the diode vacuum tube.

Lee De Forest

The inventor who developed the triode vacuum tube, which enabled signal amplification.

Bell Laboratories

The research facility that demonstrated the first working transistor in $1947$.

Jack Kilby

An engineer at Texas Instruments who developed a pioneering integrated circuit in $1958$, which was demonstrated in $1958$ and patented in $1959$.

Resistor

A component that limits electric current and reduces voltage in a circuit to protect components from excessive current.

Variable Resistor

A component that allows resistance to be adjusted to control current or voltage levels, such as in volume controls or light sensitivity adjustments.

Electrolytic Capacitor

A polarized capacitor that stores electrical charge and helps filter voltage fluctuations, typically marked with a negative stripe and a longer positive lead when new.

Ceramic Capacitor

A non-polarized capacitor that stores electrical charge, reduces electrical noise, and is used for noise suppression and high-frequency filtering.

Diode

A component that allows current to flow primarily in one direction, rectifies AC into pulsating DC, and prevents reverse current flow.

Transistor

A component that amplifies signals or acts as an electronic switch, available as NPN and PNP bipolar junction transistors.

Voltage Regulator

A device that maintains a relatively constant output voltage to provide stable voltage to electronic components (e.g., a $7805$ regulator providing a nominal $5\,\text{V}$ output).

Integrated Circuit (IC)

A compact semiconductor package containing many electronic components integrated into one chip to perform specific or complex electronic functions.

7-Segment LED Display

A display component consisting of seven individual LED segments arranged to display numerical digits from $0$ to $9$.

Relay

An electrically controlled switch that allows a control signal to switch a separate circuit.

Resistor Color Code System

A system of color bands printed on resistors to indicate resistance value, multiplier, and tolerance rating.

Programmable Logic Controller (PLC)

An industrial digital computer designed to monitor inputs, execute a programmed set of instructions, and control outputs in machines or processes.

Traditional Relay Control

A control system whose logic is built from physical wiring and relay contacts, which is less flexible and often requires rewiring when sequences change.

Input Module

A PLC component that receives signals from field devices (such as push buttons, switches, and sensors) and converts them into a form the CPU can process.

Central Processing Unit (CPU)

The main processing unit of a PLC that reads input status, executes the user program, performs logic and calculations, updates output status, and manages controller operations.

Output Module

A PLC module that sends control signals from the CPU to field devices such as indicator lights, relays, contactors, and valves.

Digital / Discrete Signal

A signal that represents distinct states, often ON/OFF or $1/0$, typical of push buttons, limit switches, and digital proximity sensors.

Analog Signal

A signal that represents a value that varies continuously over a range, such as temperature, pressure, flow, level, or position (e.g., $0\text{--}10\,\text{V}$ or $4\text{--}20\,\text{mA}$).

Scan Cycle

The repeated sequence in which a running PLC reads inputs, executes logic, and updates outputs.

Input Scan

The stage of the PLC scan cycle where the PLC reads the states or values from input modules and updates its input image or data.

Program Scan

The stage of the PLC scan cycle where the CPU evaluates the user program using current input and stored data.

Logic Execution

The stage of the PLC scan cycle where instructions, conditions, timers, counters, comparisons, and calculations are processed in program order.

Output Update

The stage of the PLC scan cycle where the PLC updates output states based on the results of program execution.

Housekeeping / Communications

The stage of the PLC scan cycle where the controller performs internal diagnostics, communication tasks, and system functions before repeating the scan.

ON/OFF Control

A control method that switches an output fully ON or fully OFF depending on whether a measured value is above or below a set point or threshold.

Deadband (Hysteresis)

Separate ON and OFF thresholds used in ON/OFF control to reduce rapid, repeated switching around the target value.

PID Control

Proportional–Integral–Derivative control; a method that continuously adjusts an output to reduce process error using present error, accumulated past error, and the rate of change of error.

Set Point

The desired target value for a controlled variable.

Process Variable (PV)

The measured value of the variable being controlled.

Error

The difference between the set point and the measured process value ($\text{Error} = \text{Set point} - \text{measured process value}$).

Proportional (P)

The term in a PID controller that responds directly to the current or present error.

Integral (I)

The term in a PID controller that responds to accumulated error over time to help eliminate steady-state offset.

Derivative (D)

The term in a PID controller that responds to how quickly the error changes to help anticipate future changes.

Sensor

A device that detects a physical condition or quantity.

Actuator

A device that produces physical action, such as moving a valve or mechanism.

Human–Machine Interface (HMI)

A visual interface that allows an operator to view system information and interact with a machine or process.

I/O

Input/Output; the signals and hardware modules that connect a controller to field devices.

Interlock

A condition or mechanism that permits or prevents an operation to ensure correct or safe sequencing.