PLC Programming Examples: Practical Industrial Applications Guide

Introduction: Learn Through Real-World Programming Examples

Learning PLC programming through practical examples accelerates your understanding and builds the hands-on experience needed for successful industrial automation careers. This comprehensive guide presents real-world programming examples that demonstrate essential techniques, best practices, and problem-solving approaches used by professional automation engineers.

Each example in this guide progresses from simple concepts to more complex applications, building your skills systematically while demonstrating how fundamental programming principles apply to actual industrial control problems. These aren't theoretical exercises – they represent the types of control challenges you'll encounter in manufacturing facilities worldwide.

The examples cover diverse industrial applications including motor control, conveyor systems, batch processing, temperature control, and safety systems. Each example includes complete ladder logic code, detailed explanations of the programming techniques used, and practical implementation tips that help you apply these concepts to your own projects.

By studying and practicing with these examples, you'll develop the pattern recognition and problem-solving skills that distinguish experienced PLC programmers from beginners. These examples provide templates and techniques you can adapt for your own applications while demonstrating professional programming standards and documentation practices.

Chapter 1: Basic Motor Control Examples

Simple Start/Stop Motor Control

This fundamental example demonstrates the basic principles used in virtually all industrial motor control applications. The program includes a start button, stop button, and motor starter contactor with auxiliary contact feedback for maintaining the circuit after the operator releases the start button.

```

Rung 0000: Motor Start/Stop Control

|----] [----------] [----------]/[----------( )-------|

Start_PB Stop_PB E_Stop Motor_Run

I:0/0 I:0/1 I:0/2 O:0/0

|----] [---------------------------------------------|

Motor_Run_Aux

I:0/3

```

The program logic creates a seal-in circuit where pressing the Start button (I:0/0) energizes the Motor_Run output (O:0/0), which controls the motor starter contactor. The auxiliary contact from the motor starter (I:0/3) creates a parallel path that maintains the circuit after the start button is released.

The Stop button (I:0/1) and Emergency Stop (I:0/2) are wired as normally closed contacts in series with the motor circuit. When either button is pressed, it opens the circuit and stops the motor. This configuration provides fail-safe operation where broken wires or component failures result in motor shutdown.

This basic pattern appears in countless industrial applications with variations for specific requirements. Understanding this fundamental circuit thoroughly enables you to tackle more complex motor control applications with confidence.

Multiple Motor Sequencing

Industrial processes often require multiple motors to start and stop in specific sequences with delays between operations. This example demonstrates how to sequence three conveyor motors with appropriate time delays to prevent mechanical stress and power supply overloading.

```

Rung 0000: System Start/Stop Control

|----] [----------]/[----------] [----------( )-------|

System_Start System_Stop E_Stop System_Run

I:0/0 I:0/1 I:0/2 B3:0/0

|----] [---------------------------------------------|

System_Run

B3:0/0

Rung 0001: Motor 1 Timer Control

|----] [----------] [---------------------(TON)------|

System_Run Motor_1_Run T4:0

B3:0/0 O:0/0 Timer ON

Preset: 20

Accum: 0

Rung 0002: Motor 1 Control

|----] [----------]/[----------] [----------( )-------|

System_Run Motor_1_OL T4:0/DN Motor_1_Run

B3:0/0 I:0/10 T4:0/DN O:0/0

Rung 0003: Motor 2 Timer Control

|----] [----------] [---------------------(TON)------|

Motor_1_Run Motor_2_Run T4:1

O:0/0 O:0/1 Timer ON

Preset: 50

Accum: 0

Rung 0004: Motor 2 Control

|----] [----------]/[----------] [----------( )-------|

T4:0/DN Motor_2_OL T4:1/DN Motor_2_Run

I:0/11 O:0/1

```

This sequencing logic ensures that Motor 1 starts immediately when the system is enabled, Motor 2 starts 2 seconds after Motor 1 is confirmed running, and Motor 3 starts 5 seconds after Motor 2 is confirmed running. The delays prevent excessive power draw during startup while ensuring proper material flow.

