24 VDC control power
Why industrial panels run control circuits at 24 V DC, how the power supply works, and what the +24 V and 0 V rails are.
Relay vs contactor
What relays and contactors actually do, how they differ, and why a motor starter combines a contactor with an overload relay.
Control circuit vs power circuit
Every machine has two separate circuits. Understanding where the PLC sits — and the one link between the two worlds — is the key to reading any panel.
Reading electrical line diagrams
Rails, rungs, device symbols, and wire numbers — the complete picture for reading any industrial control schematic.
Fuses, breakers, and overload relays
Why the motor stopped and what protection device tripped it — fuses blow once, breakers reset, overload relays need a root cause before you reset them.
What is a PLC?
The plain-English answer: a PLC is a small rugged computer that runs machines. Where you find them and why they exist.
The scan cycle
How a PLC actually runs your program: read inputs, run program, write outputs — three phases in a loop, dozens of times a second.
Inside the Controller
The memory model, program organisation (tasks + POUs + watchdog), and the IDE project workspace — how the pieces inside a PLC actually fit together.
Ladder logic = relay logic
Why ladder diagrams look like electrical schematics: they ARE electrical schematics, redrawn for a CPU to interpret.
Ladder Logic Basics
Reading and writing your first rungs — contacts, coils, series, and parallel.
NC contacts and stop buttons
Separate physical NC stop contacts from NC ladder instructions, then map healthy-loop and StopPressed tags without inverting the safety intent.
Timers and Counters
TON/TOF/TP timer blocks and CTU/CTD/CTUD counters — side-by-side timing diagrams and a conveyor that demonstrates the rising-edge bug.
The latch (self-holding circuit)
Why a momentary start button can run a motor for hours: the seal-in latch pattern.
Latching and Sealing-In
Build seal-in rungs, use SET/RESET coils deliberately, and make stop-priority behavior predictable when commands overlap.
Timers (TON)
Time-dependent logic with the on-delay timer block. Continuous input for PT seconds → output goes true.
State Machines in Ladder Logic
Model sequential processes with state bits, guarded transitions, and one-shot edges.
Sequential Function Charts
SFC as visual sequencing — steps, transitions, action qualifiers (N/S/P/R), and parallel AND-split / AND-join branches driven by a kinetic chart you can hold-to-advance.
Introduction to Structured Text
ST as Pascal-with-PLC-semantics — variable declarations, IF/ELSIF branches stepped line-by-line, CASE state machines, and the parenthetical function-block call style.
Debugging and the Scan Cycle
Scan-time pitfalls visualised — mid-scan readback, double-write conflicts, and the watchdog timer trip you never want to see in the field.
Analog I/O and Scaling
Live-zero current loops, resistive voltage drop, and the full scale/unscale pipeline — driven by a kinetic 4–20 mA loop scene, a dual-axis linear interpolation visualiser, and a clamping/reverse-acting output demo.
Function Blocks Advanced
Stateless functions vs stateful FB instances; IEC pin layout; TON/CTU lifecycle and edge cases; R_TRIG debouncing; best practices for FB instantiation.
Comparisons and Math
EQ/NEQ/GT/LT/GEQ/LEQ comparison instructions and ADD/SUB/MUL/DIV math — live operand sliders, overflow detection, and a window-comparator scan-order demo.
Shift Registers and Sequencing
Master shift registers for conveyor part tracking and sortation. Watch bits travel cell-by-cell in a kinetic 8-station register, then see a diverter solenoid fire at the exact right moment when the tracked bit arrives.
PID Control Fundamentals
Watch a live PV-response curve chase a setpoint step as you toggle between open-loop, P-only, and full PID — then explore integral windup, anti-windup clamping, bumpless Auto/Manual transfer, and cascade control in an interactive PLC block diagram.
Alarms and Fault Handling
ISA-18.2 alarm state machine — thresholds, ack/reset workflow, first-out latching, alarm shelving, deadband hysteresis, and safe-state design, all driven by live kinetic simulations.
Modbus TCP Advanced
Animated client/server packet exchange, all eight function codes, the four Modbus address spaces, exception responses, and polling strategies.
Safety Systems Introduction
SIL basics, ISO 13849 PL categories, dual-channel cross-monitoring, and a kinetic dual-channel discrepancy latch + E-stop rising-edge reset demo.
