ITI Technician Mechatronics (AITT Theory) cheat sheet

Lockout/tagout sequence: notify, shut down, isolate all energy sources, dissipate stored energy (bleed hydraulics, discharge capacitors, block suspended loads), lock and tag, verify zero energy by test.

Electrical shock severity depends on current through the body: about 1 mA is perception threshold, 10-30 mA causes muscle tetany (cannot let go), 50-100 mA can cause ventricular fibrillation; body resistance drops sharply when skin is wet.

Arc flash boundary is the distance at which incident energy equals 1.2 cal/cm2 (second-degree burn threshold); PPE category is selected from the calculated incident energy, not from voltage alone.

Fire classes and extinguishers: A ordinary combustibles (water, foam), B flammable liquids (foam, CO2, dry powder), C energized electrical (CO2, dry powder, never water), D metals (special dry powder).

Machine guarding rule: guards must prevent access to the point of operation and be interlocked so that removing the guard stops hazardous motion before a person can reach the danger zone.

Permit-required confined space entry requires atmospheric testing (O2 19.5-23.5 percent, LEL below 10 percent, H2S/CO within limits) before entry, continuous monitoring, an attendant outside, and a rescue plan.

Safe manual handling: keep the load close to the body, lift with legs, avoid twisting while loaded; two-person lift when the load exceeds about 25 kg or the shape is awkward.

Hydraulic systems store energy in accumulators: depressurize and isolate the accumulator (close the isolating valve, drain the gas side per procedure) before breaking any line; fluid jets can penetrate skin.

Hierarchy of controls, most to least effective: elimination, substitution, engineering controls (guarding, ventilation, enclosure), administrative controls (procedures, rotation), PPE last.

Local exhaust ventilation captures contaminant at the source; check capture velocity at the hood face, not airflow at the fan, because duct leaks and blockages reduce face velocity.

Noise exposure: 85 dB(A) is the common 8-hour action level; an increase of 3 dB halves the permitted exposure time (exchange rate), so 88 dB(A) allows 4 hours.

Hazardous waste segregation: never mix waste streams (e.g., solvents with aqueous waste); used oil, spent coolant, batteries, and electronic waste each go to separate labelled containers with a manifest.

SDS (Safety Data Sheet) sections give the key data: section 2 hazards, section 4 first aid, section 6 spill measures, section 8 exposure limits and PPE, section 13 disposal.

Spill response order: alert and evacuate, stop the source if safe, contain with absorbent or a dike, ventilate, collect into labelled containers, decontaminate, report and record.

Electrical and electronic waste handling: discharge and remove capacitors and batteries before recycling, and treat CRTs and fluorescent tubes as hazardous (mercury) waste.

Ergonomic risk factors at a mechatronics workstation: repetitive motion, sustained awkward posture, high force, contact stress, and vibration; reduce by adjusting bench height, tool weight, and task rotation.

First-angle projection: the view is placed on the far side of the object (object between observer and plane); third-angle: the view is placed on the near side. Symbol shows a truncated cone; third-angle has the small circle drawn on the left.

Line conventions: continuous thick = visible edges, dashed = hidden edges, chain thin = centre lines and pitch circles, continuous thin = dimension and projection lines, wavy = break lines.

Dimensioning rules: dimensions state true size regardless of drawing scale; place them on the view that shows the feature true shape; never dimension the same feature twice; do not dimension to hidden lines if avoidable.

ISO fits on drawings are written as nominal size plus tolerance class, e.g. 40 H7/g6; H marks a hole basis, h a shaft basis; the letter gives the fundamental deviation and the number the IT grade.

Section views: hatching at 45 degrees shows cut material; adjacent parts are hatched in opposite directions; shafts, bolts, and pins cut longitudinally are conventionally left unsectioned.

Geometric tolerancing symbols: flatness and straightness need no datum; perpendicularity, parallelism, and angularity reference a datum; position uses a feature control frame with tolerance, symbol, and datums in order.

Surface roughness Ra is the arithmetic mean deviation in micrometres; lower Ra means a smoother surface; the surface texture symbol places the machining allowance and Ra value relative to the symbol.

Assembly drawings carry a bill of materials with item number, part number, description, and quantity; each part is identified by balloon numbers matching the BOM.

Tolerance = upper limit minus lower limit. For a hole, deviation is measured from the lower limit; for a shaft, from the upper limit. Fundamental deviation sets the nearest limit to the zero line.

Fit types: clearance (hole minimum larger than shaft maximum), interference (shaft minimum larger than hole maximum), transition (limits overlap, may be either).

Hole-basis system: hole lower deviation is zero (H); shaft letters a to g give clearance, h gives line-to-line, j to n transition, p to zc interference.

