PLC CH 2

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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


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