Code Organisation
POU types (Program / Function Block / Function), how task scheduling sets scan rates across swim lanes, and global vs local variable scope — all demonstrated with kinetic visuals you can interact with.
Troubleshooting Methodology
Structured fault isolation using decision trees, live watch tables with force simulation, and single-variable change tracking to avoid the most common diagnostic pitfalls.
Reading P&ID symbols
Decode ISA-5.1 instrument bubbles, line types, and tag letters — FT, PT, LT, TT — so you can trace a complete control loop on any P&ID.
Reading electrical schematics
Wire numbers, device designators (CR/M/OL/PB), cross-references, and how to trace a circuit from line diagram to physical panel.
From drawing to I/O list
Build a PLC I/O list from a P&ID and schematic — tag naming rules, address columns, signal type, and the discipline of one-source-of-truth.
Safety circuits 101
Why standard PLC software alone is not an emergency-stop safety function, how ISO 13849-1 categories differ from PL, and how a monitored safety-relay path works.
How a safety relay works
Dual-channel input monitoring, positively driven contacts, reset logic, external-device feedback, and the standard PLC monitoring boundary.
Industrial networks 101
Fieldbus vs Ethernet, what Modbus RTU actually sends, where EtherNet/IP and Profinet fit, and what a junior technician actually needs to know on site.
VFDs for PLC programmers
What a VFD does (V/Hz, ramp times), what the PLC controls (run/stop, speed reference, fault reset), wiring overview, and the parameters you will adjust on a real job.
HMI Principles — Screens Operators Can Actually Use
What an HMI is vs the PLC, sensor-to-PLC-to-HMI data flow, momentary vs latched buttons, pilot lamp colour conventions, numeric displays with engineering units, and the golden rule: interlock logic lives in the PLC, never in the HMI.
Alarm & Colour Design (ISA-101-lite)
Grey-by-default high-performance HMI philosophy, colour reserved for abnormal states, alarm lifecycle (unacknowledged → acknowledged → cleared), why alarm flooding makes alarms invisible, and the overview → unit → detail navigation hierarchy.
Using a multimeter
Use the simulator meter to predict and measure a 24 V DC input, while learning the essential boundary between simulated probing, de-energised continuity tests, and qualified field work.
That wire IS the input
In software you just clicked a simulated button. In real life, that button is wired to the PLC input terminal — and that wire IS what X0 sees.
A sensor is a switch the machine pushes
Real machines use sensors instead of buttons. A photoeye is a switch that closes when something passes through its beam — your program reads it exactly like a button press.
Same logic, different syntax
The same start-stop logic written two ways: ladder (visual) and Structured Text (code). The simulator runs both — pick whichever you prefer.
Reverse-wired NPN photoeye
A photoeye that won't turn the input on. Probe with the meter, find 0 V where you expected 24 V — the photoeye is wired NPN (sinking) when the PLC expects PNP (sourcing). Swap the wires.
Missing PE ground bond
A missing PE bond can prevent sufficient fault current from flowing when a hazardous conductor touches exposed metal. Learn why bonding, disconnection, isolation, and verification all matter.
Wire in the wrong terminal slot
The Start button does nothing. The program looks fine. The wire is in terminal slot 7; the program reads X0 (slot 8). The slot you wire to has to match the address the program reads.
Pull-up resistor on the wrong rail
An open-collector NPN sensor whose pull-up resistor is wired to 0V instead of +24V. The PLC input reads 0V no matter what the sensor does. The pull-up has to pull UP — to +24V.
Loose terminal screw — intermittent input
A Start button works most of the time but randomly fails. Wiggling the wire fixes it. The terminal screw is loose — re-torque it to spec.
Forgotten 0 V return
You wired +24 V into the input but the PLC never reads ON. The 0 V return wire from the PLC back to the supply common is missing — current can't flow, so the input can't respond.
Profinet wiring
Profinet wiring at the cable layer: M12 D-coded vs RJ45 IP20 connectors, daisy-chain vs star vs ring topologies, and the diagnostic LED protocol every Siemens panel speaks.
The Stop button does nothing
The StopPressed tag is FALSE at rest and TRUE when operated, but the rung tests the opposite state. Diagnose the tag semantics before changing the contact instruction.
I can see what's missing
A broken start-stop circuit: motor runs while START is held, drops the moment it's released. The seal-in contact is missing. Once you spot it, you can't un-spot it.
