Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Search
  • Books
  • Software
  • Projects
  • Process
  • Tools
  • Basics
  • Formula
  • Power Plant
  • Root Cause Analysis
  • Electrical Basics
  • Animation
  • Standards
  • 4-20 mA Course
  • Siemens PLC Course
Reading: Comparison Instructions in PLC Programming
Share
Notification Show More
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • Design
  • PLC
  • Interview
  • Control System
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > PLC Tutorials > Comparison Instructions in PLC Programming

Comparison Instructions in PLC Programming

Last updated: March 4, 2021 3:11 pm
Editorial Staff
PLC Tutorials
2 Comments
Share
6 Min Read
SHARE

Comparison instructions in PLC are used to test pairs of values to condition the logical continuity of a rung.

Contents
Types of Comparison InstructionsEqual (EQU) InstructionNot Equal (NEQ) InstructionLess Than (LES) InstructionLess Than or Equal (LEQ) InstructionGreater Than (GRT) InstructionGreater Than Or Equal (GEQ) InstructionMasked Comparison for Equal (MEQ)Limit Test (LIM) InstructionTrue/False Status of the LIM Instruction

Thus, comparison instructions would seldom, if ever, be the last instruction on a rung.

Types of Comparison Instructions

Types of Comparison Instructions in PLC

As an example, suppose a LES instruction is presented with two values. If the first value is less than the second, then the comparison instruction is true.

Equal (EQU) Instruction

Equal (EQU) Instruction in PLC Programming

Use the EQU instruction to test whether two values are equal. If source A and source B are equal, the instruction is logically true. If these values are not equal, the instruction is logically false.

Source A must be an address.

Source B can be either a program constant or an address.

Values are stored in two’s complementary form.

Not Equal (NEQ) Instruction

Not Equal (NEQ) Instruction in PLC Programming

Use the NEQ instruction to test whether two values are not equal.

If source A and source B are not equal, the instruction is logically true.

Source A must be an address.

Source B can be either a program constant or an address.

Values are stored in two’s complementary form.

Less Than (LES) Instruction

Less Than (LES) Instruction in PLC Programming

Use the LES instruction to test whether one value (source A) is less than another (source B).

If source A is less than the value at source B, the instruction is logically true.

Source A must be an address.

Source B can be either a program constant or an address.

Values are stored in two’s complementary form.

Less Than or Equal (LEQ) Instruction

Less Than or Equal (LEQ) Instruction in PLC Programming

Use the LEQ instruction to test whether one value (source A) is less than or equal to another (source B).

If the value at source A is less than or equal to the value at source B, the instruction is logically true.

Source A must be an address.

Source B can be either a program constant or an address.

Values are stored in two’s complementary form.

Greater Than (GRT) Instruction

Greater Than (GRT) Instruction in PLC Programming

Use the GRT instruction to test whether one value (source A) is greater than another (source B).

If the value at source A is greater than the value at source B, the instruction is logically true.

Greater Than Or Equal (GEQ) Instruction

Greater Than Or Equal (GEQ) Instruction in PLC Programming

Use the GEQ instruction to test whether one value (source A) is greater than or equal to another (source B).

If the value at source A is greater than or equal to the value at source B, the instruction is logically true.

Masked Comparison for Equal (MEQ)

Masked Comparison for Equal (MEQ) Instruction in PLC Programming

Use the MEQ instruction to compare data at a source address with data at a compare address.

The Use of this instruction allows portions of the data to be masked by a separate word.

Source is the address of the value you want to compare.

Mask is the address of the mask through which the instruction moves data.

The mask can be a hexadecimal value.

Compare is an integer value or the address of the reference.

If the 16 bits of data at the source address are equal to the 16 bits of data at the compare address (less masked bits), the instruction is true.

The instruction becomes false as soon as it detects a mismatch.

