PLC Revision Flashcards
What does PLC stand for?
Programmable logic controller
What is a PLC?
Specialized computer used to control machines and automated processes
How does the PLC work?
It operates by connecting inputs, outputs and networks, agreed the inputs to execute pre-programmed logic based on its state, and controls the outputs
What is the purpose of its programmable memory?
To store instructions and specific functions such as on off control, timing, counting, sequencing, arithmetic, and data handling
What type of application needs a PLC?
An application that has a need for some type of electrical control
What is the difference between PLCs and computers?
POE’s have been designed for extended temperature ranges, dirty or dusty conditions,
Immunity to electrical noise and resistance to vibration and impact .
Where are the programs to control the machine operation stored?
In the battery-backed or read only memory
What makes the PLC aerial time system?
The fact that the output results must be generated in response to the input conditions within a restricted time
The plc responds to input, with in a strict time constraint 
When will the PLC’s first introduced?
In the late 1960s
1968 to be exact
What were the control systems back then what did they consist of?
Consisted of hardwire panels containing multiple relays and associated interwiring.
what were the traditional control systems disadvantages?
Time consuming.
Costly to wire debug change and maintain
What was the primary reason for designing a PLC?
To eliminate large cost involved with replacing the complicated relay based machine control systems.
Who is sued the request for the PLC and why?
GM Hydramatic The hardwired release system with an electronic replacement
Who won the proposal?
Bedford associates of Boston, Massachusetts.
Who did Bedford associates branch of to and what did they call their first PLC
Modicon was their first PLC which stood for modular digital controller.
Who was considered the father of PLLC’s?
Dick Morley
Who was responsible for creating the first software PLC
Host engineering who created the first Windows based plc
What’s the requirements for computer controllers when they were first being invented?
Solid state not mechanical
Easy to modify input and output devices
Easily programmed and maintained by plant electricians
Be able to function in an industrial environment
The first PLC is had no hard drive but they had
Battery back up
What was characteristics of the first plc
Programmable, reusable and reliable
could withstand harshindustrial environment.
Used ladder logic
could start in seconds
Battery backed
What are the advantages of PLC control systems?
Flexible
Handles more complicated systems
Faster, response time line
less and simpler wiring
Modular design making it easy to repair an expanded
Solid state no moving parts
Expensive
easy to troubleshoot
What are the four important steps in PLC operation?
Check input status
Execute program
Diagnostic/communications
Updates output status
Explain the first step of PLC operation
Check input status
Plc examines all inputs determines if they are on or off and records this status for the next step
Explain the second step of the PLC operation
Execute the program
The Plc executes the program, one instruction at a time using the inputs data from the previous step and then decides what happens to the outputs and stores these execution results for later use