Maximum and minimum clearance = hole max minus shaft min, and hole min minus shaft max; interference equivalent = shaft max minus hole min.

Micrometer reading = main barrel scale + thimble division x least count. A 0.01 mm thimble with 50 divisions gives 0.01 mm per division; read to 0.001 mm with a vernier on the sleeve.

Vernier caliper: least count = main scale division minus vernier scale division; typical 0.02 mm with 50 vernier divisions on a 1 mm main scale.

Measurement errors: Abbe error (measurement axis not in line with scale), cosine error (misalignment), parallax, temperature (steel expands about 11.5 x 10^-6 per degree C), and instrument zero error.

Gauge selection: a plug gauge checks hole size (go/no-go), a snap gauge checks shaft; a gauge must be calibrated against a traceable standard and checked for wear.

Ohm's law V = I x R; power P = V x I = I^2 R = V^2 / R. In series, current is common and resistances add; in parallel, voltage is common and conductances add.

Three-phase power: P = sqrt(3) x V_line x I_line x power factor for a balanced load; star connection gives V_line = sqrt(3) x V_phase, delta gives I_line = sqrt(3) x I_phase.

Kirchhoff's laws: current law, sum of currents at a node is zero; voltage law, sum of voltages around a closed loop is zero.

Diode: forward drop about 0.7 V for silicon, 0.3 V for germanium; reverse biased it blocks. A bridge rectifier converts AC to pulsating DC; a capacitor filter smooths it.

Transistor as a switch: NPN conducts when base is about 0.7 V above emitter (saturated); base resistor limits base current to I_C / hFE.

Capacitor impedance Xc = 1 / (2 pi f C); inductor impedance Xl = 2 pi f L; at resonance in series RLC, Xl = Xc and impedance is minimum (equal to R).

Logic gates: AND outputs 1 only when all inputs are 1; OR outputs 1 when any input is 1; NAND and NOR are universal gates; XOR outputs 1 when inputs differ.

Continuity and insulation testing: de-energize and prove dead before resistance tests; a megger measures insulation resistance, typically at 500 V DC, and readings in megohms indicate healthy insulation.

Thread notation M10 x 1.5 means metric coarse (or fine) thread, nominal diameter 10 mm and pitch 1.5 mm; pitch = 1 / threads per inch for inch threads.

Bolt preload is set by torque T = K x F x d, where K is the nut factor (about 0.2 dry, 0.15 lubricated), F the clamp force, d the nominal diameter.

Bearing life L10 = (C / P)^p x 10^6 revolutions, where C is dynamic load rating, P the equivalent load, p = 3 for ball bearings and 10/3 for roller bearings.

Key and keyway transmit torque by shear and crushing; a Woodruff key suits light loads, a parallel key drives heavier loads, a taper key resists reversal.

Springs: Hooke's law F = k x; springs in parallel add stiffness, springs in series combine as 1/k = 1/k1 + 1/k2.

Gear ratio = number of teeth on driven gear divided by teeth on driver; torque multiplies by the ratio while speed divides by it (ignoring losses).

Shaft alignment: coupling misalignment shows as vibration at 1x and 2x running speed; use dial indicators or laser alignment and correct angular before parallel offset.

Seals: O-rings seal by controlled squeeze (typically 15-25 percent of cross-section); lip seals need a film of oil and correct shaft surface finish to avoid leakage.

Belt drives: velocity ratio = D1 / D2 = N2 / N1; belt length for an open drive L = 2C + pi(D1 + D2)/2 + (D2 - D1)^2 / (4C).

V-belt drives transmit more torque than flat belts because of wedge action in the groove; they must run in matched sets and correct tension (about 1-2 percent elongation).

Chain drives: pitch and number of teeth set the ratio; keep slack on the return side, lubricate per speed, and check for elongation above about 1.5 percent pitch.

Gear trains: overall ratio is the product of individual stage ratios; an idler changes direction only; a worm drive gives high reduction and self-locking at low lead angles.

Clutches and brakes: torque capacity depends on friction coefficient, clamping force, and mean radius; a slip clutch limits torque to protect the drivetrain.

Couplings: rigid couplings need accurate alignment; flexible couplings tolerate small misalignment; a fluid coupling slips at start and limits starting torque.

Shaft speed and power: P = 2 pi N T / 60, so torque T = 9550 x P(kW) / N(rpm) in newton-metres.

Critical speed of a shaft occurs at the natural frequency; running near it causes large vibration, so operating speed is kept well away (typically below 75 percent of critical).

Pascal's law: pressure applied to a confined fluid is transmitted equally in all directions. Force F = p x A; a larger piston area multiplies force but reduces stroke speed for the same flow.

