TryPLC Blog — PLC programming, robotics and industrial protocols
In-depth technical guides on IEC 61131-3 Structured Text, PLC hardware, industrial communication protocols, motion control and automation careers — written by practising automation engineers. 56 articles.
Analog Input Reads 0 or Overrange: Troubleshooting a 4–20 mA Loop
Your transmitter display says 3.2 bar but the PLC shows 0 or a wire-break alarm. Here is the measuring order that finds the cause in minutes.
Sensor LED Is On but the PLC Input Is Off: PNP vs NPN Wiring
The sensor LED lights, the PLC input does not. Nine times out of ten the sensor and the input card disagree about which way current flows.
VFD Trips on Overcurrent at Start: Causes, Checks and Fixes
The drive trips the moment you press start. Here is how to tell a parameter problem from a mechanical one, and a mechanical one from a damaged cable.
Modbus TCP Timeout or No Response: A Diagnosis Order That Works
Your Modbus client times out, or connects but reads nonsense. Work from the cable up to the register map and the fault reveals itself.
PROFINET Device Shows BF Red: Fixing "No Connection" Step by Step
The ET 200SP is powered, the cable is plugged in, and BF is red. Almost always it is the device name — here is how to prove it and fix it.
Encoder Position Jumps or Drifts: High-Speed Counter Troubleshooting
The axis returns to the same spot but the count is 40 pulses different each time. Electrical noise, a wrong counter mode or mechanical slip — here is how to tell.
PLC Output Is On but the Cylinder Does Not Move: Solenoid Valve Checks
The output LED is lit and the program says extend, but the cylinder sits still. Split the chain into electrical, pneumatic and mechanical and you will find it fast.
PLC Loses Counters and Setpoints After Power Off: Retentive Memory Explained
Every Monday the shift totals and recipe setpoints are back to zero. Here is how retentive memory really works, and how to make values survive.
Safety Relay Will Not Reset After an Emergency Stop: Diagnosis Guide
The E-stop is pulled out, the reset button is pressed, and the safety relay stays off. Follow the relay’s own logic and its LEDs tell you which condition is missing.
Modbus RTU on RS-485: CRC Errors and Intermittent Communication
Most polls work, a few fail with CRC errors, and it gets worse when the pumps run. RS-485 is electrical first — fix the bus and the protocol behaves.
PT100 Temperature Reading Is Wrong: RTD Troubleshooting for PLCs
The tank is at 60 °C and the PLC says 64.8 °C. With a PT100, a few ohms of cable are a few degrees of error — here is how to find them.
HMI Shows #### or "Communication Lost": Finding the Broken Link
Every value on the screen turned into ####. Is it the network, the PLC, or the HMI project? A short sequence separates the three.
PLC CPU Goes to STOP With a Red Error LED: Reading the Diagnostics
The machine stops, the CPU shows STOP and ERROR. Before downloading anything, read what the controller already told you.
Random PLC Resets and Faults: Finding 24 V Supply Dips
Faults appear with no pattern in the program, but always near a big load switching. The 24 V supply is the suspect — here is how to catch it.
Servo Following Error Fault: Causes, Checks and Tuning
The axis faults with "following error exceeded" at the end of every fast move. The drive is telling you the motor cannot keep up — find out why.
Noisy or Offset Analog Signal: Ground Loops and How to Break Them
The flow reading wanders by 3% and jumps when the pump starts. If the loop is fine on the bench, it is probably a ground loop — here is how to prove it.
HMI Programming Guide: Screens, Alarms, and Tag Mapping That Operators Actually Trust
A practical, vendor-neutral HMI programming guide covering screen hierarchy, ISA-101 layout, alarm management, and tag mapping between the PLC and the operator panel.
Best Online Training for PLC, Robotics, Industrial Communication, and Motion Control in 2026
A 2026 ranked guide to the best online platforms for learning PLC programming, industrial robotics, communication protocols, and motion control — written by practicing automation engineers.
PLC Safety Programming: SIL-Rated Logic & Safety Function Blocks in Structured Text
Design SIL-rated safety logic in Structured Text — covering dual-channel monitoring, safe shutdown sequences, diagnostic coverage, and IEC 62061 / IEC 61508 compliance patterns.
