PLC CH 2
I/O Group
A word in the output image table file and its corresponding word in the input image table file
RAM Random Access Memory
AKA Read and write memory. Designed so that information can be written into or read from the memory. Used as temporary storage of data that may need to be quickly changed.
Terminal Assembly
Attached to the front edge of the printed circuit board, is used to make the field wiring connections
Sections of a Processor Module
CPU Section and Memory Section
How bits make up one Byte
8
How words does are used in the input and output image table files
8
How are field devices classified as sinking
Field devices connected to the negative side or DC Common
Interposing Relay
For controlling larger loads and motors a standard control relay is connected to the output module. The contacts of the relay can be used to control a larger load or motor starter.
Chassis
Hardware assembly that houses I/O modules, processor modules, and power supplies. 4, 8, 12, 16 Slots
Where are the field devices connected to provide interface with the CPU?
I/O Section of the PLC
How are Field Devices classified as sourcing
If the field device is connected to the positive side of the field power supply
Current Source/ Current Sink
If the module is current sourcing module, then the input or output device must be a current sinking device, visa versa.
Bits
Individual pieces of information stored. Bits come in 1 and 0.
I1:0/0
Input, file 1, rack 0, group 0, bit 0
I1:27/17
Input, file 1, rack 2, group7, bit 17
Common devices controlled by Analog output modules
Instruments, control valves, chart recorder, electronic drives.
Address
Label or number that indicates where a certain piece of information is located in a PLC's memory. Just like your home
Examples of discrete output devices
Lights, relays, solenoids, motor starters
Analog-to-digital Converter (A/D)
Main element of an Analog module, and transitions analog signal to digital values
Volatile memory
Memory that will lose its stored information when power is lost or removed. Best to have batter backup
Discrete I/O Modules
Most common type of I/O interface modules. Connects field input devices of the ON/OFF.
EEPROM Electrically erasable programmable read-only memory
Nonvolatile that offers similar functions to RAM. Can be electronically overwritten with new data rather than be erased with UV light. Store, backup, and transfer PLC Programs
Memory Utilization
Number of memory locations required to store each type of instruction.
How many programs can be stored in memory in one time?
Only 1 program at a time
0
Open contact. Lamp that is off
Coaxial cable
Operate at distances greater than 2 miles, and is susceptible to noise from high power lines and industrial equipment.
O0:34/07
Output, File 0, Rack 3, Group 4, bit 7
O0:1/1
Output, file 0, rack 0, group 1, bit 1
Slot
Physical location of an I/O module. May be a combo of rack number and slot number when using expansion racks
What comprises a discrete output module
Power and logic section coupled by an isolation circuit
What sections comprise the input Circuit
Power section and logic Section
Field Supplied Voltage
Powers each Discreate I/O module. Can come in AC or DC
What is a module made of?
Printed Circuit board and Terminal Assembly
Analog Output Interface Module
Receives digital data from the processor, which are converted into a proportional voltage or current to control an analog field device. Accomplished by a D/A Converter
Location
Refers to an address in the CPUs memory where binary word can be stored.
Examples of Discrete input devices
Selector switches, pushbuttons, and limit switches
4 Tasks of an input Module
Sense when a signal is received from field device Convert input signal to the correct V level Isolate the PLC from fluctuations in input signal's V and A Send signal to processor which sensor originated the sensor
NPN
Sinking
PNP
Sourcing
SCADA
Supervisory Control and Data Acquisition
Purpose of Discrete Output Modules
Turn field output devices either on or off
Relay Outputs
Uses electromechanical as the switching element and can be used with either AC or DC
Remote Rack
When the rack is located away from the processor module. Uses special communications network with a unique station number.
Communications Module
links the remote racks
EPROM Erasable Programmable Read Only Memory
Provides security against unwanted changes in a program. Designed so that stored data can be read, but not easily altered without special equipment. Can only be erased with UV light. Used to backup, store, or transfer PLC programs
What do PC's require to be used as a PLC Programming terminal
Manufacturers programming software
High Density module
May have up to 64 inputs or outputs.
How do analog sensors work
Measure a varying physical quantity over a specifc range and generate a corresponding voltage or current signal. Such as temperature, speed, weight, pressure, and position
Max I/O groups in a rack
8 numbered 0-7 for up to 128 discrete I/O
What number point cards do I/O modules come in?
8,16,32,64 and the number refers to the number of inputs and outputs available
Soft PLC's
PC Based controls that use I/O card in conjuction with the PC as an interface for the field devices.
Fiber Optic Communication Table
Possible to operate up to 20 miles away with no voltage drop, and will not pick up noise from adjacent high power lines or equipment.
Reading
Process of retrieving memory
Writing
Process of storing data in memory locations
Resolution
Refers to the smallest change in input signal value that can be sensed and is based on the number of bits used in the digital representation.
Analago I/O Modules
Similar to Discrete, but these represent physical quantities that can have infinite number of values such as measuring temperature, fluid levels
Flash EEPROMS
Similar to EEPROMS in that they can only be used for backup of storage. Very fast at saving and retrieving files. Can be programmed without being removed from the processor.
Two basic types of Analog Input Modules
Voltage sensing and current Sensing
2 Types of Analog Voltage input modules
Unipolar and Bipolar
Word addressing format
Used in Analog I/O modules. Allows the entire words to be addressed
Triac Outputs
Used only for control of AC Devices
Word and Bit
Used to identify the actual terminal connection in a particular I/O module.
What types of information is stored in ROM
Used to store the programs and data that define the capabilities of the PLC
Bit oriented INputs
Each bit represents a complete information element in itself and provides the status of some external contact or advises of the presence or absence of power in a process circuit.
Nonvolatile Memory
Has the ability to retain stored information when power is removed.
Backplane
Where the modules receive their voltage, located on the rack. Typically rated for 3 A, 4 A, 12 A, 16 A
Transistor
Can be used only for control of DC Devices
Disadvantage of high density modules
Can't handle as much current per output.
1
Closed contact. Lamp that is on
Printed Circuit Board
Contains the electronic circuitry used to interface the circuit of the processor with that of the input or output device.
Output interface modules
Convert controller signals into external signals used to control the machine or process.
Type
Determines if an input or output is being addressed
Other functions of the Processor
Timing, counting, latching, comparing, motion control and complex math functions
What do HMI's give the ability to do?
To view the operation in real time.
Types of output modules
Transistor, Triac or Relay
bit addressing format
binary digit either 1 or 0. Used in Discrete I/O modules
How do Analog modules work
Accept an analog voltage or current signal form the level transmitter field device which is converted from analog to digital value for use by processor
Unipolar Modules
Accept input signal that varies from positive direction only so from 0 V to + 10 V.
Input Interface Modules
Accept signals form the machine or process devices and convert them into signals that can be used by the controller
Tag Based
Addressing scheme used in Allen-Bradley ControlLogix controllers and PC based control used in soft PLCs. Field devices are assigned a tag name that are referenced when the PLC ladder logic program is developed
Logical Rack
An addressable unit consisting of 128 input and 128 output points
What are the funcions of the Terminal Device
Enter, modify,, and troubleshoot PLC Programs. Examples are Hand Held Programmers and PC's
Rack/Slot Based
Example of addressing scheme and includes Type, slot and word and bit
ROM Read only Memory
Stores programs, and data can't be changed after the memory chip has been manufactured. Nonvolatile. Operating system is burned into the ROM and controls the system software that user uses to program PLC.
Bipolar Modules
Swing between a max negative value and max positive value such as - 10V to + 10V