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TPFP Technicien Maintenance Industrielle practice questions

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Question 1Maintenance diagnosis, condition evidence and controlled restoration

Over a six-month observation period (total operating time T = 4,320 hours), an automated coil slitting line experienced 12 unscheduled breakdown stoppages. What is the Mean Time Between Failures (MTBF) and the corresponding failure rate (λ)?

  1. MTBF = 360 hours; λ ≈ 0.00278 failures/hour (2.78 × 10⁻³) Correct answer.
  2. MTBF = 12 hours; λ = 0.083 failures/hour
  3. MTBF = 51,840 hours; λ ≈ 0.000019 failures/hour
  4. MTBF = 360 days; λ = 2.78 failures/hour

Explanation

Under standard reliability definitions (AFNOR NF EN 13306): MTBF = Total Operating Time / Number of Failures = 4,320 hours / 12 = 360 hours. The failure rate λ is the reciprocal of MTBF: λ = 1 / MTBF = 1 / 360 ≈ 0.00278 failures per operating hour.

Question 2Maintenance diagnosis, condition evidence and controlled restoration

During the same six-month period on the coil slitting line, the cumulative downtime spent on active corrective repairs across all 12 breakdowns totaled 42 hours. What is the Mean Time To Repair (MTTR), which serves as the key indicator of equipment maintainability?

  1. MTTR = 0.29 hours
  2. MTTR = 3.5 hours Correct answer.
  3. MTTR = 42.0 hours
  4. MTTR = 7.0 hours

Explanation

Under AFNOR NF EN 13306: MTTR = Total Corrective Maintenance Time / Total Number of Corrective Actions = 42 hours / 12 repairs = 3.5 hours per breakdown. MTTR directly measures the maintainability of the installation and efficiency of technician troubleshooting.

Question 3Maintenance diagnosis, condition evidence and controlled restoration

In the supplied simplified availability model A=MTBF/(MTBF+MTTR), use450hours and4.5hours. What value results, excluding other logistical or scheduled delays?

  1. Ao = 90.00%
  2. Ao = 95.50%
  3. Ao = 99.01% Correct answer.
  4. Ao = 99.90%

Explanation

Operational availability is calculated using the standard reliability formula Ao = MTBF / (MTBF + MTTR) = 450 / (450 + 4.5) = 450 / 454.5 ≈ 0.9901 (99.01%). This means the rolling stand is operational and capable of production 99.01% of its scheduled operating time.

Question 4Maintenance diagnosis, condition evidence and controlled restoration

A maintenance progress group performs an AMDEC Machine (FMEA) on an automated robotic welding cell. For the failure mode 'welder positioner drive belt snapped', the team assigns: Gravity G = 4 (severe production stoppage > 4 h), Occurrence F = 3 (frequency ~once every 2 months), Non-Detection D = 3 (detected only after bad parts are produced). The plant policy mandates technical corrective action when Criticality C ≥ 30. What is the calculated Criticality Index C and what conclusion is drawn?

  1. C = G × F × D = 4 × 3 × 3 = 36; because C exceeds the threshold of 30, the progress group must design and implement a technical improvement (such as installing a non-contact inductive speed monitoring sensor to drop D to 1) Correct answer.
  2. C = G + F + D = 10; because 10 < 30, no action is required and the failure is accepted
  3. C = 4 × 3 = 12; Non-detection is never factored into AMDEC calculations
  4. C = 433; the plant must be immediately decommissioned

Explanation

For the supplied scoring model, 4×3×3=36, which exceeds its stated internal threshold30. The result triggers the specified review, not proof that a particular sensor makes the risk acceptable. Confirm appropriate safety controls and validate any change through competent engineering assessment.

Question 5Maintenance diagnosis, condition evidence and controlled restoration

Operators on an automated sheet bending press occasionally insert asymmetrical stamped blanks backward into the die, causing punch collisions and tooling damage. The maintenance technician proposes a Poka-Yoke (système anti-erreur / détrompeur) technical improvement. Which solution exemplifies a true Poka-Yoke?

  1. Placing a warning sign on the press guard instructing operators to pay closer attention
  2. Adding an asymmetrical locating guide pin (détrompeur mécanique) or optical profile sensor in the die nesting plate that physically prevents backward insertion or inhibits press cycle start if the blank orientation is incorrect Correct answer.
  3. Increasing the press speed by 50% so operators have less time to think
  4. Imposing financial fines on operators who misfeed parts

Explanation

A Poka-Yoke (mistake-proofing) is a mechanism that either makes it physically impossible to make a mistake (mechanical keying/asymmetric pin) or detects an error immediately and shuts down the operation before damage occurs (profile sensor interlock). Signs, warnings, and administrative penalties rely on human vigilance and do not constitute Poka-Yoke.