PLC Network Communication: Modbus TCP & EtherNet/IP in Structured Text
Connect PLCs to sensors, drives, and SCADA systems over industrial Ethernet — with production-grade Modbus TCP and EtherNet/IP implementations in Structured Text.
PLC Program Organization Units: Structuring Code That Scales — IEC 61131-3 Best Practices
Stop writing monolithic PLC programs. Learn the IEC 61131-3 POU architecture — when to use PROGRAM vs FUNCTION vs FUNCTION_BLOCK, and how to structure projects that scale from 10 I/O to 10,000.
PLC Error Handling & Exception Management: Building Fault-Tolerant Structured Text
PLCs don't have try/catch — so how do you handle errors? Build fault-tolerant automation with defensive coding patterns, hierarchical fault propagation, and graceful degradation strategies.
PLC Data Logging & Historian Integration: CSV, Ring Buffers & Time-Series in Structured Text
Build production-grade data logging directly in your PLC — ring buffers, timestamped CSV records, event-triggered snapshots, and historian integration patterns in Structured Text.
PLC Object-Oriented Programming: Methods, Interfaces & Inheritance in Structured Text
Modern PLCs support OOP — and it changes everything. Learn how methods, interfaces, inheritance, and polymorphism let you build automation libraries that scale across machines and projects.
PLC Power-Up Initialization & Startup Sequences: Safe Boot Logic in Structured Text
What happens in the first 5 seconds after power-up determines whether your machine starts safely or damages itself. Build bulletproof PLC initialization sequences with proven Structured Text patterns.
PLC Cybersecurity & IEC 62443: Protecting Industrial Networks in the Connected Age
Your PLC is now on the network — and attackers know it. Learn IEC 62443 defense-in-depth, zone segmentation, access control patterns, and how to write Structured Text that resists tampering.
PLC Troubleshooting & Debugging: Systematic Techniques for Structured Text
Stop randomly changing code and hoping it works. Learn the systematic debugging techniques that experienced PLC programmers use — from watch tables and force tables to state machine tracing and online monitoring.
PLC Energy Management: Power Monitoring, Load Shedding & Demand Control in Structured Text
Electricity is your factory's second-largest cost. Build PLC-based energy management with power monitoring, intelligent load shedding, demand prediction, and ISO 50001 KPI tracking in Structured Text.
PLC Packaging Machine Programming: Cam Sequencing, Reject Systems & OEE in Structured Text
High-speed packaging demands precise timing, reliable product tracking, and zero-tolerance reject systems. Build production-grade packaging machine logic with cam sequencing, tracking arrays, and real-time OEE in Structured Text.
Understanding EDS & XML Device Files: Configuring PLCs and Field Devices
Every time you add a drive, sensor, or I/O module to your PLC network, you need a device file. Learn what EDS, GSD, GSDML, and IODD files are, how to read them, and how they configure your fieldbus devices.
PLC Serial Communication: RS232, RS485, Modbus RTU/TCP & Communication Layers Explained
Understand PLC serial communication from the physical wire up — RS232 vs RS485, TX/RX data flow, Modbus RTU vs TCP framing, and the 7-layer OSI model mapped to industrial protocols.
PLC PROFINET IO Configuration: GSDML Files, IO Devices & Structured Text Data Exchange
Configure PROFINET IO devices from scratch — understand GSDML files, slot/subslot mapping, IO data exchange, and diagnostic handling in Structured Text.
ISA-88 Batch Control & Recipe Management in Structured Text: Complete Implementation Guide
Build a complete ISA-88 batch control system — from recipe parameter tables and procedural state machines to unit allocation and phase logic in Structured Text.
PLC Water Treatment & SCADA Integration: Complete Structured Text Programming Guide
Build a water treatment control system from intake to distribution — with pump sequencing, chemical dosing PID loops, filter backwash logic, and SCADA integration in Structured Text.
PLC Conveyor Sorting System: Complete Structured Text Tutorial with Sensor Logic & Diverter Control
Program a multi-lane conveyor sorting system from scratch — with photoelectric sensor logic, product tracking arrays, pneumatic diverter timing, and reject bin management in Structured Text.
