Chapter 1- Overview Flashcards
What is a PLC?
A programmable logic controller is a device that can be programmed to perform a control function.
What are the components of a PLC?
Programming terminal, Input interface, CPU, Memory, Output interface, Power Supply
What is a programming terminal?
A device that allows the user to add, delete or modify programs in the PLC’s memory
What is a program?
A representation of the actions required to produce the correct output control signals for a given process
What is an input interface?
Receives and convert field signals in analog or digital signals that the CPU can interpret
What is the CPU?
The central processing unit takes the input signals it receives, selects the proper program from the memory and sets the output signal, which instructs the output on which control action to perform
What is the output interface?
Takes the signal it receives from the CPU and produces the appropriate control action.
What is the memory?
The memory stores the user programs and other data
What is the power supply?
The power supply provides all the voltage levels needed to operate the PLC by converting AC into DC voltage
What are the IEC 61131-3 programming languages?
Ladder logic (ladder diagrams) Flowchart (function block diagram) Structured Text Instruction List Sequential Function Chart
What is the most common PLC programming language?
Ladder Logic- an advanced form of relay logic, that incorporates Boolean principles. It allows the user to specify contact closure types and coils. Allows the entry of math functions, analog control, complex counter and timing operations.
What is a digital signal?
A binary signal that is either 1 or 0, on or off, true or false. Each single signal is a bit, which can form working groups called words. Represented with a square wave.
What is an analog signal?
Analog signals interpret different levels of signals, and are represented with a sine wave.
How are analog signals created?
Analog signals are produced using transducers. Transducers convert a physical quantity into electric signals by measuring the physical quantity of a substance and altering the voltage or current supply proportionately. The conversion rate isn’t 1:1. Programming software is used to scale the raw voltage and convert it into meaningful measurement. Ex. A 2 degree increase in temperature equates to a 100mps increase.
What does AC stand for?
Alternating Current- voltage that can be carried long distance over wires. Ex. Power company lines