Question 6Maintenance diagnosis, condition evidence and controlled restoration

A maintenance team launches a 5S continuous improvement project in the central mechanical overhaul shop. Which pillar of the 5S methodology focuses specifically on 'Sorting' (Seiri / Débarrasser) by identifying, tagging, and removing all obsolete tools, scrap parts, and unnecessary equipment from the workspace?

  1. Seiton (Set in order / Ranger)
  2. Seiso (Shine / Nettoyer)
  3. Seiketsu (Standardize / Standardiser)
  4. Seiri (Sort / Débarrasser / Éliminer l'inutile) Correct answer.

Explanation

Seiri (Sort) is the 1st step of 5S: distinguishing between necessary and unnecessary items, red-tagging obsolete or broken equipment, and removing them from the work environment. Seiton organizes what remains, Seiso cleans, Seiketsu standardizes, and Shitsuke sustains.

Question 7Maintenance diagnosis, condition evidence and controlled restoration

As part of an Industry 4.0 predictive maintenance modernization, the maintenance department equips critical high-speed gearbox bearings with connected IO-Link condition monitoring sensors. What two physical variables are most effectively measured together in a single compact IO-Link sensor to track bearing mechanical health and early lubrication distress?

  1. Ambient relative humidity and barometric air pressure
  2. Surface contact temperature and broadband high-frequency vibration velocity/acceleration (RMS and peak) Correct answer.
  3. Optical color tint and electrical static charge
  4. Ambient sound volume in dBA and magnetic flux

Explanation

Modern industrial IIoT condition monitoring sensors (e.g. IO-Link vibration/temperature sensors from IFM, Balluff, or Banner) combine a triaxial MEMS accelerometer (measuring vibration velocity RMS for unbalance/misalignment and acceleration peak for bearing impact severity) with an integrated contact RTD/thermistor (measuring raceway thermal rise), providing complete condition tracking via digital fieldbus.

Question 8Maintenance diagnosis, condition evidence and controlled restoration

On a continuous billet cooling bed, technicians must grease 32 individual bearing pillow blocks located beneath high-temperature radiation covers, requiring line shutdowns and safety lockouts. What technical modification dramatically improves maintainability, grease consistency, and technician safety?

  1. Instruct operators to stop greasing the bearings entirely
  2. Replace all bearings with wood blocks soaked in diesel fuel
  3. Install an automated centralized progressive grease lubrication system (graissage centralisé progressif) with a single external pump, metering distributor blocks, and an electrical cycle switch connected to the PLC/GMAO Correct answer.
  4. Remove the radiation covers and grease bearings manually while the red-hot steel billets pass by

Explanation

Automated centralized progressive lubrication systems distribute measured, precise micro-doses of grease to every bearing point at regular operating intervals without requiring human access into hazardous, hot zones. A cycle monitoring switch on the progressive metering valve verifies positive lubricant delivery and alerts the PLC/GMAO if a line blocks.

Question 9Maintenance diagnosis, condition evidence and controlled restoration

In a lean manufacturing facility, what is the specific function of an 'Andon' visual management system installed along an automated coil processing line?

  1. An automated camera that photographs workers during lunch breaks
  2. A financial software tool used exclusively by human resources
  3. An electronic lock that traps operators at their workstations during breakdowns
  4. A visual and acoustic signaling system (light towers, display boards, audible chimes) that immediately alerts maintenance, production, and quality teams to a stoppage, safety hazard, or abnormal operating state in real time Correct answer.

Explanation

Originating in the Toyota Production System, an Andon is a visual control tool that empowers operators and automated machines to signal production anomalies, equipment faults, or material shortages instantly via color-coded light stacks and overhead boards. This minimizes response latency and accelerates maintenance technician dispatch.

Question 10Maintenance diagnosis, condition evidence and controlled restoration

A continuous metallurgy fume extraction fan operates 8,000 hours per year at rated 30 kW mechanical shaft load. The maintenance team replaces a burned-out IE1 standard motor (efficiency η1 = 90.7%) with a premium IE3 efficiency motor (η3 = 93.6%). Given an electricity tariff of 0.15 €/kWh, what is the annual electrical energy saved and the resulting financial savings?

