Automation - weeks 1/2 Flashcards
programmable logic controllers (PLCs) were first used by??
- automotive industry in late 1960s
each time the design of automobile was changed, what happened w control system operating machinery
- it was changed as well
define: PLC
- special type of computer designed to perform a special function
PLCs are designed to be programmed w what kinds of diagrams (2)?
- schematic
- ladder
PLCs and PCs employ what type of computer & memory chips?
- employ same type of computer and memory chips to perform intended tasks
PLCs must operate in industrial enviro and be able to: (4)
- withstand extremes of temp
- ignore voltage spikes and drops on power line
- survive in atmosphere containing corrosive vapors, oil, and dirt
- withstand shock and vibration
what are the basic components of PLCs (9)
- power supply
- central processing unit (CPU) –> PLC “brains”
- programming terminal
- I/O rack
- input module
- output module
- internal relays
- timers and counters
- off-delay circuit
PLC basic components:
what does the power supply do (3)
- lowers incoming AC voltage to desired level
- rectifies it to direct current
- filters and regulates
PLC basic components:
with power supply, internal logic operates on…
5 to 24 volts DC
PLC basic components:
with power supply, internal logic must be free of…
- free of voltage spikes and electrical noise
PLC basic components:
with power supply, internal logic must be regulated to…
- within 5% of required voltage value
PLC basic components:
what is a CPU
- contains microprocessor chip & related integrated circuits performing all logic functioning
PLC basic components:
CPUs have a…
- key on front panel (or software switch)
PLC basic components:
describe the purpose of the key on CPUs
- must be turned on before programming
- prevents program from being changed or deleted
PLC basic components:
with CPUs, plug connections provide….
- connection for programming terminal and I/O racks
PLC basic components:
the programming terminal programs…
- CPU
PLC basic components:
the type of programming terminal depends on… (2)
- manufacturer
- consumer
PLC basic components:
describe the purpose of small handheld devices (liquid crystal display or light-emitting diodes) on programming terminals
- show program display one line at a time or use Boolean language
PLC basic components:
describe the purpose of display & keyboard on programming terminals
- displays several lines of program and used to observe operation of circuit as it is operating
PLC basic components:
describe the purpose of notebooks (laptop) on programming terminals
- permits computer to be connected to PLC input
- software program generally available from PLC manufacturer
PLC basic components:
the programming terminal is also used to…
- troubleshoot circuit –> when terminal is connected to CPU, circuit can be examined while in operation
PLC basic components:
what is the purpose of the I/O rack
- connects CPU to outside world
- contains input modules and output modules
PLC basic components:
what is the purpose of input modules in I/O racks
- carry info from control sensor devices to CPU
PLC basic components:
what is the purpose of output modules in I/O racks
- carry instructions from CPI to output devices in field
PLC basic components:
on I/O racks, modules contains…
- contain more than one input or output
PLC basic components:
what is the I/O capacity
- as few as 16 to several hundred
PLC basic components:
what is the function of internal relays
- performs actual logic
PLC basic components:
internal relays exists only in…
- logic of computer
PLC basic components:
describe programming of internal relays (2)
- any number of contacts that can be programmed normally open or normally closed
- programmed by assigning a certain number
PLC basic components:
describe programming of timers & counters (4)
- internal relays
- programmed into logic by number
- inserted into program
- generally programmed in 0.1 sec internals or decimal key
PLC basic components:
input module - CPU of PLC
- sensitive to voltage spikes and electrical noise
PLC basic components:
with input modules, the input I/O uses…
- opto-isolation to electrically separate incoming signal from CPU
PLC basic components:
describe the metal-oxide-varistor (MOV) in input modules
- connected across AC input helps eliminate any voltage spikes
PLC basic components:
with input modules, the bridge rectifier changes…
- AC voltage into DC
PLC basic components:
with the input module, the resistor limits current to…
- LED
PLC basic components:
with light modules, light is detected by _______, which signals _______
- detected by a phototransistor, which signals CPU that voltage present at input terminal
PLC basic components:
with input modules, module has ______ input
- more than 1 input
PLC basic components:
with input module, bridge rectifiers are connected together on one side to form a ________. On the other side, rectifiers are labeled _____
- common terminal
- labelled 1,2,3, and 4