Each motor includes overload protection monitoring and will stop the entire sequence if an overload occurs. This protective strategy prevents damage to downstream equipment and materials while providing clear indication of the fault location.

Variable Frequency Drive Control

Modern motor control increasingly uses Variable Frequency Drives (VFDs) for energy efficiency and precise speed control. This example demonstrates PLC control of a VFD including speed reference, start/stop commands, and status monitoring.

```

Rung 0000: VFD Enable Control

|----] [----------]/[----------] [----------( )-------|

VFD_Start VFD_Stop E_Stop VFD_Enable

I:0/0 I:0/1 I:0/2 O:0/0

|----] [---------------------------------------------|

VFD_Running

I:0/10

Rung 0001: Speed Reference Calculation

|----] [---------------------------------(MOV)------|

Speed_Auto Speed_Setpoint_Auto MOVE

B3:0/1 N7:0 Source: N7:0

Dest: N7:2

|----] [---------------------------------(MOV)------|

Speed_Manual Speed_Setpoint_Manual MOVE

B3:0/2 N7:1 Source: N7:1

Dest: N7:2

Rung 0002: Analog Output Scaling

|----] [---------------------------------(SCL)------|

VFD_Enable SCALE

O:0/0 Source: N7:2

Rate: 163

Offset: 6554

Dest: O:1/0

```

The program provides both automatic and manual speed control modes with a calculated speed reference sent to the VFD through an analog output. The scaling function converts the internal speed value (0-1800 RPM) to the 4-20mA signal range required by the VFD.

Status monitoring includes VFD running confirmation, fault monitoring, and actual speed feedback for process control and operator displays. This bidirectional communication enables sophisticated control strategies and comprehensive diagnostics.

Chapter 2: Conveyor and Material Handling Examples

Basic Conveyor Control with Interlocks

Conveyor systems require careful attention to safety interlocks, proper sequencing, and jam detection. This example demonstrates a typical conveyor control system with upstream/downstream coordination and safety features.

```

Rung 0000: Conveyor Permissive Logic

|----] [----------]/[----------] [----------] [----+---|

Conv_Start Conv_Stop E_Stop Guard_OK |

I:0/0 I:0/1 I:0/2 I:0/10 |

|

|----] [------------------------------------------+---|

Conv_Running |

I:0/11 |

|

|-------------------------------------------------( )|

Conv_Enable |

B3:0/0 |

Rung 0001: Jam Detection Timer

|----] [----------]/[----------(TON)----------------|

Conv_Enable Photo_Eye T4:0

B3:0/0 I:0/12 Timer ON

Preset: 100

Accum: 0

Rung 0002: Conveyor Motor Control

|----] [----------]/[----------] [----------( )-----|

Conv_Enable Conv_Jam T4:0/DN Conv_Run

B3:0/0 B3:0/1 O:0/0

Rung 0003: Jam Alarm Logic

|----] [-----------------------------------( )-----|

T4:0/DN Conv_Jam

B3:0/1

```

The conveyor includes comprehensive safety interlocks preventing operation with the guard removed, emergency stop activated, or jam conditions detected. The jam detection logic uses a photo eye to monitor material flow with a timer that triggers an alarm if no material passes for 10 seconds during operation.

Upstream and downstream coordination ensures that conveyors start in the proper sequence to prevent material backup and stop in reverse order to clear all material from the system. This coordination is essential for continuous material flow systems.

