29 panel-wiring fundamentals and 19 fault-diagnosis scenarios. Each lesson runs in your browser with a virtual multimeter, drag-route wiring, and per-connection grading.
29 lessons covering panel layout, sensors, motors, safety, and communications.
In this lesson you will wire a 24 VDC DIN-rail power supply to the PLC base unit and establish a solid earth ground through the ground bar. Connect the AC ma…
See lesson →Industrial 3-wire proximity sensors use a standard colour code across almost every manufacturer:
See lesson →A **retro-reflective photoelectric sensor** (photoeye) emits an infrared beam toward a fixed reflector. While the return beam reaches the receiver the output…
See lesson →A PLC digital output is a small-signal transistor or relay. Its current rating is typically 0.1–0.5 A — enough to drive a pilot lamp or a small sensor, b…
See lesson →Not all sensors push a defined voltage onto their signal wire. An **NPN (open-collector) sensor** contains an NPN transistor whose collector is exposed direc…
See lesson →Industrial process instruments — pressure transmitters, temperature sensors, flow meters — communicate their measurements using a **4-20 mA current loop*…
See lesson →A **Variable Frequency Drive** (VFD) controls the speed of a 3-phase induction motor by varying the frequency and voltage of the AC power it delivers to the …
See lesson →EN ISO 13849-1 defines Performance Levels (PL a–e) for safety functions. Category 3 mandates **single-fault tolerance**: a single failure anywhere in the s…
See lesson →Modbus RTU communicates over RS-485 — a differential signalling standard designed for long cable runs in electrically noisy industrial environments. Instea…
See lesson →Traditional fieldbuses — RS-485 Modbus, PROFIBUS, DeviceNet — were designed when 9600 bps was fast and network management tools barely existed. Industria…
See lesson →An incremental quadrature encoder produces two digital pulse trains — A and B — that are 90° out of phase with each other. Because of this phase offset,…
See lesson →The **three-wire motor starter** is the most common motor control circuit in industrial automation. You will find it on conveyors, pumps, fans, and compresso…
See lesson →An **emergency stop (E-stop)** button is the physical switch a machine operator uses to immediately halt a dangerous machine. Pressing the mushroom-head butt…
See lesson →A **Variable Frequency Drive (VFD)** controls motor speed by converting fixed-frequency AC mains to variable-frequency AC output. The core insight you must t…
See lesson →**RS-485** is the physical-layer standard used by Modbus RTU — the most widely deployed fieldbus protocol in industrial automation. You will encounter it o…
See lesson →**Prerequisite:** complete Wiring 13 (E-Stop Chain) first. That lab teaches the single-channel NC E-stop loop. This lab extends it to the **Cat 3 / PLd** saf…
See lesson →Build the front end of a real control panel: incoming three-phase supply, door interlocked main isolator, branch circuit breaker, 24 VDC power supply, fused …
See lesson →Connect three common volt-free field devices to PLC inputs: a maintained selector switch, a mechanical limit switch and a tank float switch. The devices do n…
See lesson →Drive a 24 VDC pneumatic solenoid through an interposing relay. The PLC output only energises the relay coil; the relay contact switches the field load. Add …
See lesson →Build both halves of a direct-on-line starter: the three-phase power path through isolator, breaker, contactor and thermal overload to the motor, plus the 24…
See lesson →Wire paired forward and reverse contactors. The forward contactor preserves phase order; the reverse contactor swaps L1 and L3 before the common overload. A …
See lesson →Terminate a three-wire Pt100 resistance temperature detector on a dedicated PLC temperature input. The single A conductor lands on RTD-A; the two same-colour…
See lesson →Connect a low-level thermocouple signal directly to a temperature input card with correct polarity and a single-point shield. Thermocouple extension wire mus…
See lesson →Connect a Type 4 light curtain to a safety relay using two independent OSSD channels, then use a safety output contact to interrupt a contactor coil. Functio…
See lesson →Integrate a dual-channel guard switch, safety relay and VFD Safe Torque Off inputs. Add the ordinary run command and hardwired running/fault feedback to a PL…
See lesson →Connect a three-wire IO-Link sensor to Port 1 of an IO-Link master and link the master to the PLC network. L+ and L− power the field device; C/Q carries bi…
See lesson →Wire a 4–20 mA analog output to a smart valve positioner, return its position feedback to an analog input, and connect a HART communicator in parallel acro…
See lesson →Terminate a six-wire strain-gauge load cell on a weighing transmitter, including excitation, millivolt signal, sense conductors and shield. Send the transmit…
See lesson →Build an intrinsically safe analog loop across the safe-area / hazardous-area boundary. The galvanic barrier limits the electrical energy that can reach the …
See lesson →19 planted-fault scenarios. Use the multimeter to trace and diagnose.
Welcome to fault-finding. From here on every lesson hands you a pre-wired panel with a problem buried in it; your job is to find the fault using the multimet…
See lesson →**Symptom:** the line operator reports the conveyor's safety-OK indicator never came on this morning. You walk to the panel — the PSU LED is on, the relay …
See lesson →**Symptom:** the line operator reports the conveyor contactor never pulled in this morning — the panel went dark on the load side. You walk over: the PSU's…
See lesson →**Symptom:** the morning shift calls — the panel won't power up. You walk over: the PSU indicator LED is on, but the PLC base is completely dark. None of t…
See lesson →**Symptom:** the PLC is commanding contactor KM1 to pull in — the output is on, you can hear the program asking for it — but the contactor isn't engaging…
See lesson →**Symptom:** the line operator reports the conveyor isn't indexing — the PLC isn't reacting to the photoeye on the infeed. You walk over to the panel.
See lesson →**Symptom:** the line operator reports the conveyor's box-present signal at PLC input X0 has been stuck **HIGH** all morning even when the conveyor is empty.…
See lesson →**Symptom:** the night-shift operator phoned: the panel's alarm beacon and X0 input have been ON since power-up, and there's no actual alarm condition — th…
See lesson →**Reported symptom:** The incoming supply and PSU indicators are healthy, but the +24 V distribution rail is dead.
See lesson →**Reported symptom:** K1 pulls in, but YV1 chatters and measures low voltage only while energised.
See lesson →**Reported symptom:** The control supply is healthy and Start works mechanically, but KM1 cannot energise.
See lesson →**Reported symptom:** The light curtain is interrupted, yet the contactor coil path remains continuous.
See lesson →**Reported symptom:** The Pt100 channel is over-range and the input card reports a sensor-break diagnostic.
See lesson →**Reported symptom:** The indicated temperature falls when the process heats up and rises as it cools.
See lesson →**Reported symptom:** The valve local display is at 50%, but PLC feedback is consistently 7.5% high across the range.
See lesson →**Reported symptom:** Modbus works at low baud rate but becomes intermittent at the normal rate, especially on long cable runs.
See lesson →**Reported symptom:** The guard is closed and the safety relay resets, but the VFD remains in STO active / inhibit.
See lesson →**Reported symptom:** The IO-Link sensor stays powered but repeatedly drops to COMLOST when the machine vibrates.
See lesson →**Reported symptom:** The weighing value moves negative when test weight is applied, while excitation and zero stability are normal.
See lesson →5 foundation wiring labs are Free; advanced and fault-diagnosis labs are Pro.
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