The wire goes nowhere
Press Start — nothing happens. The wiring is fine. The bug is in the program: the rung is reading the wrong input address. The wire and the symbol have to share a name.
The rung that energises nothing
A rung has all the right input contacts but no output. Conditions are met. Nothing happens. Every rung needs something on its right-hand side that DOES something.
The motor runs when it shouldn't
A rung runs the motor backwards: idle when conditions are met, running when they aren't. The bug is an inverted contact at the start of the rung — fix it by removing the slash.
The dryer cycle is over before it started
A 10-second drying cycle finishes in 1 second. The rung looks correct. The bug is a single-character typo in the timer preset value.
Voltage, current, resistance and power
Learn the four quantities behind every electrical fault, solve Ohm's law and the power equation from any two known values, and see why current rather than voltage heats cables.
Series and parallel circuits
Compare one-path and many-path circuits with a lamp bank you can rewire, learn how current, voltage and resistance behave in each, and use that to predict what an open device does.
Reading a simple schematic
Learn to follow a current path on a drawing and recognise the supply, fuse, pushbutton, relay coil and contact, lamp and motor symbols, then prove it by clicking each one.
Control power: 24 V DC or mains
Compare 24 V DC and mains AC for control circuits, work out the current each needs for the same power, and see why plants keep both supplies in one panel.
Meters done safely
Match the meter mode to the question, learn why continuity and resistance are for dead circuits only, and read a voltage pattern to find the open part of a series loop, then practise in the simulator.
Relays and contactors
Separate the coil circuit from the contact circuit, understand normally-open and normally-closed from the coil's point of view, and see how a tiny coil current switches a much larger load.
Motors: single-phase, three-phase and the nameplate
Compare single-phase and three-phase motors, then read a motor nameplate line by line to choose star or delta, find the current to protect against, and estimate speed and efficiency.
Three-phase basics
Relate line and phase voltage with the root-three factor, estimate current for a balanced load, and see in a diagram what a swapped pair of conductors or a lost phase does to a motor.
Overload protection: fuses and breakers
Learn what a fuse, a breaker and a motor overload relay each protect, how a trip curve separates overload from short circuit, and why motors need protection that tolerates starting current.
Grounding and bonding
Understand why the protective earth conductor exists, tell earthing from bonding, and see in a demonstration what a live-to-frame fault does with and without a low-resistance earth path.
Voltage drop and wire gauge
Calculate the voltage a copper cable loses from its length, size and current, see why long 24 V runs need thicker conductors, and explore it with a clearly labelled training calculator.
Capstone: read a three-wire start/stop circuit
Read the standard three-wire motor start and stop control circuit, operate each device in a simulator, and answer graded prediction questions about what happens when each one operates or fails.
Choosing the actuator
VFD, servo, stepper, pneumatic or hydraulic: a short set of questions about what must be controlled, how exactly and with how much force, then a scored decision exercise on eight machine requirements.
Encoders and feedback
How incremental and absolute encoders report position, how quadrature turns printed lines into counts, and how to convert counts to millimetres for a screw or a belt, including the pulse rate a PLC input must cope with.
Motion profiles
The plan for a move as speed against time: trapezoid, triangle for short moves and the S-curve jerk limit, with a live plotter that shows move time, peak speed and shape as you change the sliders.
Homing, limit switches and overtravel
How an axis finds its zero with a home switch and index pulse, the roles of hard stops, hardware limits and software limits, and why limit switches are wired normally closed so a broken wire stops motion.
Pneumatics basics
Air preparation, single- and double-acting cylinders, 3/2 and 5/2 valves drawn in ISO 1219 style and meter-out speed control, with an interactive schematic where you energise a solenoid and watch the air and the piston.
Cylinder sensors and sequencing
Magnetic reed and proximity sensors on cylinders, the A+ B+ B- A- sequence with step bits, and why a sensor-confirmed step with a watchdog timer beats a bare timer, with a step diagram you can run and break.
Hydraulics basics
Pump, relief valve, directional valve, actuator and tank, and the difference between pressure and flow: force follows pressure and area, speed follows flow and area, with a calculator and no maintenance procedures.
Troubleshooting a sticking cylinder or slow axis
A symptom-to-cause drill for slow, sticking, drifting and short-stroking cylinders and for axes that hunt or lose position, starting with what the PLC output and valve indicator say before touching any air or oil.
