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Inst Tools > Blog > PLC Tutorials > Comparator in PLC Programming

Comparator in PLC Programming

Last updated: March 4, 2021 3:29 pm
Editorial Staff
PLC Tutorials
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To study the working of comparator blocks (EQU, NEQ, LES, GRT, LEQ and GEQ) using simple example in Allen Bradley programmable logic controllers (PLC).

Contents
Ccomparator in PLCDescription of Comparator Blocks :Program LogicPLC Input Output ListPLC Comparator ProgrammingLogic Description:Conclusion

Ccomparator in PLC

Ccomparator in PLC Programming

There are two parameter in each block,

Source A & Source B –where values are stored.

Description of Comparator Blocks :

EQU :

Ā Equal block is used to compare the two values stored in Source A and source B and gives output as ā€œ1ā€ if both are equal and ā€œ0ā€ if both are not equal.

LES :

Lesser than block is used to compare the two values stored in Source A and source B and gives output as ā€œ1ā€ ifĀ  Source A value is Lesser than Source B value and ā€œ0ā€ if Source A value is greaterĀ  thanĀ  or equal to Source B value.

LEQ :

Lesser than or equal toĀ Ā  block is used to compare the two values stored in Source A and source B and gives output as ā€œ1ā€ if Source A value is lesser than or equal value to Source B value and ā€œ0ā€ if Source A value is greater Source B value.

NEQ :

Not equalĀ  block is used to compare the two values stored in Source A and source B and gives output as ā€œ1ā€ ifĀ  Source A value is not same asĀ  Source B value and ā€œ0ā€ if Source A value is same as Source B value.

GRT :

Greater thanĀ  block is used to compare the two values stored in Source A and source B and gives output as ā€œ1ā€ ifĀ  Source A value is Greater than Source B value and ā€œ0ā€ if Source A value is lesser thanĀ  or equal to Source B value.

GEQ :

Greater than or equal toĀ  block is used to compare the two values stored in Source A and source B and gives output as ā€œ1ā€ if Source A value is Greater than or equal value to Source B value and ā€œ0ā€ if Source A value is Lesser Source B value.

Let us understand the working of comparator block using simple example,

Program Logic

When start switch is pressed,

  1. If water level is below 5, motor should turn ON till water level reach 95.
  2. If water level indicates the value below 5, low level water alarm should ON.
  3. If water level indicates the value above 95, high level water alarm should ON.
  4. If water level is exactly at 95, steamer should turn ON.
  5. System under control indication should always ON when water level is not equal to 100.

PLC Input Output List

PLC input output list for water tank

PLC Comparator Programming

PLC Programming Comparator examples

Logic Description:

RUNG 0000

When Start switch is pressed,N7:0 is the water level value which is compared with 5 and 95 using GEQ and LEQ block to turn ON Motor.(i.e-Motor should turn ON if water level is between 5 and 95)

RUNG 0001

Low level alarm is triggered, when water level goes below 5.Less than block is used to perform this function.

RUNG 0002

High level alarm is triggered, when water level goes above 95.Greater than (GRT) block is used to perform this function.

RUNG 0003

Steamer output is turned ON when water level reached exactly at 95.

RUNG 0004

System under control output always in ON condition when water level is not at 100.

Conclusion

We can use this example program to understand the working comparator block function in Allen Bradley programmable logic controllers (PLC).

Author :Ā Hema Sundaresan

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