How to Represent Machine State in Ladder Logic


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RSLogix 500 and Studio 5000 Examples

In industrial PLC programming, a machine state is a numeric value that tells the program what step or condition the machine is currently in.

Instead of …

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Advanced PLC Logic Structure: State Machines


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Building Professional and Industrial Ladder Logic with State Machines, Subroutines, and Status Codes

In a basic PLC program, it is common to organize the logic using a simple structure:

Input BufferingMode SelectionRequestsPermissivesInterlocksCommandsFault …

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Recommended PLC Logic Structure (Subroutine)


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A Simple and Professional Way to Organize Ladder Logic

In industrial PLC programming, the logic should not be written randomly. A professional PLC program is usually organized in a clear sequence …

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Faults vs Alarms in Ladder Logic: Industrial Door PLC Example


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Introduction

In industrial automation, one of the most important differences a technician must understand is the difference between a fault and an alarm.

At first, both may look similar because both indicate …

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Permissive vs Interlock in Ladder Logic


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A Critical Difference Every PLC Technician Should Understand

In industrial automation, two words are often used together but do not mean exactly the same thing:

Permissive and Interlock

Both are used to control …

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PLC Counters for Production Tracking


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Using CTU, CTD, and RES to Count Real-World Events

Counters are one of the most useful instructions in PLC programming because industrial machines are constantly counting something.

A PLC may need to …

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PLC Timers: TON, TOF, and RTO


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Understanding the Three Most Common PLC Timer Instructions

Timers are one of the most important instructions in PLC programming. They are used everywhere in industrial automation.

You will see timers used for:

Start-up …

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Start/Stop Seal-In Circuit Explained


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One of the Most Important PLC Ladder Logic Patterns

One of the first ladder logic circuits every PLC beginner should understand is the Start/Stop seal-in circuit.

This circuit is also called a:

Start/Stop …

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Sensor Debounce in Industrial Control Systems


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Filtering Noisy Inputs and Preventing Unstable PLC Logic

In industrial automation, field devices do not always send perfectly clean signals to the PLC. A sensor, limit switch, push button, or relay …

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