PLC Basics Quiz

12 Questions

What is the function key used to assign a contact number?

Which symbol key is used to tie a device to the line above it on the ladder diagram?

Vertical connection symbol

Flow in a PLC ladder diagram must be from right to left.

False

Match the following input ON/OFF switching devices with their types:

Toggle-type Switches = A-G Push button Switches = H-K Limit Switches = SPST - Single Pole Single Throw

What must be inserted in slot 1 in the upper left of a PLC ladder diagram?

A contact

The total time for one complete program scan is a function of processor speed and length of user program, divided into INPUT SCAN, PROGRAM SCAN, and __________ SCAN.

OUTPUT

What is the purpose of a PLC?

To monitor crucial process parameters and adjust process operation accordingly.

Which major units are part of a PLC system?

Central Processing Unit (CPU)

A PLC is optimized for calculation and display tasks like a computer.

False

The ________ is considered the 'brain' of a PLC system.

Central Processing Unit (CPU)

Match the type of memory with its characteristics:

ROM = Fixed operating memory RAM = User Program PROM = User Program EPROM = User Program, Erasable by UV Light EEPROM = User Program, Erasable by Electrical Signals NOVRAM = User Program, Erasable by Electrical Signals

What tasks does the input module of a PLC perform?

Sensing input signals, converting them for electronic circuits, providing isolation, and producing an output signal.

Study Notes

PLC Basics

A PLC (Programmable Logic Controller) is a user-friendly, microprocessor-based computer that performs control functions of various complexities.
It monitors crucial process parameters and adjusts process operations accordingly.
PLCs can operate with discrete (on/off) or analog (variable) outputs and inputs.

History of PLC

PLCs were introduced in the late 1960s.
The first commercial PLC was designed by Modicon as a relay replacer for General Motors.
Early PLCs had thousands of electronic parts, but with the advent of microprocessors in the late 1970s, they evolved into sophisticated systems.

Differences between PLC and Computer

A computer is optimized for calculation and display tasks, while a PLC is designed for control and regulation tasks.
A computer is programmed by specialists, whereas a PLC is programmed by non-specialists.
PLCs are adapted to industrial environments.

Advantages and Disadvantages of PLC

Advantages: newer technology, fixed program applications, environmental considerations, fail-safe operation, and fixed circuit operation.
Disadvantages: not mentioned explicitly.

PLC System Layout and Connection

A PLC system consists of four major units: Central Processing Unit (CPU), Programmer/Monitor, I/O Modules, and Racks and Chassis.
The CPU is the "brain" of the system, consisting of a microprocessor, memory, and power supply.
The Programmer/Monitor is a device used to communicate with the PLC circuits.
I/O Modules have input and output terminals for connecting to sensors, transducers, and output devices.
Racks and Chassis provide mounting and enclosures for the PLC parts.

CPU Components

The CPU consists of a microprocessor, memory, and power supply.
Fixed Memory contains the program set by the manufacturer and is non-erasable.
Alterable Memory contains user programs and is stored in RAM chips.
The processor section carries out arithmetic and logic operations.

Input and Output Modules

Input Modules perform four tasks: sense input signals, convert signals to DC levels, electronically isolate the input module output, and produce an output for the CPU.
Output Modules operate in the opposite manner, converting DC signals from the CPU to usable output voltages.

Power Supplies

PLCs operate on +5 and -5 volts DC, which are converted from the 120-volt AC input.
The power supply consists of an AC conditioning block, converter/rectifier, filter section, and regulator.

Programming Equipment

Programming equipment includes hand-held, full-sized, and software-based programmer/monitors.
Programming formats vary between devices, with different nomenclature, numbering schemes, and screen appearances.

PLC Scanning

Each PLC operational cycle consists of three parts: input scan, program scan, and output scan.
The total time for one complete program scan depends on processor speed and program length.

Input Devices

Various types of ON/OFF switches can be connected to PLC input modules, including toggle-type switches, push-button switches, limit switches, and others.
Analog devices, such as potentiometers, linear variable differential transformers, and thermocouples, can also be used as input devices.