  1. ~8,200 kWh/year saved, resulting in approximately 1,230 € in annual electricity cost reduction Correct answer.
  2. ~250 kWh/year saved, resulting in 37.50 € in annual savings
  3. ~24,000 kWh/year saved, resulting in 3,600 € in annual savings
  4. Zero savings, because both motors deliver the exact same 30 kW mechanical shaft power

Explanation

Electrical power consumed with IE1: P1 = 30 kW / 0.907 ≈ 33.076 kW. Electrical power consumed with IE3: P3 = 30 kW / 0.936 ≈ 32.051 kW. Electrical power saved = 33.076 - 32.051 = 1.025 kW. Annual energy savings = 1.025 kW × 8,000 h = 8,200 kWh/year. Annual financial cost reduction = 8,200 kWh × 0.15 €/kWh = 1,230 €/year.

Question 11Maintenance diagnosis, condition evidence and controlled restoration

Under the Autonomous Maintenance pillar (Maintenance Autonome - Jishu Hozen) of Total Productive Maintenance (TPM), what is the primary role assigned to production machine operators?

  1. Operators are trained to rewire high-voltage electrical substations
  2. Operators dismantle and rebuild hydraulic piston pumps on workshop benches
  3. Operators perform routine daily cleaning, lubrication, visual inspections, minor fastener tightening, and Level 1 checks to detect abnormalities early and prevent forced deterioration Correct answer.
  4. Operators are strictly forbidden from touching machines or cleaning chips

Explanation

Autonomous-maintenance concepts can involve appropriately trained operators in designated routine checks and basic care. The actual tasks, isolation needs, authority and competence limits must be defined by the equipment and site procedures. It is not permission for every operator to lubricate, tighten or repair any running machine.

Question 12Maintenance diagnosis, condition evidence and controlled restoration

A maintenance technician participates in a 'Kaizen' workshop on a rolling mill finishing line. What is the fundamental philosophy and approach of Kaizen in industrial maintenance?

  1. Completely demolishing and rebuilding the manufacturing plant every two years
  2. Continuous, incremental improvement involving all shop-floor personnel (operators, technicians, supervisors) directly at the gemba (workplace) to eliminate waste (muda) and enhance equipment reliability with low capital investment Correct answer.
  3. Terminating the employment of technicians whose machines experience breakdowns
  4. Outsourcing all maintenance decisions exclusively to remote software algorithms

Explanation

Kaizen (from the Japanese words for 'change' and 'good') is a philosophy of continuous, incremental improvement. It engages cross-functional teams directly on the shop floor (gemba) to eliminate waste (muda), streamline workflows, improve ergonomics, and enhance machine reliability using practical, low-cost solutions rather than expensive overhauls.

Question 13Measurement, feedback, PLC and automation

A three-phase 400 V (line-to-line, 50 Hz) asynchronous motor drives an industrial centrifugal pump. The motor delivers a mechanical shaft power of 7.5 kW with an efficiency (η) of 0.88 and a power factor (cos φ) of 0.82. What is the line current (I) drawn by the motor under rated load?

  1. 15.0 A Correct answer.
  2. 10.8 A
  3. 26.0 A
  4. 8.7 A

Explanation

Total electrical active power consumed is P_elec = P_mech / η = 7,500 W / 0.88 ≈ 8,522.7 W. Using the three-phase power formula P_elec = √3 × U × I × cos φ, line current is I = 8,522.7 / (√3 × 400 × 0.82) = 8,522.7 / 568.17 ≈ 15.0 A.

Question 14Measurement, feedback, PLC and automation

What is the primary operational function and operating principle of a bimetallic thermal overload relay (relais thermique bilame) installed beneath a contactor in a motor starter?

  1. Protects the motor against prolonged small overcurrents and phase loss using bimetallic strips that bend when heated Correct answer.
  2. Protects the motor and cables against instantaneous high-magnitude short-circuit currents using magnetic solenoids
  3. Regulates motor speed by altering the frequency of the AC voltage waveform supplied to the stator
  4. Measures insulation resistance to ground and disconnects power when leakage current exceeds 30 mA

Explanation

A thermal overload relay contains three bimetallic strips heated directly or indirectly by the motor current. Under sustained moderate overcurrent or single-phasing, differential thermal expansion bends the strips to trip auxiliary contacts (95-96 NC opens to de-energize the contactor coil). It does not provide magnetic short-circuit protection.

Question 15Measurement, feedback, PLC and automation

When diagnosing an industrial 24 V DC control circuit with a digital multimeter, how must the test leads be connected to measure voltage across an inductive sensor output, and how must they be connected to measure loop current?