Sorting Conveyor with Diverter Control

Automated sorting systems use sensors to identify products and diverters to route them to appropriate destinations. This example demonstrates the timing and coordination required for accurate sorting operations.

```

Rung 0000: Product Detection and Classification

|----] [-----------------------------------( )-----|

Product_Sensor Product_Detected

I:0/0 B3:0/0

|----] [----------] [-------------------( )--------|

Product_Detected Type_A_Sensor Product_Type_A

B3:0/0 I:0/1 B3:0/1

|----] [----------] [-------------------( )--------|

Product_Detected Type_B_Sensor Product_Type_B

B3:0/0 I:0/2 B3:0/2

Rung 0001: Transport Delay Timer

|----] [----------]/[-----------(TON)-------------|

Product_Detected Divert_Timer_DN T4:0

B3:0/0 T4:0/DN Timer ON

Preset: 75

Accum: 0

Rung 0002: Diverter Control for Type A

|----] [----------] [----------] [-------( )-----|

Product_Type_A T4:0/DN Divert_Enable Divert_A

B3:0/1 B3:0/10 O:0/0

Rung 0003: Diverter Reset Timer

|----] [-------------------------(TON)-----------|

Divert_A T4:1

O:0/0 Timer ON

Preset: 30

Accum: 0

Rung 0004: Diverter Reset

|----]/[-----------------------------------( )---|

T4:1/DN Divert_Enable

B3:0/10

```

The sorting logic detects products, classifies them by type, calculates the transport delay to the diverter position, and activates the appropriate diverter at precisely the right time. Accurate timing is critical for reliable sorting performance.

The system includes diagnostic features for monitoring sort accuracy, tracking production counts by product type, and detecting missed sorts that require operator attention or system adjustment.

Accumulating Conveyor Control

Accumulating conveyors allow products to queue up when downstream processes are busy while preventing product damage through zone control. This example demonstrates the pressure control and zone management required for accumulating systems.

```

Rung 0000: Zone 1 Control Logic

|----] [----------]/[----------]/[---------( )----|

Conv_Enable Zone1_Full Zone1_Stop Zone1_Run

B3:0/0 I:0/10 B3:0/10 O:0/0

Rung 0001: Zone 1 Pressure Control

|----] [----------] [----------(TON)-------------|

Zone1_Run Zone1_PE T4:0

O:0/0 I:0/11 Timer ON

Preset: 20

Accum: 0

|----] [----------] [----------]/[-------( )----|

Zone1_Run T4:0/DN Zone1_Full Zone1_Stop

O:0/0 I:0/10 B3:0/10

Rung 0002: Zone 2 Control Logic

|----] [----------]/[----------]/[---------( )----|

Zone1_Full Zone2_Full Zone2_Stop Zone2_Run

I:0/10 I:0/20 B3:0/11 O:0/1

Rung 0003: Downstream Release Control

|----] [----------]/[----------]/[---------( )----|

Downstream_Ready Zone3_Full Release_Stop Release_Run

I:0/30 I:0/30 B3:0/12 O:0/2

```

Each zone monitors for product accumulation and stops its motor when full while allowing upstream zones to continue until they also fill. When downstream capacity becomes available, zones release products in sequence to maintain smooth flow.

The accumulation system includes gentle pressure control to prevent product damage while maintaining positive product control for reliable release when downstream processes are ready.

Chapter 3: Process Control Examples

Temperature Control with PID

Process temperature control requires sophisticated algorithms that can maintain precise temperatures despite varying loads, ambient conditions, and disturbances. This example demonstrates PID control implementation for a heating process.

```

Rung 0000: Temperature Control Mode Selection

|----] [----------]/[----------( )-------------|

Auto_Mode Manual_Mode Temp_Auto_Enable

I:0/0 I:0/1 B3:0/0

Rung 0001: PID Control Block

|----] [-------------------------(PID)---------|

Temp_Auto_Enable PID

B3:0/0 Control Block: N7:0

Process Variable: N7:10

Setpoint: N7:11

Output: N7:12

Rung 0002: Analog Output Scaling

|----] [-------------------------(SCL)---------|

Temp_Auto_Enable SCALE

B3:0/0 Source: N7:12

Rate: 163

Offset: 6554

Dest: O:1/0

Rung 0003: Manual Mode Output

|----] [-------------------------(MOV)---------|

Manual_Mode MOVE

B3:0/1 Source: N7:15

Dest: O:1/0

```

The PID control block automatically adjusts the heating output to maintain the temperature setpoint despite changes in ambient conditions, product load, or process disturbances. Proper PID tuning is essential for stable, responsive temperature control.

