Industrial Automation Glossary

A Programmable Logic Controller (PLC) is an industrial digital computer hardened for factory-floor environments. It executes a user-written program on a deterministic scan cycle to read sensor inputs, run logic, and drive actuator outputs.

Major families repaired by Flexa Systems: Allen-Bradley ControlLogix, CompactLogix, SLC 500, PLC-5, MicroLogix; Siemens S7-1500, S7-1200, S7-300/400, legacy S5; Mitsubishi MELSEC iQ-R, iQ-F, Q Series, FX Series; Omron Sysmac NJ/NX, CJ2, CS1, CP1, C200H; GE Fanuc RX3i, RX7i, Series 90-30, 90-70, VersaMax; Schneider Modicon M340, Quantum, Premium.

Typical failure modes: CPU boot failure, battery-backed memory loss, I/O module output driver failure, communication module transceiver degradation, power supply capacitor wear.

The PLC scan cycle is the deterministic sequence a programmable logic controller executes continuously: read inputs → execute user logic → update outputs → housekeeping. Typical scan times range from 1 ms to 100 ms depending on CPU class and program size.

Abnormal scan-time growth is a diagnostic signal — it often indicates a failing CPU, memory fragmentation, or a stuck communication task. Flexa Systems verifies scan-time stability on every repaired PLC before return.

Ladder logic (LD) is a graphical programming language for PLCs that resembles electrical relay schematics, with power rails on either side and logic rungs in between. It is one of five languages defined in IEC 61131-3 — the international standard for industrial control programming.

Other IEC 61131-3 languages: Function Block Diagram (FBD), Structured Text (ST), Sequential Function Chart (SFC), and Instruction List (IL). Flexa Systems backs up ladder logic, structured text, and function block programs before every CPU repair — no engineering data loss.

A Human-Machine Interface (HMI) is the graphical operator console that displays process state and accepts operator input on an industrial machine or production line. Modern HMIs are touchscreen-based and communicate with PLCs over Ethernet/IP, Modbus, or Profinet.

Major HMI families repaired: Allen-Bradley PanelView Plus 6 and 7; Siemens SIMATIC KTP, Comfort Panel, TP Series; Pro-face GP / LT / ST; Weintek MT8000 / cMT series; Mitsubishi GOT1000 / GOT2000; Omron NB / NS.

Typical failure modes: LCD backlight dim or failed, touchscreen digitizer dead zones, power supply dropout, communication port failure, internal battery loss of retentive data.

SCADA (Supervisory Control And Data Acquisition) is the software layer above PLCs and HMIs that aggregates data from multiple controllers across a plant, presents it on a control-room display, stores historical trends, and issues supervisory commands. Common platforms: Rockwell FactoryTalk View, Siemens WinCC, Wonderware / AVEVA System Platform, Ignition by Inductive Automation.

A Distributed Control System (DCS) is a process-control architecture where controllers are distributed throughout the plant (rather than centralized), each responsible for a process area, and tied together by a plant-wide network. DCS is the standard in continuous process industries — chemical, oil & gas, power generation. Common platforms: Honeywell Experion, Emerson DeltaV, Yokogawa CENTUM, ABB System 800xA.

A Variable Frequency Drive (VFD) — also called AC drive, adjustable speed drive (ASD), or inverter — controls the speed and torque of an AC induction or permanent-magnet motor by varying the frequency and voltage of the power supplied to it. A VFD typically converts fixed-frequency AC to DC (rectifier), then uses PWM switching of IGBTs to synthesize variable-frequency AC output.

Major VFD families repaired: Allen-Bradley PowerFlex 4, 40, 70, 400, 525, 700, 753, 755; Siemens SINAMICS G110, G120, G130, S120, V20, Micromaster 4; ABB ACS55, ACS355, ACS550, ACS800, ACS880, ACH580; Yaskawa A1000, V1000, E7, F7, GA700, P1000; Danfoss VLT 2800/5000/6000, FC 102, FC 302; Lenze 8200/8400, i550; Mitsubishi FR-A700/A800, FR-E700; Schneider Altivar; Fuji Electric FRENIC.

Typical failure modes: IGBT module short, DC-bus capacitor bank capacitance loss (electrolytic dry-out), gate driver IC failure, fan failure causing thermal shutdown, input rectifier diode failure, control board firmware corruption.

A servo drive (or servo amplifier) is a closed-loop motor controller that precisely regulates position, velocity, and torque of a servo motor using high-resolution feedback (encoder or resolver) and a fast-update control loop (typically 1–16 kHz). Servo drives are used where an AC induction drive is too imprecise — machine tools, CNC, robotics, packaging, printing, semiconductor fab.

Major servo families repaired: Allen-Bradley Kinetix 300, 350, 2000, 5500, 5700, 6000, 6500; Yaskawa Sigma-II, Sigma-5, Sigma-7; Fanuc Alpha-i (αi) and Beta-i (βi) series; Mitsubishi MR-J2, MR-J3, MR-J4, MR-J5; Siemens SINAMICS S120 servo modules, Simodrive 611; Omron Sigma-5 OEM, G5, 1S; Parker Compax3, Aries, Dynaserv.

