30 Questions
What is the primary computer platform used in industrial control and automation applications?
Programmable logic controllers (PLCs)
Why were PLCs developed?
To provide flexibility in changing control logic
What industry's need led to the development of PLCs?
Automotive industry
What was the problem with hard-wired relay logic panels in the automotive industry?
They were inflexible for changing control logic
What was the desired change in the logic of I/O devices that led to the development of PLCs?
Soft-wiring instead of hard-wiring
What did PLCs replace in automated factories?
Hard-wired relay logic panels
How are the logic functions AND and OR implemented in ladder logic diagrams?
AND is implemented by series connections, and OR is implemented by parallel connections
Which of the following is a standard logic in a ladder logic diagram (LLD)?
Seal-in circuit
What is the purpose of a software drum in PLC programs?
It is the software analog of a mechanical cam, actuating an output line based on the input cam shaft position
How is the NOT function implemented in ladder logic diagrams?
By a cross over the contact signal
What is the benefit of a software drum compared to a mechanical drum?
It is programmable
How are the discrete input channel state and the discrete output channel state represented in ladder logic diagrams?
Discrete input channel state is represented by two vertical lines, and discrete output channel state is represented as a circular symbol
What type of memory can PLC memory be?
ROM
How many discrete I/Os can a PLC with 3 racks, 12 slots, and 16 discrete I/O in each slot support?
576 discrete I/Os
What is the maximum number of slots a PLC rack can have?
15 slots
What is the purpose of timer and counter modules in PLCs?
Pulse counting and event timing
How are I/O data associated with the modules in a PLC?
Memory mapped to the CPU's address space
What type of interface is a standard hardware interface for I/O modules in PLCs?
Key asset
What are the three main programming languages supported by PLCs?
Ladder logic diagrams (LLD), Boolean language, and Flowchart language
Why is Ladder logic diagrams (LLD) the most widely used language in PLCs?
Due to its similarity to hardware relay logic diagrams and field technicians' familiarity
How do PLCs execute programs?
In scan mode, scanning the entire program logic every scan period
What does PLC ladder logic focus on?
Industrial control and logic, supporting typical data structures like bits, bytes, words, and characters
How are I/O devices connected to a common communication bus in PLCs?
Using a T-type connector, reducing wiring between the device and the PLC
What type of map exists between I/O points on the hardware and CPU memory addresses in PLCs?
One-to-one map
What is the typical software development tool for PLCs?
Notebook PC, communication interface, and software development environment
What are the various I/O units supported by virtually every PLC platform?
Digital input/output, analog input/output, high speed counter and timer, and communication modules
How are PLCs mostly programmed?
Using ladder logic diagrams
What is the real trend in industrial control according to the text?
Complementary use of PLCs and PC-based control
What does the PLC hardware design include?
Backplane carrying power and communication bus, with slots forming the electrical interface between I/O modules and the bus
Why do PLCs continue to be strong in the market?
Due to their modular design and ruggedness
Study Notes
Industrial Control Systems: PLCs and PC-based Control
- PLCs are widely used for large scale networking via the internet between factory PLCs and enterprise level computers.
- PLCs have a standardized rack-mounted physical shape with slots for I/O interface units and support multiple I/O racks.
- Typical software development tools for PLCs include a notebook PC, communication interface, and software development environment.
- PLCs are categorized into three to four major sizes based on I/O capabilities, CPU speed, and program functions.
- Various I/O units supported by virtually every PLC platform include digital input/output, analog input/output, high speed counter and timer, and communication modules.
- I/O modules occupy memory space in the PLC, with memory mapping used for the PLC's application program logic.
- PLCs have a modular design, rugged for harsh industrial environments, and are mostly programmed using ladder logic diagrams.
- The real trend in industrial control is the complementary use of PLCs and PC-based control, with PCs used for networking, user interface, and control logic implementation.
- PLC hardware design is based on a backplane carrying power and communication bus, with slots forming the electrical interface between I/O modules and the bus.
- The bus consists of power lines, address lines, data lines, and control lines, with the real-time kernel and user program stored in the memory.
- Claims of PLCs being replaced by PC-based control have not materialized, as PLCs continue to be strong in the market due to their modular design and ruggedness.
- The complementary use of PLCs and PCs in industrial control is the observed trend, with PCs implementing control logic and PLCs providing the I/O interface.
Test your knowledge of Industrial Control Systems with this quiz on PLCs and PC-based control. Explore topics such as PLC hardware design, software development tools, I/O modules, and the complementary use of PLCs and PCs in industrial control.
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