Flow continuity: Q = A x v. For a given pump flow, a smaller bore gives a faster extension; rod-end and cap-end areas differ, so extend and retract speeds differ.

Hydraulic power P = p x Q (watts with p in Pa and Q in m3/s); in practical units kW = p(bar) x Q(L/min) / 600.

Relief valve limits system pressure and protects the pump; set it about 10-15 percent above working pressure. A pressure-reducing valve limits downstream pressure, not system pressure.

Directional control valve notation: number of positions / number of ways (e.g., 5/2); centre condition of a 4/3 valve (closed, tandem, float, open) determines pump unloading and actuator drift.

Pneumatic air preparation: filter, regulator, lubricator in that order; FRL unit; pressure set by the regulator, and a drain trap removes condensate.

Cylinder cushioning slows the piston near end of stroke by trapping exhaust oil or air through an adjustable needle; flow control valves meter speed, pressure valves limit force.

Fluid maintenance: contamination is the main cause of hydraulic failure; keep oil at the specified ISO cleanliness class, change filters, and check for air ingress causing spongy operation and cavitation.

Sensor vs transducer: a sensor detects a physical quantity; a transducer converts one form of energy to another; a transmitter outputs a standardized signal (4-20 mA, 0-10 V).

4-20 mA loop: 4 mA represents the zero or live zero, which allows broken-wire detection; loop resistance must satisfy the transmitter's compliance voltage.

RTD (Pt100) resistance rises with temperature, about 0.385 ohm per degree C near 0 C; thermocouple generates a small voltage (mV) from the Seebeck effect and needs cold-junction compensation.

Strain gauge: gauge factor GF = (delta R / R) / (delta L / L); a Wheatstone bridge converts small resistance changes into a measurable voltage.

Inductive proximity sensor detects metal only; capacitive detects most materials including liquids; both have a sensing range and a hysteresis; shielded versions allow flush mounting.

Encoder resolution: pulses per revolution x 4 with quadrature decoding gives counts per revolution; an incremental encoder needs homing, an absolute encoder reports position after power-up.

Instrument accuracy terms: accuracy is closeness to true value, precision is repeatability; span error and zero error are corrected by calibration; resolution is the smallest detectable change.

Load cell wiring: four-wire (excitation +, excitation -, signal +, signal -) with a shielded cable; output is typically 2 mV/V at rated load, so a 10 V excitation gives 20 mV full scale.

PLC scan cycle: read inputs into the input image table, execute the program top to bottom, update outputs from the output image table, then housekeeping and communications; scan time is typically 1-20 ms.

Sourcing vs sinking: a sinking input module provides the return path (common positive); a sourcing input supplies positive voltage. Match sensor type (PNP sources current, NPN sinks) to the module.

Ladder logic: XIC (examine if closed) and XIO (examine if open) are contacts; OTE is an output coil; OTL/OTU latch and unlatch; a latch keeps state after the input drops.

Timers: TON on-delay (accumulates while true), TOF off-delay, RTO retentive; counters CTU count up on false-to-true transitions and are reset by RES.

PID control: proportional output acts on present error, integral removes steady-state offset, derivative damps rate of change; too much gain causes oscillation, too much integral causes overshoot and windup.

Open versus closed loop: open loop has no feedback and cannot correct disturbance; closed loop compares feedback to setpoint and acts on the error.

Safety functions belong in a safety PLC or hardwired safety relay, not in standard logic; the safety circuit must be independent of the standard control program.

Analog scaling: scaled value = ((raw - raw_min) / (raw_max - raw_min)) x (eng_max - eng_min) + eng_min; 4-20 mA on a 0-27648 range maps 0-100 percent.

DC motor speed: N proportional to (V - I R) / flux. Field weakening raises speed with reduced torque; armature voltage control gives constant torque below base speed.

Three-phase induction motor synchronous speed Ns = 120 f / p; slip s = (Ns - N) / Ns, typically 2-5 percent at full load; torque is proportional to square of applied voltage.

V/f control keeps flux constant below base speed; above base speed field weakening reduces torque. A VFD ramps frequency and voltage to limit starting current.

Motor starting: direct-on-line draws 5-8 times rated current; star-delta reduces starting current to one third of DOL and starting torque to one third.

Stepper motor: step angle = 360 / (steps per revolution); microstepping increases resolution but reduces torque per step; open-loop control can lose steps if overloaded.

Servo motor with encoder closes the position loop; tuning gains (position, velocity, integral) determine response; excessive gain causes oscillation and noise.

Single-phase induction motors are not self-starting; a capacitor or split-phase winding provides starting torque; a capacitor-run motor uses a permanent run capacitor.

