Flashcards in PLC's Deck (24)
Three applications for PLC's?
Chemical and petrochemical
Metal smelting and mining
Lumber, Pulp and Paper
Food and beverage production
The three basic components of a control system are:
PLC's are selected based on?
Number of I/O points
Smart relays are considered to be
Smaller PLC's and may have fewer than 10 I/O points
List (4) advantages of a PLC over relay control
- lower cost
PLC programs can be changed while running.
True or False?
List the major hardware components of a modular PLC system?
- power supply / clean power
- backplane / provides communication
- processor; CPU
- input/output (I/O) modules
Does the power supply for a PLC supply the field devices?
No; only the processor and I/O modules
What part of the PLC does the CPU form part of?
What is the purpose of the backplane?
Power and communication bus for the PLC components
Name three (3) types of memory used by a PLC
- RAM; random access memory
- ROM; read only memory
- EEPROM; electrically erasable programable memory
An input module _________ signals from _________ devices.
Receives signals from sensing devices
The processor is also called the ________ and is the _________.
A data highway is a type of:
A remote I/O is used to:
Reduce the amount of cabling between the PLC and I/O devices
The three (3) primary functions of a PLC processor are to:
- read and store status of all input devices
- execute user program by solving the program logic
- update the status of all the outputs
The processor carries out its functions in a sequence called a ____________ ________.
Is the signal voltage to an input module from a field device the same as the processor power supply?
No, field I/O devices require their own supply.
How is the processor input isolated from the field input signal?
By optoisolators or small relays and filter circuitry
What other problems are the processor isolated from?
- Voltage transients
- Magnetic interference that may develop in the signal circuits
What are some functions that require special I/O modules?
- position control
- high speed counters
- temp controls
- PID controls
- fuzzy logic
- ID sensors
- cam positioners
- analog I/O
Sensing devices are designed to sense what two kinds of signals?
Analog (levels of voltage or current)
Discreet (simple switches; ON or OFF)
What kind of devices can be used to program a PLC?
- small keypad
- hand held plug in keypad
- personal computer