An IGBT (Insulated-Gate Bipolar Transistor) is a high-power switching semiconductor that combines the easy gate-drive characteristic of a MOSFET with the high current-handling and low saturation voltage of a bipolar transistor. IGBTs are the core switching element in VFDs and servo drives — typically arranged in a three-phase bridge that synthesizes variable-frequency AC from a DC bus via pulse-width modulation (PWM).

IGBT failure is the single most common high-cost fault in a VFD. Symptoms include smoke/explosion, drive "OF" (overcurrent) fault at start, and measurable collector-to-emitter short. Flexa Systems replaces individual IGBT modules rather than swapping the full power stack — typical repair saves 40–70% vs. a new drive.

The DC bus (or DC-link) is the rectified, capacitor-smoothed DC voltage inside a VFD or servo drive that feeds the inverter stage. Typical voltages: 325 V DC for a 230 V-in drive, 650 V DC for a 480 V-in drive. Capacitor bank condition directly affects drive stability, PWM quality, and ride-through performance.

Electrolytic DC-bus capacitors degrade over 8–12 years due to dielectric dry-out. Symptoms of a failing bus capacitor: audible 120 Hz hum, erratic shutdowns, "DC Bus Ripple" faults. Capacitor bank replacement extends drive life by another full service interval at a fraction of replacement cost.

Pulse-Width Modulation (PWM) is the technique VFDs and servo drives use to synthesize an AC sine wave from a DC bus. Fast switching (typically 2–16 kHz) of IGBTs produces pulses whose width varies — their running average approximates the target sine wave. Higher PWM frequencies give smoother motor current and quieter operation at the cost of higher IGBT switching losses.

EtherNet/IP is an industrial Ethernet protocol developed by Rockwell Automation and managed by ODVA. It carries the Common Industrial Protocol (CIP) over standard Ethernet, enabling real-time I/O and messaging across a plant network. EtherNet/IP is the dominant protocol in Allen-Bradley installations throughout North American manufacturing.

PROFINET is the Siemens-originated industrial Ethernet protocol standardized by PI (Profibus & Profinet International). It supports real-time (RT) and isochronous real-time (IRT) communication for motion control, alongside standard TCP/IP services for diagnostics and configuration. PROFINET is the dominant protocol in Siemens-based European installations.

EtherCAT is a high-performance industrial Ethernet protocol developed by Beckhoff and standardized by the EtherCAT Technology Group (ETG). It uses a "processing on-the-fly" technique where a single Ethernet frame passes through all slaves in a daisy chain, reading and writing data in transit — achieving sub-microsecond jitter and cycle times below 100 µs. Widely adopted in motion control, robotics, and packaging.

Modbus is a simple master-slave serial (RTU/ASCII) or client-server Ethernet (TCP) protocol originally developed by Modicon (now Schneider Electric) in 1979. It remains one of the most widely deployed industrial protocols due to its simplicity and royalty-free specification — common in HVAC, water/wastewater, and power monitoring.

An encoder is a position-feedback device fitted to a motor shaft that reports shaft angle to a servo drive or motion controller. Incremental encoders emit quadrature A/B pulses (count-per-revolution, CPR); absolute encoders report an exact multi-turn position over a digital serial bus (SSI, BiSS-C, EnDat, Hiperface). Resolvers provide the same function with an analog two-phase excitation — rugged enough for high-temperature and high-vibration environments.

Aluminum electrolytic capacitors are the workhorses of the DC bus in VFDs, servo drives, and industrial power supplies. Their capacitance and equivalent series resistance (ESR) degrade over 8–12 years of operation due to electrolyte dry-out — the single most common wear failure in industrial drives. Capacitor bank replacement is a standard service step in drive refurbishment.

An optocoupler (optoisolator) transmits a signal from one electrical circuit to another using a short optical light path — providing galvanic isolation between low-voltage control logic and high-voltage power circuits, or between different ground domains. PLC digital I/O output modules use optocouplers to isolate field-side loads from the CPU backplane.

Component-level repair (also called board-level or IC-level repair) means diagnosing and replacing individual components on a failed circuit board — IGBTs, capacitors, gate driver ICs, MOSFETs, resistors — rather than swapping the entire board or module. It is significantly more cost-effective than module replacement (30–60% of replacement cost typical) and is the only option when modules are discontinued by the OEM.

Mean Time Between Failures (MTBF) is the predicted average operating time between one failure and the next for a repairable system. For industrial drives, MTBF is typically 60,000–100,000 hours (7–12 years continuous operation). MTBF should not be confused with service life or warranty period.

A functional test (load test) applies realistic operating conditions to a repaired unit — rated voltage, rated current, through a representative motor load — to verify the repair holds under actual operating stress. Flexa Systems performs full-load functional testing on every VFD and servo drive repair before return, including under-load thermal soak on high-kW units.

A refurbished (reconditioned) unit is a used industrial drive, PLC, or HMI that has been fully inspected, rebuilt at component level (replacing all wear items such as capacitors, fans, batteries), functionally tested under load, and covered by a new warranty. A refurbished unit from Flexa Systems carries the same 2-year warranty as a fresh repair — unlike OEM-surplus or dealer stock, which is sold as-is.