Chapter 2 Flashcards
Remote rack
located away from the processor module, linked to local rack through communication module
Address
label or number that indicates where a certain piece of information is located in a PLCs memory
Two general methods to programming
- address based
- tag based (give names to each components)
Rack/slot based addressing scheme
- type: determines if input or output
- slot: physical location of I/O module
- word and slot: used to identify actual terminal connection
Tag based
- base tag: defines memory location where data is stored
- alias tag: used to create alternate name for tag
Combination I/O modules
have both input and output connections in same physical module
Standard vs high density I/O module
- standard: has 8 inputs/outputs
- high density: up to 64 inputs/outputs
Most common type of I/O interface module
- called discrete
- connects devices that require simple ON/OFF switching (example: push buttons or lights)
- classification covers bit oriented inputs and outputs (each bit represents complete information element in itself)
What is a discrete I/O module powered by
field supplied voltage source
Discrete inputs/outputs
- inputs: push buttons, selector switch, limit switch, proximity switch
- outputs:indicator lights, signaling column, relays, motor starter
Discrete input/output module circuits are composed of two basic sections
- power
- logic
sinking/sourcing
- sinking: sinking current if device receives current when on
- sourcing: sourcing current if device provides current when on
discrete devices
inputs/outputs that have only two states: on and off
analog devices
represent physical quantities that can have an infinite number of values
status indicators are good for what
troubleshooting
transducer
converts a field device’s variable into a very low level electric signal that can be amplified by a transmitter
SCP block
allows you to take an analog input from a sensor and scale it to the output units you require
processor module can be divided into two sections
- CPU: executes program and makes decisions needed to operate/communicate with other modules
- memory: stores PLC program
keyswitch has three positions
-run: executes ladder program and energizes output devices
program (prog): allows you to perform program entry and editing
-remote (rem): allows you to change processor mode from a programmer/operator interface device
why is remote mode helpful
good for online changes because you dont have to turn the machine off
memory
1 K = 1024 bytes
1 byte = 8 bits
1 word = 16 bits
contacts and binary numbers
- closed contacts have a 1 stored in respective location
- open contacts have a 0 stored in respective location
memory types
- volatile: lose stored information if all operating power is lost
- nonvolatile: will retain information if power is lost
programming terminal device
- they are needed to enter, modify and troubleshoot the program
- hand held type programmer is the simplest type
hand held programmers
-limited display capabilities
most popular method of PLC programming
to use a personal computer
major tasks in development of HMI screen
- set up communication with PLC
- create tag database
- insert graphical objects on screen
- animate objects
color displays on HMI
- green: ready, running, safe
- yellow: caution, risk of danger
- red: alarm, danger, stop
HMI
use object oriented programs, which means everything on screen is called an object