  1. Voltmeter in parallel across the component terminals; ammeter in series by breaking the circuit loop Correct answer.
  2. Voltmeter in series within the circuit loop; ammeter in parallel across the power supply terminals
  3. Both voltmeter and ammeter in parallel across the sensor terminals simultaneously
  4. Both voltmeter and ammeter in series inserted into the power supply ground conductor

Explanation

A voltmeter has very high internal impedance (> 10 MΩ) and must be placed in parallel across the component to measure potential difference without drawing significant current. An ammeter has near-zero internal impedance and must be inserted in series into an opened circuit branch; connecting an ammeter in parallel causes a dead short-circuit.

Question 16Measurement, feedback, PLC and automation

In a traditional star-delta (étoile-triangle) electromechanical starter for a 400 V / 690 V three-phase motor, how do the starting current (I_start) and starting torque (T_start) in star connection compare to direct-on-line (DOL) delta starting values?

  1. Both starting current and starting torque are divided by 3 (reduced to approximately 33% of direct starting values) Correct answer.
  2. Starting current is divided by 3, while starting torque remains 100% of nominal starting torque
  3. Starting current is divided by √3 (reduced to 58%), while starting torque is divided by 3
  4. Both starting current and starting torque are divided by √3 (reduced to approximately 57.7%)

Explanation

In star connection, the voltage across each phase winding is reduced from line voltage U to phase voltage V = U / √3 (a factor of 1/√3). Because winding impedance is constant, phase current is divided by √3, and line current is therefore divided by √3 × √3 = 3. Because electromagnetic torque is proportional to the square of the voltage (T ∝ V²), starting torque is also reduced by (1/√3)² = 1/3.

Question 17Measurement, feedback, PLC and automation

What is the function of installing a freewheeling flyback diode (diode de roue libre) or RC snubber suppressor in reverse parallel across an industrial 24 V DC pneumatic solenoid valve coil?

  1. Clamps high-voltage inductive back-EMF spikes (e = -L·di/dt) generated when the coil is de-energized, protecting PLC output transistors and relay contacts Correct answer.
  2. Speeds up the collapse of the coil's magnetic field so the valve spool returns to its rest position faster
  3. Provides short-circuit current limiting to prevent the coil from drawing more than 10 mA of holding current
  4. Smooths the PWM ripple of the PLC transistor output so the coil sees a steady DC holding voltage

Explanation

An inductor resists changes in current. When a PLC transistor switches off a 24 V DC solenoid, the collapsing magnetic field produces a high-voltage reverse inductive kick (e = -L di/dt) that can reach hundreds of volts, destroying the transistor. A reverse-biased flyback diode provides a circulating loop to safely dissipate this energy as current.

Question 18Measurement, feedback, PLC and automation

What is the defining electrical characteristic of the TN-S earthing system (schéma de liaison à la terre TN-S) widely utilized in French industrial plant distribution?

  1. The transformer neutral is grounded at the substation, and the Neutral (N) and Protective Earth (PE) conductors are kept strictly separated throughout the entire installation Correct answer.
  2. The transformer neutral is isolated from ground (impedant), allowing the plant to continue running on a first insulation fault
  3. The Neutral and Protective Earth functions are combined into a single PEN conductor all the way to individual machines
  4. Each individual machine has its own independent ground rod with no connection to the transformer neutral ground

Explanation

In a TN-S system (T = Terre at source, N = Neutral bonded to earth, S = Séparé), the source neutral is solidly earthed at the HV/LV transformer. The neutral conductor (N) and protective earth conductor (PE) are routed as completely separate conductors throughout the installation. An insulation fault becomes a phase-to-PE short-circuit cleared rapidly by overcurrent protective devices.

Question 19Measurement, feedback, PLC and automation

In a conventional hardwired direct-on-line motor starter control circuit, what is the role of the auxiliary normally open contact (contact NO 13-14) wired in parallel with the momentary start pushbutton (bouton poussoir marche S2)?

  1. Maintains coil energization (auto-maintien / holding circuit) after the operator releases the momentary start pushbutton Correct answer.
  2. Provides instant thermal overload tripping if the motor stalls during initial acceleration
  3. Powers the green panel pilot indicator lamp in series with the emergency stop pushbutton
  4. Interlocks with the reverse contactor to prevent simultaneous phase-to-phase short-circuits

Explanation

Because a start pushbutton has momentary spring-return contacts, it opens as soon as the operator releases it. The auxiliary NO contact (terminals 13-14 of contactor KM1) wired in parallel across the start pushbutton closes when KM1 pulls in, latching the supply circuit to the coil (l'auto-maintien) until a stop pushbutton (S1) or overload contact (95-96) opens.

