Lec 3 - PLC Addressing and Basic Instructions PDF

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Programmable Logic Controllers PLC Addressing and Basic Instructions

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-1

Basic addressing • For the Allen-Bradley PLCs and the simulator used, the input and output image areas (in addition to other data) are held in “data files” • Each “data file” holds information such as – – – – – –

Discrete input values Discrete output values Values associated with timers Values associated with counters Status information Etc.

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-2

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PLC data files

Simulator data files

AB PLC data files

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-3

I/O memory mapping • Basic AB PLC addressing Data file type I – input O – output S – status B – binary T- timer C-counter

Slot number (not used with the simulator)

X1:x.0/0

Data file number (can be omitted for the basic data files)

Bit number

Word number: selects a specific word in a data file

I/O located on the controller (embedded I/O) is slot 0. I/O added to the controller (expansion I/O) begins with slot 1. Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-4

3-2

Example Addressing

CPU Module (slot 0)

Digital Input Module (slot 1) 16 inputs

Digital Output Module (slot 2) 8 outputs

Would occupy addresses I1:1.0/0 through I1:1.0/15

Would occupy addresses O0:2.0/0 through O0:2.0/7

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-5

Basic instructions • Examine If Closed (XIC) • Examine If Open (XIO) • • • •

Output Energize (OTE) Output Latch (OTL) Output Unlatch (OTU) One-shot Rising (OSR)

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-6

3-3

Examine if closed (XIC) • Alternate name: Normally open contact • Use the XIC instruction in your ladder program to determine if a bit is on. – When the instruction is executed, if the bit addressed is on (1), then the instruction is evaluated as TRUE. – When the instruction is executed, if the bit addressed is off (0), then the instruction is evaluated as FALSE.

Instruction symbol

Normally open switch is open

Normally open switch is closed Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-7

Examine if open (XIO) • Alternate name: Normally closed contact • Use the XIO instruction in your ladder program to determine if a bit is off. – When the instruction is executed, if the bit addressed is on (1), then the instruction is evaluated as FALSE. – When the instruction is executed, if the bit addressed is off (0), then the instruction is evaluated as TRUE.

Instruction symbol Normally open switch is open

An XIO instruction inverts the state of the bit it references. Electrical & Computer Engineering

Normally open switch is closed

Dr. D. J. Jackson Lecture 3-8

3-4

Output energize (OTE) • Alternate name: coil • This instruction is usually used in conjunction with XIC or XIO or any other input instruction. • If the logic preceding the OTE instruction is true (1), the OTE instruction will be energized Not energized

Instruction symbol

An OTE instruction can only be the last instruction on a rung. Electrical & Computer Engineering

Energized Dr. D. J. Jackson Lecture 3-9

Output latch (OTL) • The OTL instruction is used only to turn a bit on and latch it on Initially not energized

Instruction symbol Energized

L Latched

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-10

3-5

Output unlatch (OTU) • The OTU instruction is used only to turn a bit off and latch it off • OTL and OTU are generally used in pairs Instruction symbol

U

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-11

One-shot rising (OSR) • When the rung conditions preceding the OSR go from false-totrue, the OSR instruction goes true also but for only one scan • The address on the OSR instruction is a bit that is used to reflect the state of the input to the OSR.

Instruction symbol OSR

I:1/0 OSR output One PLC scan

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-12

3-6

Branches • Branches can be inserted in ladder logic programs to create parallel combinations of various ladder logic elements

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-13

Multiple Series/Parallel Branches • Multiple series/parallel branches can be utilized with multiple inputs and also affecting multiple outputs in parallel

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-14

3-7

PLC simulator usage • Ladder logic elements (instructions) can be dragged and dropped onto the ladder window to create a ladder logic program • The ladder logic program is executed by going online, ‘downloading’ the PLC program, and switching to run mode

OFFLINE/ONLINE control

Download

Electrical & Computer Engineering

PLC run mode Dr. D. J. Jackson Lecture 3-15

ProSim simulations • The Logixpro simulator provides a set of built-in simulations • The I/O simulation initially will be of most use since it provides access to simulated discrete inputs (switches) and outputs (lamps)

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-16

3-8

Other Prosim simulations • Available simulators – – – – –

Door simulator Silo simulator Traffic simulator Batch simulator Dual Compressor simulator

– Bottle line simulator – Four floor elevator simulator

• Most projects will involve designing ladder logic programs to control these simulations Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-17

Batch simulator showing example I/O

Electrical & Computer Engineering

Dr. D. J. Jackson Lecture 3-18

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