The system includes both automatic and manual control modes with bumpless transfer between modes to prevent process upsets during mode changes. Alarm limits monitor for temperatures outside acceptable ranges.

Batch Processing Control

Batch manufacturing requires precise sequencing, timing, and ingredient management. This example demonstrates a simple batch mixing process with ingredient addition, mixing time control, and discharge sequencing.

```

Rung 0000: Batch Start Conditions

|----] [----------] [----------] [----------( )-----|

Batch_Start Tank_Empty Recipe_Ready Batch_Active

I:0/0 I:0/10 B3:0/10 B3:0/0

Rung 0001: Ingredient A Addition

|----] [----------]/[----------(TON)-------------|

Batch_Active IngA_Complete T4:0

B3:0/0 B3:0/1 Timer ON

Preset: 150

Accum: 0

|----] [----------]/[----------( )-------------|

T4:0/TT T4:0/DN IngA_Valve

T4:0/TT T4:0/DN O:0/0

|----] [----------------------------( )--------|

T4:0/DN IngA_Complete

B3:0/1

Rung 0002: Ingredient B Addition

|----] [----------] [----------(TON)----------|

IngA_Complete IngB_Complete T4:1

B3:0/1 B3:0/2 Timer ON

Preset: 200

Accum: 0

Rung 0003: Mixing Control

|----] [----------] [----------(TON)----------|

IngB_Complete Mix_Complete T4:2

B3:0/2 B3:0/3 Timer ON

Preset: 600

Accum: 0

|----] [----------]/[----------( )----------|

T4:2/TT Mix_Complete Mixer_Run

T4:2/TT B3:0/3 O:0/1

```

The batch sequence ensures that ingredients are added in the correct order with proper timing between additions. The mixing phase provides adequate blending time before discharge, and the system prevents starting a new batch until the tank is confirmed empty.

Recipe management enables different product formulations with varying ingredient quantities and processing times. The system includes material tracking and batch documentation for quality control and regulatory compliance.

Level Control System

Liquid level control systems maintain tank levels within specified ranges while managing inflow and outflow variations. This example demonstrates a level control system with pump control and overflow protection.

```

Rung 0000: Level Control Logic

|----] [----------]/[----------]/[---------( )---|

Level_Low Level_High Pump_Fault Fill_Pump

I:0/0 I:0/1 I:0/10 O:0/0

Rung 0001: High Level Alarm

|----] [-------------------------( )----------|

Level_High High_Level_Alarm

I:0/1 O:0/10

Rung 0002: Low Level Alarm

|----] [-------------------------( )----------|

Level_Low Low_Level_Alarm

I:0/0 O:0/11

Rung 0003: Emergency Drain Control

|----] [----------] [-----------( )----------|

Level_Emergency Tank_Drain_Enable Emerg_Drain

I:0/2 B3:0/0 O:0/1

```

The level control system uses simple on/off control with level switches to maintain the tank level between minimum and maximum limits. The fill pump starts when the level drops below the low switch and stops when the level reaches the high switch.

Safety features include high-level alarms, emergency drain capability, and pump fault monitoring. These protective measures prevent tank overflow and ensure safe operation under abnormal conditions.