Capstone: a pick-and-place cycle
Design a sensor-confirmed pick-and-place cycle on paper as a step table of actions, outputs, confirmations and fault reactions, check it in an ordering exercise, then build it in the PLC pick-and-place lab.
What a P&ID is, and what it is not
Read a piping and instrumentation diagram in one pass: name the vessels, pumps, valves and instrument circles, tell a pipe from a signal line, and know what the drawing leaves out.
Instrument tags: reading FIC-101 and friends
Decode ISA-style instrument tags such as FIC-101, LT-204 and PSV-310 letter by letter, understand the loop number, and recognise the idioms and user-choice letters that need the legend.
Following a loop from sensor to valve
Trace a control loop on a P&ID from the transmitter through the controller to the valve, on three diagrams that get harder, ending with a cascade and a separate alarm loop.
Four drawings of the same circuit
Tell apart the schematic, wiring diagram, terminal diagram and panel layout, and learn which question each electrical drawing answers when you are standing at a cabinet.
Labels, terminals and cross-references
Follow a wire number through a drawing set, read terminal references such as X1:4, and use the cross-reference under a coil to find every contact that relay owns.
From P&ID tag to PLC address to terminal
Read a loop diagram from a field transmitter through a junction box and marshalling block to a PLC channel, then fill in the type and channel columns of a mini I/O list.
Cable schedules and field junction boxes
Read a cable schedule row, understand why field cables are gathered in junction boxes with a multicore home run, and use both to find affected loops and spare capacity.
Documenting the PLC program: names, comments, structure
Turn a cryptic rung set into a documented one: function-first tag names, comments that explain why, one writer per output, and the structure and records a handover needs.
Commissioning documents: FAT, SAT, punch lists and as-built drawings
Place FAT, on-site commissioning and SAT in order, learn what each proves, write a useful punch list item and know what an as-built handover package contains.
Troubleshooting from drawings: where do you measure?
Turn a symptom and a schematic into a short list of measurements, use the last-good, first-bad method, and then locate the fault on a graded click-on-drawing exercise.
Stop buttons: the NC contact
The contact with a slash lets power through until its input turns on — exactly what a stop button needs.
The seal-in: a light that holds itself on
Give the output a second path through its own contact and a quick press keeps it running.
Why the seal-in holds: the scan cycle
A PLC reads inputs, runs the rungs, then writes outputs — over and over. That loop is what lets a seal-in remember.
Timers: wait, then switch on
An on-delay timer (TON) turns its Q output on only after its input has stayed on for the preset time.
The plant-floor network stack
Follow one pressure reading from transmitter to ERP, learn what each layer of the plant-floor stack does and what it must never be asked to do, then place real jobs on the right layer.
Fieldbus versus industrial Ethernet
Work out by hand how long a twelve-drive Modbus RTU poll really takes, see why a faster baud rate stops helping, and learn what determinism means for serial buses and switched Ethernet.
Modbus RTU and TCP refresher
Read a Modbus request byte by byte, see exactly what RTU and TCP wrap around the same request, handle the off-by-one trap and exception codes, then decode frames and move on to the graded Modbus labs.
EtherNet/IP and CIP
Follow a conveyor drive through implicit I/O connections and explicit parameter requests, learn the producer/consumer model and the requested packet interval, then choose messaging styles and estimate cyclic network load.
PROFINET: names, roles and GSDML
Understand why a PROFINET controller finds devices by name rather than IP address, learn the controller, device and supervisor roles and the GSDML idea, then fix four classic naming faults in an interactive cabinet rebuild.
OPC UA: servers, nodes and subscriptions
Learn how an OPC UA server describes itself through an address space of nodes, why subscriptions beat polling, and browse a simulated brewery-cellar server to find the right nodes before attempting the graded lab.
MQTT and IIoT: publish, subscribe, topics
How a broker, topics, wildcards, QoS levels, retained messages and last will let many systems share plant data without point-to-point links, with a hands-on wildcard matcher.
OT cyber-security basics: zones, conduits, least privilege
IEC 62443 ideas in plain language: zones and conduits, segmentation, defence in depth, least privilege, default passwords, remote access and why patching a plant differs from patching an office.
SCADA architecture: layers, tags and scan classes
Follow a value from a field transmitter through RTU or PLC, comms, SCADA server, clients and historian, then budget polling load with scan classes versus report by exception.
Trends and historians: deadband, compression, sampling
Why historians compress data, how a deadband can hide a short real event, and how to pick sampling and compression settings, with an interactive trend that loses a spike.