Question 20Measurement, feedback, PLC and automation

Which listed exhaust-path defect is a plausible hypothesis to investigate for sluggish pneumatic cylinders despite a normal upstream pressure reading?

  1. Sintered bronze exhaust silencers on the directional control valves are clogged with oil residue and particulates, creating high exhaust backpressure Correct answer.
  2. The FRL lubricator bowl has run dry, so the valve spools and cylinder seals are working without oil mist
  3. The main pressure regulator diaphragm has ruptured and downstream working pressure has collapsed to about 2 bar
  4. The magnetic reed position sensors on the cylinders have drifted, so the PLC records the strokes as incomplete

Explanation

Pneumatic silencers (silencieux d'échappement) screwed into ports 3 and 5 of directional valves collect atomized oil, pipe scale, and ambient dust over time. When clogged, exhausting air cannot escape rapidly, building up opposing backpressure in the non-working cylinder chamber and dramatically slowing actuator motion.

Question 21Measurement, feedback, PLC and automation

A 4-pole three-phase induction motor connected to a 50 Hz electrical network has a full-load rotor speed of n = 1,440 rpm. What is the synchronous speed (n_s) of the rotating stator magnetic field, what is the motor slip (g), and what is the electrical frequency of the currents induced in the rotor bars (f_r)?

  1. n_s = 1,500 rpm; slip g = 4.0%; rotor frequency f_r = 2.0 Hz Correct answer.
  2. n_s = 3,000 rpm; slip g = 8.0%; rotor frequency f_r = 4.0 Hz
  3. n_s = 1,440 rpm; slip g = 0.0%; rotor frequency f_r = 50.0 Hz
  4. n_s = 1,000 rpm; slip g = -4.0%; rotor frequency f_r = 25.0 Hz

Explanation

Synchronous speed for a p = 2 pole-pair motor at f = 50 Hz is n_s = (60 × f) / p = (60 × 50) / 2 = 1,500 rpm. Slip is g = (n_s - n) / n_s = (1,500 - 1,440) / 1,500 = 60 / 1,500 = 0.04 (4.0%). The induced rotor frequency is f_r = g × f = 0.04 × 50 Hz = 2.0 Hz.

Question 22Measurement, feedback, PLC and automation

Given the supplied unequal phase currents and nameplate current, which listed observation and authorized diagnostic path is supported rather than simply increasing the protection setting?

  1. Marked phase-current unbalance with Phase 3 above nameplate current; check supply voltage balance, terminal tightness and contactor contacts, then measure the three winding resistances Correct answer.
  2. Normal mechanical overload of the driven machine; reduce the process throughput and reset the relay
  3. The relay is simply set too low; raise the dial to 16.5 A so that the highest measured phase no longer trips it
  4. A measurement artefact; the clamp meter was closed around a cable containing all three conductors, so the readings are meaningless

Explanation

Two phases sit near 12 A while the third carries 16.5 A, well above the 14 A nameplate value. A bimetallic relay heats on the highest phase and, on relays fitted with a differential mechanism, unbalance also accelerates the trip. Unbalanced currents on a healthy supply point to added resistance in one path (loose terminal, pitted contactor contact, damaged conductor) or to a winding fault, so the diagnosis is to check supply voltage balance and connections and then compare the three winding resistances.

Question 23Pneumatic and hydraulic model reasoning

An industrial air preparation FRL unit at the pneumatic entry of an automated production cell consists of three modular components in series. What are these three components?

  1. Filtre (filter), Régulateur / Détendeur (pressure regulator), and Lubrificateur (lubricator) Correct answer.
  2. Filtre (filter), Sécheur frigorifique (refrigerant dryer), and Réservoir tampon (air receiver)
  3. Régulateur (regulator), Clapet anti-retour (non-return valve), and Silencieux d'échappement (exhaust silencer)
  4. Flexible (hose), Raccord (fitting), and Manomètre (pressure gauge)

Explanation

An FRL unit is the standard air preparation assembly comprising a 5–40 μm particle and condensate Filter (filtre avec purge), an adjustable diaphragm Pressure Regulator (régulateur/détendeur) with pressure gauge, and an oil-mist Lubricator (lubrificateur, where air-tool lubrication is required).