Chapter 4: Safety System Examples

Emergency Stop System

Safety systems must be designed to fail safely and provide reliable protection under all conditions. This example demonstrates proper emergency stop implementation with safety relay monitoring and diagnostic capabilities.

```

Rung 0000: Safety Input Monitoring

|----] [----------] [----------] [----------( )---|

E_Stop_1 E_Stop_2 Safety_OK Safety_System

I:0/0 I:0/1 I:0/10 B3:0/0

Rung 0001: Safety System Diagnostics

|----]/[----------] [----------]/[---------( )---|

Safety_System E_Stop_1 E_Stop_2 Safety_Fault

B3:0/0 I:0/0 I:0/1 B3:0/1

Rung 0002: Motor Control with Safety

|----] [----------] [----------] [----------( )---|

Motor_Start Safety_System Motor_Enable Motor_Run

I:0/2 B3:0/0 B3:0/10 O:0/0

|----] [---------------------------------------------|

Motor_Run

O:0/0

Rung 0003: Safety Reset Logic

|----] [----------] [----------]/[---------( )---|

Safety_Reset Safety_System Safety_Fault Reset_Enable

I:0/3 B3:0/0 B3:0/1 B3:0/10

|----] [----------]/[----------(OSR)--------( )---|

Reset_Enable Reset_Trigger B3:1/0 Safety_Reset_Pulse

B3:0/10 B3:0/11

```

The safety system monitors multiple emergency stop devices and prevents any controlled equipment from operating when emergency stops are activated. Diagnostic logic detects failures in the safety input circuits and prevents reset until faults are corrected.

Safety system reset requires deliberate operator action and cannot occur automatically. The system includes comprehensive diagnostics and testing capabilities to verify continued safe operation.

Light Curtain Integration

Light curtains provide perimeter protection for automated equipment while allowing normal operation when the protected area is clear. This example demonstrates proper light curtain integration with muting and reset requirements.

```

Rung 0000: Light Curtain Status

|----] [----------] [----------( )-------------|

Light_Curtain Mute_Active LC_Clear

I:0/0 B3:0/1 B3:0/0

Rung 0001: Muting Control Logic

|----] [----------] [----------] [------(TON)---|

Mute_Request Cycle_Active Part_Present T4:0

I:0/1 B3:0/10 I:0/11 Timer ON

Preset: 50

Accum: 0

|----] [----------] [----------( )-------------|

T4:0/TT Cycle_Complete Mute_Active

T4:0/TT B3:0/11 B3:0/1

Rung 0002: Machine Cycle Control

|----] [----------] [----------] [------( )----|

Cycle_Start LC_Clear Safety_OK Machine_Enable

I:0/2 B3:0/0 B3:0/20 B3:0/10

Rung 0003: Cycle Reset Requirements

|----] [----------]/[----------( )-------------|

Reset_Button Machine_Enable Cycle_Reset

I:0/3 B3:0/10 B3:0/21

```

The light curtain system includes muting capability that temporarily disables the light curtain during normal part transfer while maintaining protection at all other times. Muting is automatically canceled when the cycle completes or if abnormal conditions are detected.

Reset requirements ensure that operators must take deliberate action to restart the system after a safety stop, and the system includes comprehensive monitoring of safety device status and diagnostic capabilities.

Lockout/Tagout Integration

Lockout/Tagout (LOTO) procedures require positive isolation of energy sources during maintenance. This example demonstrates PLC integration with LOTO systems including energy isolation verification and maintenance mode control.

```

Rung 0000: Energy Isolation Status

|----] [----------] [----------] [----------( )---|

Electrical_ISO Pneumatic_ISO Hydraulic_ISO Energy_Isolated

I:0/0 I:0/1 I:0/2 B3:0/0

Rung 0001: Maintenance Mode Enable

|----] [----------] [----------] [----------( )---|

Maint_Key Energy_Isolated LOTO_Complete Maint_Mode

I:0/10 B3:0/0 B3:0/1 B3:0/10

Rung 0002: Production Interlock

|----]/[------------------------( )-------------|

Maint_Mode Prod_Enable

B3:0/10 B3:0/11

Rung 0003: Maintenance Diagnostics

|----] [----------] [----------]/[---------( )---|

Maint_Mode Diagnostic_OK Maint_Fault Maint_Status

B3:0/10 B3:0/20 B3:0/21 O:0/10

```

The LOTO integration prevents production equipment from operating when maintenance mode is active and verifies that all energy sources are properly isolated before allowing maintenance activities. The system includes positive feedback from isolation devices and LOTO verification.

Maintenance mode provides controlled access to equipment functions needed for troubleshooting and repair while maintaining appropriate safety interlocks and preventing inadvertent startup.