Alarm management: floods, nuisance alarms, rationalisation
ISA-18.2 ideas for a whole plant: alarm floods, root versus consequential and nuisance alarms, rationalisation, priorities and KPIs, plus a rationalisation exercise leading into a free triage lab.
Why machines are guarded
Hazards, harm and the risk-assessment idea from ISO 12100: assess severity and likelihood first, then design out, guard, and only then rely on signs and training. Includes a hazard-ranking exercise.
E-stop circuits
Why emergency stops are normally closed and hard-wired, what stop categories 0, 1 and 2 mean, why buttons carry two channels, and what a reset does and does not do. Ends with a dual-channel wiring lab.
Safety relays and light curtains
Follow a beam break from a light curtain through its two OSSD outputs and a safety relay to the contactors, learn what the relay checks (two channels, forced-guided contacts, contactor feedback, reset), and wire it in a graded lab.
Lockout/tagout
Walk through the lockout/tagout idea on a conveyor belt change: isolate every energy source, lock and tag, release stored energy, verify zero energy with a proven meter, then restore. Sort the steps into order in an interactive checklist.
Electrical hazards
Why the first question on any electrical task is whether it can be done dead: shock, arc flash, the NFPA 70E approach-boundary concepts and the role of PPE as the last line of defence. Concepts only, with no distance tables.
Performance levels and SIL, introduced
Compare a single-switch gate with a dual-channel gate that checks itself, then meet Performance Levels a to e, SIL, and the ingredients behind them (structure, reliability, diagnostic coverage, common cause). Concepts and vocabulary matching only; no calculations.
Machine guarding and interlocks
Fixed guards, interlocked gates with guard locking, two-hand control and presence-sensing devices: how to choose between them by asking how often access is needed and what is still moving. Links to the two-hand control practice scenarios.
Safe PLC programming practices
A standard PLC is not a safety system. Review a start/stop rung for wiring polarity, feedback watchdogs and fault latching, and predict what it does when a stop wire breaks. Links to the motor stop-source, latch and feedback-watchdog scenarios.
Pre-power and commissioning safety checks
The order of a new-machine commissioning day: drawings, inspection, dead tests, a harmless first power-up, staged energising, safety function tests before any motion, and a signed record. Sort the checks into a safe sequence.
The half-split troubleshooting method
Turn a symptom into a path through the circuit, take one measurement at the half-way point, and halve what is left until the fault has nowhere to hide. Worked on a motor that will not start.
Reading the symptoms: LEDs, tags and meter readings
An input LED, an output LED and a voltage reading each prove something different. Learn what each one can and cannot tell you, then read a set of readings to pick the fault location.
Voltage readings you can trust
Set a meter up for a DC voltage reading, name the reference point, understand the category mark on the meter and its leads, and prove a surprising reading before acting on it. Worked through on a supply that looked dead.
Continuity, resistance and current: the other three questions
Learn the three meter jobs that are not a live voltage reading: continuity, resistance and current. See why the first two are dead-circuit tests, how a parallel path fools them, and how a coil is judged against its data sheet and a working twin.
Four fault zones: power, input, program, output
Sort a machine into four fault zones before you measure anything: power side, input side, program side and output side. Ask one first question per zone and use the neighbouring facts to decide where a symptom lives.
Choose your test points from the drawing
Read a schematic for the fault path, mark the reachable test points, write a predicted reading beside each and use a working parallel branch to clear what the branches share. Worked on a mixer that runs in manual and not in auto.
Failure signatures of sensors and actuators
Name the five ways a sensor or actuator misbehaves, read the common signatures of switches, analog loops, coils and valves, and pick the first measurement from the signature. Worked on a tank that reads empty when it is half full.
Intermittent faults: catch it, then find it
Collect the facts around each occurrence, read the pattern, make the machine record the suspects and reproduce the cause safely. Worked on a bottling line that stops on warm afternoons.
One change at a time, then prove the repair
Make one change at a time, put the original back if it did not help, ask why a protective device operated, and prove a repair with the original symptom, a normal cycle and the safety functions restored. Worked on a motor that kept tripping its overload.
Document the fix and hand it over
Write a fault record a colleague can act on, keep the drawing and the program true after a repair, and hand the machine over with its state, its open items and its warnings. Worked on two versions of the same palletiser handover.