PLC HVAC & Building Automation: Complete Structured Text Programming Guide
Build a complete HVAC building automation system — with AHU damper control, VAV zone logic, chiller plant sequencing, occupancy-based scheduling, and energy optimization in Structured Text.
PLC CIP (Clean-in-Place) Systems for Food & Beverage: Structured Text Programming Guide
Implement a complete CIP clean-in-place system — with multi-step wash sequences, chemical concentration control, temperature/flow validation, and regulatory compliance logging in Structured Text.
PLC Motion Control & Servo Programming: PLCopen Function Blocks in Structured Text
From enabling a servo axis to synchronized multi-axis camming — the complete guide to PLCopen motion control function blocks implemented in IEC 61131-3 Structured Text.
PLC HMI Screen Design Best Practices: Building Operator Interfaces That Actually Work
Design HMI screens that reduce operator errors and speed up response times — with ISA-101 principles, color psychology, and the Structured Text data structures behind every great display.
PLC Analog Signal Scaling: Converting Raw Values to Engineering Units
Convert raw analog signals (0–27648, 4–20mA, 0–10V) to real-world engineering units with reusable Structured Text scaling functions.
PLC-to-SCADA Communication: OPC UA, Modbus & Industrial Protocols in Structured Text
Master PLC-to-SCADA communication with practical Structured Text patterns for OPC UA, Modbus TCP/RTU, PROFINET, and EtherNet/IP — including handshake logic and buffer management.
PLC Recipe Management & Batch Control: Implementing ISA-88 in Structured Text
Build production-grade recipe and batch control systems following the ISA-88 standard — with full Structured Text implementations for phase logic, recipe storage, and equipment modules.
PLC String Handling in Structured Text: Parsing, Formatting & Communication
Learn to manipulate strings in Structured Text — from basic concatenation to barcode parsing, HMI message formatting, and serial protocol handling.
PLC PID Control Loop Tuning: Implementation & Examples in Structured Text
Implement and tune PID controllers in Structured Text — from basic proportional control to full PID with anti-windup, used in temperature, pressure, and flow regulation.
10 PLC Programming Best Practices for Industrial Automation
Write better PLC code with these 10 industry-proven best practices for Structured Text programming in industrial automation.
PLC State Machine Design Patterns in Structured Text
Design robust, maintainable PLC programs using state machine patterns in Structured Text — the professional approach to sequential control.
PLC Alarm Management in Structured Text: Design Patterns & Best Practices
Build professional alarm management systems in Structured Text with priority handling, acknowledgment logic, first-out detection, and ISA-18.2 aligned design patterns.
PLC Motor Control with VFDs: Speed, Torque & Diagnostics in Structured Text
Master VFD control from your PLC — speed references, accel/decel ramps, torque limits, fault recovery, and real production sequencing patterns in Structured Text.
PLC Array Programming in Structured Text: FOR Loops, Sorting & Recipes
Master array handling in Structured Text — from basic FOR loops to recipe management and circular buffers used in real industrial applications.
PLC Counter Programming: CTU, CTD & CTUD Examples in Structured Text
Learn how to use CTU, CTD, and CTUD counters in Structured Text with practical industrial examples — from part counting to batch control.
PLC Data Types Explained: INT, REAL, BOOL & Type Conversion in Structured Text
Understand every IEC 61131-3 data type, when to use each one, and how to safely convert between them in Structured Text programs.
CODESYS vs TIA Portal: Structured Text Differences Every Engineer Should Know
Moving between CODESYS and TIA Portal? Learn the key Structured Text syntax differences to avoid common pitfalls.
How to Create Function Blocks in Structured Text: A Practical Tutorial
Function Blocks are the key to reusable, modular PLC code. Learn to create and use them effectively in Structured Text.
Ladder Logic vs. Structured Text: When to Use Each PLC Language
Should you use Ladder Logic or Structured Text? This comparison helps you choose the right IEC 61131-3 language for your project.
PLC Timer Programming: TON, TOF, and TP Timer Examples in Structured Text
Timers are essential in every PLC program. Learn how TON, TOF, and TP timers work with practical Structured Text examples.
Structured Text for Beginners: A Complete Guide to PLC Programming
Start your PLC programming journey with this beginner-friendly guide to Structured Text — the most versatile IEC 61131-3 language.