Chapter 5: Advanced Control Examples

Recipe Management System

Modern manufacturing often requires flexible production capabilities with multiple product recipes. This example demonstrates a basic recipe management system with parameter loading and batch tracking.

```

Rung 0000: Recipe Selection Logic

|----] [----------(EQU)----------] [------( )----|

Recipe_Load EQUAL Recipe_1 Recipe_1_Active

B3:0/0 Source A: N7:0 N7:0 B3:0/1

Source B: 1 1

|----] [----------(EQU)----------] [------( )----|

Recipe_Load EQUAL Recipe_2 Recipe_2_Active

B3:0/0 Source A: N7:0 N7:0 B3:0/2

Source B: 2 2

Rung 0001: Recipe Parameter Loading

|----] [----------(COP)---------------------------|

Recipe_1_Active COPY

B3:0/1 Source: #N10:0

Dest: #N7:10

Length: 10

|----] [----------(COP)---------------------------|

Recipe_2_Active COPY

B3:0/2 Source: #N10:20

Dest: #N7:10

Length: 10

Rung 0002: Batch Documentation

|----] [----------(ADD)---------------------------|

Batch_Complete ADD

B3:0/10 Source A: N7:50

Source B: 1

Dest: N7:50

|----] [----------(MOV)---------------------------|

Batch_Complete MOVE

B3:0/10 Source: N7:0

Dest: N7:51

```

The recipe system stores multiple parameter sets and loads the appropriate parameters based on operator selection or production scheduling. Parameter sets include temperatures, times, quantities, and other process variables specific to each product.

Batch tracking records production information including recipe used, batch quantities, processing times, and quality data for traceability and process improvement analysis.

Statistical Process Control

Quality control requires monitoring process parameters and detecting trends that indicate developing problems. This example demonstrates basic statistical process control with alarm generation for out-of-specification conditions.

```

Rung 0000: Sample Collection

|----] [----------(MOV)---------------------------|

Sample_Trigger MOVE

B3:0/0 Source: N7:0

Dest: N7:10

|----] [----------(ADD)---------------------------|

Sample_Trigger ADD

B3:0/0 Source A: N7:11

Source B: 1

Dest: N7:11

Rung 0001: Running Average Calculation

|----] [----------(DIV)---------------------------|

B3:0/0 DIVIDE

Source A: N7:12

Source B: N7:11

Dest: N7:13

Rung 0002: Control Limit Checking

|----] [----------(GRT)----------] [------( )----|

B3:0/0 GREATER THAN N7:14 High_Alarm

Source A: N7:13 N7:14 B3:0/1

Source B: N7:14

|----] [----------(LES)----------] [------( )----|

B3:0/0 LESS THAN N7:15 Low_Alarm

Source A: N7:13 N7:15 B3:0/2

Source B: N7:15

```

The SPC system collects measurement samples, calculates running averages and control limits, and generates alarms when processes drift outside acceptable ranges. This early warning enables corrective action before defective products are produced.

Trend analysis and data logging provide information for process improvement and predictive maintenance programs while maintaining historical records for quality audits and regulatory compliance.

Conclusion: Applying Programming Examples to Real Projects

These programming examples demonstrate the fundamental techniques and patterns used in professional industrial automation applications. Each example builds on previous concepts while introducing new programming techniques and problem-solving approaches that you can apply to your own projects.

The key to mastering PLC programming lies in understanding these fundamental patterns and adapting them to specific application requirements. Practice with these examples, modify them for different scenarios, and combine techniques from multiple examples to create solutions for complex industrial control problems.

Remember that good programming involves more than just making systems work – it requires creating maintainable, documented, and reliable code that other technicians can understand and modify. The examples in this guide demonstrate professional programming practices that will serve you well throughout your automation career.

Continue developing your skills by implementing these examples on actual PLC hardware or simulation software, experimenting with variations and improvements, and studying how experienced programmers solve complex control challenges in your specific industry or application area.