Resistors, capacitors and inductors
Decode a resistor colour code, see how a capacitor charges through a resistor, learn why a coil resists changes in current, and set an LED current in your first graded circuit.
Diodes and LEDs
Treat the diode as a one-way valve with a fixed voltage cost, size and power-check an LED current-limiting resistor, and see where the flyback diode protects a coil circuit.
Transistors as switches
Let a weak logic output switch a 12 V lamp or relay coil: size a base resistor with the forced-beta rule, compare NPN, PNP and MOSFET switching, and pass a graded switch-the-lamp challenge.
Logic levels and digital signals
Compare 3.3 V, 5 V and 24 V signalling, test which output can drive which input, learn why industrial inputs use 24 V, and fix a floating switch input with a pull-up.
Analog signals and op-amps
Scale a small sensor voltage with a non-inverting amplifier, see why a follower buffers a weak source, use a comparator to make a yes-or-no from a level, and spot output clipping at the supply rails.
From sensor to signal
Follow a pressure reading onto a 4-20 mA loop and into a 1-5 V input, scale a level with a voltage divider that allows for its load, and smooth noise with an RC filter.
Power supplies
Compare the heat of a linear and a switching regulator on the same 24 V to 5 V job, estimate ripple from the smoothing capacitor, and see why industrial controls standardise on 24 V DC.
Reading datasheets
Tell damage limits from design limits, find the five numbers that decide whether a part suits a job, and practise by clicking the right row on a sample datasheet for a fictional transistor.
Noise, grounding and shielding
Trace where electrical noise starts and how it reaches a signal, then apply twisted pair, shielding, separation and single-point grounding, and match typical noise problems to their fixes.
CircuitPlayground: build, check, learn
Apply nodal analysis to a small circuit by hand, then build and check six graded circuits (LED, divider, pull-up, transistor switch) in a tap-to-place explorer that is a training model, not a SPICE simulator.
PCB and soldering basics
Learn what a printed circuit board is, compare through-hole and surface-mount parts, put the stages of a good solder joint in order, and review the fume, heat and static precautions.
Electronics troubleshooting
Use voltage measurements and divide-and-conquer to find a dark LED fault, then answer a graded set that maps symptoms to causes for LEDs, transistor switches, inputs, noise and 4-20 mA loops.
Force, torque and work in plain language
Torque is a force with a lever, work is force times distance, and the two are not the same thing: learn both with a unit-aware calculator in SI and imperial.
Speed, power and efficiency
Power is torque times speed, and efficiencies in series multiply: work through rpm, kW and hp conversions and see how much of the input power reaches the load.
Gears and gearboxes
A gear ratio trades speed for torque: build a gear train by choosing tooth counts and read the output speed, torque and direction, including a compound two-stage reducer.
Belts, chains and pulleys
Pulley and sprocket ratios, belt speed, wrap angle and slip: compute a belt drive and decide when a V-belt, timing belt or chain is the right choice.
Shafts, keys and couplings
How keys, set screws and couplings carry torque, why rigid and flexible couplings differ, and how to tell angular, parallel and axial misalignment apart from a picture.
Bearings and lubrication
Ball, roller and plain bearings, how to read a bearing number, sealed versus greasable designs, and the noise and heat clues that show a bearing is failing.
Inertia and acceleration
Why a motor needs time to speed up a heavy load: torque equals inertia times acceleration, inertia reflects through a gearbox by the ratio squared, and a hands-on demo shows acceleration time as the load changes.
Linear motion: ball screws, rack and pinion, guides and belts
Lead is travel per turn: turn screws, racks and belts into speed, thrust and encoder resolution, and see why guides, backlash and gravity matter on a real axis.
Reading mechanical drawings
Orthographic views, line types, dimensions and tolerances, plus a first look at geometric tolerance symbols with a tolerance checker and an identify-the-symbol exercise.
Fasteners and thread basics
Bolts, screws, studs and washers, how to decode a thread and a bolt grade, and why torque specs and thread-lockers exist, with no tightening values and a pointer to the manufacturer tables.
Alignment, vibration and condition clues
What noise, heat and vibration tell you about a machine: place a vibration peak as a multiple of running speed, learn the classic suspects, and see why trending beats one-off readings.
Mechanical troubleshooting
A safe, structured method for mechanical faults and a graded symptom-to-likely-cause quiz set covering belts, couplings, bearings, gearboxes, lubrication and drive trips.
