Logic Controls Exam 1

Analog

A quantity that varies continuously over a range of values.

Digital

A quantity that exists in only discrete states (on/off or 1/0).

Bit

The smallest unit of digital information, represented as a 1 or 0.

Pulse

A brief change in voltage level from one state to another and back.

Clock

A signal that produces a steady stream of pulses used to synchronize digital circuits.

Timing Diagram

A graphical representation showing how digital signals change over time.

Data

Information represented in binary form for processing or transmission.

Serial

Data transfer method where bits are sent one at a time over a single line; slower but uses fewer wires.

Parallel

Data transfer method where multiple bits are sent simultaneously over multiple lines; faster but uses more wires.

Logic

The use of switches, gates, or circuits to perform decision-making based on inputs.

Input

A signal or device that sends information into a circuit or PLC.

Output

A signal or device that receives commands from a circuit or PLC.

Gate

A basic digital circuit that performs a logical operation (AND, OR, NOT, etc.)

NOT / Inverter

A logic gate that outputs the opposite of its inputs.

AND

A logic gate that outputs 1 only when all inputs are 1.

OR

A logic gate that outputs 1 when at least one input is 1.

Register

A digital storage element that holds one or more bits; can shift data serially or in parallel.

PLC

Programmable logic controller; an industrial computer designed to control machinery.

Switch

A device that maintains its state after being actuated.

Button

A device that returns to its original state after being released.

Normally Open

A contact that is open in its resting state.

Normally Closed

A contact that is closed in its resting state.

Relay

An electrically operated switch that uses an electromagnet to open and close contacts.

Binary

A number system using only 0 and 1; base 2.

Amplitude

The voltage level of a digital waveform.

Period

The time it takes for one complete cycle of a waveform.

Frequency

The number of cycles per second of a waveform; measured in Hz.

Shift Register

A register that moves bits through its stages, one position per clock pulse.

Radix / Base

The number of unique digits in a number system.

Latch

A circuit that maintains its output state after triggering inputs is removed, using a parallel contact to “seal in” the coil.

Parity Bit

An extra bit added to binary data to detect transmission errors.

Even Parity

A parity scheme where the total number of 1s in a data word is even.

Odd Parity

A parity scheme where the total number of 1s in a data word is odd.

Boolean Expression

An algebraic expression representing the logic of a circuit using AND, OR, and NOT operations.

Truth Table

A table that shows all possible input combinations for a logic gate and the resulting output.

De Morgan’s Theorem

States that the complement of a product equals the sum of complements, and vice versa: NOT(A*B) = NOT A + NOT B

PLC Address

The physical or logical location identifier for an I/O point in a PLC program.

Line Diagram

A schematic that shows the electrical control logic of a circuit using horizontal lines between two power rails (L1 and L2).

Wiring Diagram

Shows the actual physical wiring connections and locations of components.

Schematic Diagram

Shows the path and components of a circuit without physical layout or detail.

Location Diagram

Shows the actual physical location of each component as closely as possible.

Solenoid

An electromagnetic device with three parts: coil, plunger, and housing; shown as a circle with a label in a line diagram.

Overload Contact

A contact placed in the control circuit to protect against overcurrent: drawn in series near the coil.

Numerical Cross Reference

A system that marks each line in a line diagram with a number and notes where associated contacts appear in other lines.

Output Module

A PLC module that sends signals to field devices; classified by voltage types and current types.

Special I/O Module

A PLC module designed for specific tasks beyond standard discrete I/O.

Memory Sizing

Calculating the amount of PLC memory needed based on the number of I/O points and program complexity.

Electrical Load

A device in a circuit that consumes power; only one load allowed per line in a line diagram.

Control Device

A switch, button, or contact placed in series/parallel in a line diagram to control when a load energizes.