Limit Test (LIM) Instruction

Limit Test (LIM) Instruction in PLC Programming

Use the LIM instruction to test for values within or outside a specified range, depending on how you set the limits.

The Low Limit, Test, and High Limit values can be word addresses or constants, restricted to the following combinations:

  • If the Test parameter is a program constant, both the Low Limit and High Limit parameters must be word addresses.
  • If the Test parameter is a word address, the Low Limit and High Limit parameters can be either a program constant or a word address.

True/False Status of the LIM Instruction

If the Low Limit has a value equal to or less than the High Limit, the instruction is true when the Test value is between the limits or is equal to either limit.

Status of the LIM Instruction

If the Low Limit has a value greater than the High Limit, the instruction is false when the Test value is between the limits.

Limit Test (LIM) Status

If you liked this article, then please subscribe to our YouTube Channel for PLC and SCADA video tutorials.

You can also follow us on Facebook and Twitter to receive daily updates.

Read Next:

JUMP Instruction in PLC Programs

Master Control Reset (MCR) in PLC

One Shot Rising & Falling Instructions

Sequence and Logic Control in PLC

Scaling with Parameters Instruction

Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

Free Download Programmable Logic Controller (PLC) Book
RSLogix5000 PLC Program Backup procedure
PLC Data Comparison Instructions
Download Allen Bradley RSLogix PLC Software
Electric Motor Forward Reverse with Repeat Cycle PLC Logic
4-20mA Loop Power Supply Questions and Answers
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
2 Comments
  • Romel Roy says:
    September 4, 2019 at 8:14 pm

    Dear Sir
    This is the fantastic Documents for Study & Learning you have given.
    Indeed there are lots of lessons to learn.
    Kindly, keep on teaching us so that we can upgrade the human civilization.
    With Regards

    Reply
  • Florencio says:
    September 17, 2019 at 3:28 am

    The logical instructional tools will help us greatly in developing our skills between PLC and SCADA …

    keep providing these tools

    graciously

    Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
210kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

Step by Step Guidelines for Downloading Free PLC software
PLC Multiple Choice Questions
Various Causes for PLC Going in Stop Mode
PID Block in RSLogix 500
Chemical Mixing Process using PLC
Siemens S7 300 CPU Status and LED Errors Explanation
Top PLC Manufacturers
PLC Motor Control Ladder Logic Programming

Keep Learning

Use of Isolators and Barriers in Electrical Panel

Use of Isolators and Barriers in Electrical Panel

Open Platform Communication (OPC)

Open Platform Communication (OPC)

Allen-Bradley PLC

#15 PLC Best Practices – Safe State when PLC Restarts

PLC Program to Drain Same Products from Two Tanks

PLC Program to Drain Same Products from Two Tanks

3 to 8 Line Decoder Circuit Diagram

3 to 8 Line Decoder PLC Ladder Diagram

Structured Text in PLC: Parking Information Systems

Structured Text in PLC: Parking Information Systems

Functional Block Diagram PLC Example for Traffic Light System

Functional Block Diagram PLC Example for Traffic Light System

DCS Alarm and Setpoint

Setpoints and Alarms in Control System

Learn More

Data Instance in PLC

Tia Portal – Different Instances of Calling a Function Block

Digital Electronics Multiple Choice Questions

Half Adder and Full Adder Objective Questions

Process Safety and Instrumentation

Process Safety and Instrumentation

Simatic 300 Station Configuration

Monitor and Modify Variables in Simatic Manager

Orifice Plate Flow Requirements

What are the Orifice Plate Flow Requirements?

PID Controller Tunning Manually

PID Controller Parameters Tuning Manually

Proof Testing of Safety Instrumented Systems

Proof Testing of Safety Instrumented Systems

Electrical Machines Questions and Answers

MCQ on Rotating Electrical Machines

Menu

  • About
  • Privacy Policy
  • Copyright

Quick Links

  • Learn PLC
  • Helping Hand
  • Part Time Job

YouTube Subscribe

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?