Protection: thermal overload relay protects the motor from sustained overcurrent; fuses and breakers protect cables; earth leakage protection (RCD) protects people.

System boundary and interface definition: mechanical, electrical, pneumatic, and software interfaces must be documented (signal type, range, connector, protocol) before integration.

Signal levels and compatibility: 24 V DC industrial I/O, 4-20 mA analog, 0-10 V analog, RS-485/Modbus, Ethernet/IP or PROFINET; level shifting or isolation is required when mixing.

Grounding and shielding: single-point ground for analog signals, shield grounded at one end to avoid ground loops; separate power and signal cables to reduce noise.

Commissioning sequence: mechanical alignment check, electrical continuity and insulation check, dry-run without load, then load test with limits and interlocks verified.

Interlock and safety validation: verify every E-stop, guard switch, and light curtain stops hazardous motion and requires a manual reset before restart.

Bus diagnostics: check termination resistors at both ends of a fieldbus, node addresses, baud rate match, and cable length limits before blaming the program.

Handshake logic between PLC and robot: use request/ready/busy/done bits with timeout monitoring so a lost signal does not hang the cell.

Documentation set: P&ID, electrical schematics, I/O list, network layout, and as-built drawings updated after any change.

Robot degrees of freedom equal the number of independent joints; a 6-axis articulated robot can position and orient the tool in 3D space; fewer axes restrict orientation.

Workspace and singularities: at a wrist singularity axes align and joint speeds become very high; avoid programming straight-line motion through singular points.

Coordinate frames: joint, world, tool (TCP), and user frames; a tool centre point offset must be taught accurately or all programmed paths shift.

SCARA robots have two revolute joints in a horizontal plane plus a vertical prismatic axis; they suit fast pick-and-place with limited vertical stiffness.

Teach pendant programming: point-to-point (joint) motion is fastest but path is uncontrolled; linear and circular motion control the path but are slower.

End effectors: vacuum grippers suit flat, non-porous parts; two-finger grippers need stroke and force matched to the part; compliance (RCC) helps insertion tasks.

Safety: robot safety standards require risk assessment, safeguarding (fences, light curtains, area scanners), and reduced speed or torque limits for collaborative operation.

Repeatability versus accuracy: repeatability is the spread of repeated returns to the same point; accuracy is closeness to the commanded point; robots are usually more repeatable than accurate.

Troubleshooting order: gather symptoms, verify the fault, isolate by half-splitting (divide the system and test each half), identify root cause, correct, then verify and record.

Five whys and fishbone (Ishikawa) diagrams separate symptom from cause; causes are grouped as man, machine, material, method, measurement, environment.

Preventive maintenance is time-based; predictive (condition-based) maintenance uses vibration, thermography, oil analysis, and motor current signature to schedule work before failure.

Vibration analysis: unbalance shows 1x radial, misalignment 2x axial, looseness many harmonics, bearing defects at high-frequency non-synchronous peaks (BPFO/BPFI).

Thermography finds loose connections, overloaded conductors, and bearing overheating; compare similar phases and load conditions.

Electrical fault finding: check supply voltage, fuses and breakers, then control circuit continuity; a PLC input LED off with a good sensor indicates wiring or module fault, not the sensor.

Hydraulic/pneumatic fault finding: check pressure at the gauge, flow at the actuator, leakage, and valve spool movement; a slow cylinder often indicates a clogged filter or internal bypass.

Failure records: log downtime, symptom, cause, action, and spare used; MTBF = total operating time / number of failures; MTTR = total repair time / number of repairs.

Robot degrees of freedom equal the number of independent joints; a 6-axis articulated robot can position and orient the tool in 3D space; fewer axes restrict orientation.

Workspace and singularities: at a wrist singularity axes align and joint speeds become very high; avoid programming straight-line motion through singular points.

Coordinate frames: joint, world, tool (TCP), and user frames; a tool centre point offset must be taught accurately or all programmed paths shift.

SCARA robots have two revolute joints in a horizontal plane plus a vertical prismatic axis; they suit fast pick-and-place with limited vertical stiffness.

Teach pendant programming: point-to-point (joint) motion is fastest but path is uncontrolled; linear and circular motion control the path but are slower.

End effectors: vacuum grippers suit flat, non-porous parts; two-finger grippers need stroke and force matched to the part; compliance (RCC) helps insertion tasks.

Safety: robot safety standards require risk assessment, safeguarding (fences, light curtains, area scanners), and reduced speed or torque limits for collaborative operation.

Repeatability versus accuracy: repeatability is the spread of repeated returns to the same point; accuracy is closeness to the commanded point; robots are usually more repeatable than accurate.