PLCs Flashcards
What is the purpose of the backplate of a PLC?
- supply power to the modules
- data communication for the modules
What are the four main components of a PLC?
Input, CPU, Programming Device, Output
What is the input section?
Designed to sense the state of the field devices that are wired to the input terminal
What are the three categories of input mm output devices?
Discrete, Analog, Pulse-generating
What are the four basic functions of the input module?
Termination, signal conditioning, isolation, indication
What is the purpose of signal conditioning in the input?
Incoming signals rectified - bridge rectifier
Noise and denounce filter
Threshold level detection
What is the purpose of the optical coupler (isolation) of the input module?
To isolate the PLC from potentially high voltages. Optocoupler can withstand very high and very low voltage differences, protecting the PLC from voltage surges
What are the two types of DC inputs?
Sinking and sourcing
What is a sinking type module?
The DC positive source is switched (ex. Limit switch) into the input terminal, negative or common source is connected to -V of the terminal
What is a sourcing type DC module?
The DC 0V source is switched into the terminal.
The DC positive source would be connected to +V
Indicate the wire colours
Blue - Negative
Brown - Positive
Black - switched output
Define Address
A character and number combination that identifies a particular and unique
area of memory
Define Analogue
A mechanism in which data is represented by continuously variable
physical quantities. A voltage or current signal that continuously changes in a smooth
gradual progression over a specific range would be an analogue signal
Define Bit
Binary digit, the smallest particle of data. A bit can have a logical value of 1 or 0
Define Bit
Binary digit, the smallest particle of data. A bit can have a logical value of 1 or 0
Define Branch
a possible alternate path for the flow of “control power flow” in ladder logic. Instructions that are placed on different branches with a common end point are said to
be “logically OR’d”
Define Data Table
An area of memory which stores the status of individual bits or groups of bits. A data table is part of a computer or PLC memory map.
Define Data Word
a group of bits: in most PLCs the word size is 16 bits.
Define Image Table
A section of the data table, associated with real (hardware) inputs and outputs.
Define MCR (CMR)
Master Control Relay. A relay used to shut off power to the I/O but not normally to the CPU
Define Software
The computer program, which PLC manufacturers sell, to allow the writing and monitoring of PLC programs.
Define Upload
To copy a PLC program from the PLC into the computer so that it can be monitored, modified, and/or documented
Define Variable
A program element associated with a hardware address or an internal memory bit
Define Alias Tag
A tag that references memory defined by another tag. An alias tag may refer to another
alias tag or a base tag. An alias tag may also refer to memory within another tag by referencing a member of a structure tag, or a bit within an integer tag or member