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Questions and Answers
What is the function key used to assign a contact number?
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?
Which symbol key is used to tie a device to the line above it on the ladder diagram?
Flow in a PLC ladder diagram must be from right to left.
Flow in a PLC ladder diagram must be from right to left.
False
Match the following input ON/OFF switching devices with their types:
Match the following input ON/OFF switching devices with their types:
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What must be inserted in slot 1 in the upper left of a PLC ladder diagram?
What must be inserted in slot 1 in the upper left of a PLC ladder diagram?
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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.
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.
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What is the purpose of a PLC?
What is the purpose of a PLC?
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Which major units are part of a PLC system?
Which major units are part of a PLC system?
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A PLC is optimized for calculation and display tasks like a computer.
A PLC is optimized for calculation and display tasks like a computer.
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The ________ is considered the 'brain' of a PLC system.
The ________ is considered the 'brain' of a PLC system.
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Match the type of memory with its characteristics:
Match the type of memory with its characteristics:
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What tasks does the input module of a PLC perform?
What tasks does the input module of a PLC perform?
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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.
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Description
This quiz covers the fundamentals of PLC systems, including programming equipment and PLC systems. It's suitable for students of electrical engineering and related fields.
