2 Basic Ladder Instructions R1.1

8/18/2019 2 Basic Ladder Instructions R1.1

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© 2013 Eaton Corporation. All rights reserved.

PLC Programming Basics


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2© 2013 Eaton Corporation. All rights reserved.


Basic Ladder Logic “Bit” Instructions

Set Reset One-shot Rising orFalling


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Instruction Addressing

• Input and output bit instructions are

addressed ith either actual !ph"sical#digital I$O addresses or internal storage

bit addresses%

• &hese addresses are de'ned b" the PLC


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• eas"()) controllers use “*ar+ers” ,orinternal addresses such as *). *)(.

/

• eas"()) controllers use Ixx ,or actual!ph"sical# Input addresses and Q00 ,or

Output addresses% 10ample2 I01, I08 areInputs and 3). 3)4 are Outputs


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• *ar+er addresses !*00# are internal

storage addresses de'ned b" thecontroller% &he" are used as internal

rela"s

• Real-orld Input and Output addressesmust correspond to the actual !ph"sical#

input terminal as de'ned b" the

controller


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Read real worldinputs

Evaluate

ladder

Write real worldoutputs


7/197© 2012 Eaton Corporation. All rights reserved.


Inputs

• Input instructions change state hen

poer is applied to the input terminal

ith the corresponding address

• It5s common to call the ,olloing

instruction “&rue” rather than “Closed”

hen poer is applied to the terminal its

addressed to




Inputs

• It5s also common to call the ,olloing

instruction “False” rather than “Open”

hen poer is applied to the input

terminal it5s addressed to




Outputs

• Outputs “energi6e” hen rung

conditions preceding them are “&rue”

• 7hen Input is &rue. Output is

energi6ed




Set$Reset

• A Set instruction remains &rue e8en

a,ter the rung conditions that made it

&rue become False

• A Set instruction must be accompanied

b" a Reset instruction addressed ith

the same address in order to reset thebit. based on "our logic




Set$Reset 10ample

Input sets Output and Input 9 resetsOutput !Inputs : 9 must not be &rue atthe same time#




In 1

Ladder is e8aluated !scanned#starting ,rom the top rung. le,t toright. ,olloed b" the ne0t rung.and so on. until the bottom is

reached% &hen starts again at theto %

Timer 1

Out 1

In 2 Out 2

Timer 1




Logical A/;$OR Operations

I, Input A AND Input Bare &rue. the Output ill

energi6e

I, Input A OR Input Bis true. the Output illenergi6e




A/;$OR Combination Logic

Output < is energi6ed i, A AND !B OR C#are &rue


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PLC Programming Basics - &imers

• &imers

• &o basic t"pes o, timers in PLCs2

% On-dela" timers

9% O=-dela" timers


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• On-dela" timers

7hen an On-dela" timer is energi6ed

!&rue# it delays turning On the timer5s

output bit until the timer5s preset time8alue is reached% &he output bit is

o,ten called the timer5s “;one” bit and

it indicates the timer has attained itspreset time%


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• O=-dela" timers

7hen an O=-dela" timer is energi6ed

!&rue# it immediatel" turns On its

output !;one# bit% &he timer then

delays turning Of the output !;one#

bit ,or the timer5s preset time. a,ter the

timer is de-energi6ed !False#%O=-dela" timers are less common than

On-dela" timers%


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2 Basic Ladder Instructions R1.1

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