Question 24Pneumatic and hydraulic model reasoning

In pneumatic machine automation, what distinguishes a 5/2 monostable directional control valve from a 5/2 bistable directional control valve?

  1. A monostable valve returns to its rest position by a mechanical spring when pilot signal is removed, while a bistable valve remains in its last switched position Correct answer.
  2. A monostable valve controls double-acting cylinders, while a bistable valve can only control single-acting cylinders
  3. A monostable valve requires two separate pilot signals to switch, while a bistable valve switches automatically via internal fluid pressure
  4. A monostable valve has 5 positions and 2 ports, whereas a bistable valve has 2 positions and 5 ports

Explanation

In pneumatic nomenclature, a 5/2 valve has 5 ports and 2 switching positions. A monostable valve has one command signal (solenoid or air pilot) and an opposing mechanical spring return (rappel par ressort) that forces the spool back to rest when de-energized. A bistable valve has two command signals (impulse memory) and stays in its last active state until the opposing signal fires.

Question 25Pneumatic and hydraulic model reasoning

Which statement accurately describes an industrial double-acting pneumatic cylinder (vérin double effet)?

  1. It has two air supply ports and produces controllable pneumatic thrust during both the extension stroke and the retraction stroke Correct answer.
  2. It has only one air supply port and utilizes an internal coil spring to execute the return stroke
  3. It has two air ports but develops exactly the same force on both strokes, because the two piston faces have identical areas
  4. It develops thrust only on extension and relies on the weight of the load or an external force to bring the rod back

Explanation

A double-acting cylinder (vérin double effet) features two pneumatic ports (one rear cap port, one front rod port). Applying air pressure to the rear extends the piston rod while exhausting the front; applying air to the front retracts the rod while exhausting the rear, generating power in both linear directions.

Question 26Pneumatic and hydraulic model reasoning

A double-acting pneumatic cylinder has a piston bore diameter of D = 63 mm. The workshop compressed air network supplies an effective gauge pressure of 6.0 bar (0.6 MPa) to the cylinder rear port. Neglecting frictional losses, what is the theoretical pushing force (effort de poussée) developed by the cylinder on extension?

  1. 1,870 N Correct answer.
  2. 187 N
  3. 7,480 N
  4. 18,700 N

Explanation

Piston radius is r = 63 mm / 2 = 31.5 mm = 3.15 cm. Piston surface area is S = π × r² = π × (3.15)² ≈ 31.17 cm² (or 3.117 × 10⁻³ m²). With pressure p = 6.0 bar = 6.0 × 10⁵ Pa = 6.0 daN/cm², theoretical thrust force is F = p × S = (6.0 × 10⁵ N/m²) × (3.117 × 10⁻³ m²) ≈ 1,870 N (or 187 daN).

Question 27Pneumatic and hydraulic model reasoning

A double-acting pneumatic cylinder with a piston bore diameter D = 63 mm has a piston rod diameter d = 20 mm. Operating at a working pressure of 6.0 bar (0.6 MPa), what is the theoretical pulling force (effort de traction) developed during the retraction stroke?

  1. 1,682 N Correct answer.
  2. 1,870 N
  3. 188 N
  4. 872 N

Explanation

During retraction, air acts only on the annular area: S_annular = (π / 4) × (D² - d²) = (π / 4) × (6.3² - 2.0²) cm² = (π / 4) × (39.69 - 4.00) = (π / 4) × 35.69 ≈ 28.03 cm² = 2.803 × 10⁻³ m². The theoretical pulling force is F_pull = p × S_annular = (6.0 × 10⁵ N/m²) × (2.803 × 10⁻³ m²) ≈ 1,682 N.

Question 28Pneumatic and hydraulic model reasoning

In the stated conventional double-acting pneumatic-cylinder example, why can meter-out flow control improve speed stability compared with unrestricted exhausting?

  1. Meter-out creates an air backpressure cushion in the exhausting chamber that prevents jerky stick-slip movements and stabilizes speed under varying loads Correct answer.
  2. Meter-out consumes half as much compressed air from the compressor network compared to meter-in control
  3. Meter-out lets a single one-way flow control valve regulate both the extension and the retraction speed, halving the component count
  4. Meter-in cannot physically be implemented on a double-acting cylinder because each port alternates between supply and exhaust

Explanation

Restricting the exhausting path can provide a stabilizing backpressure in a suitable pneumatic circuit. The actual load, pressure, components and control design determine performance. A generic flow restrictor is not a universal safe holding device, and neither meter-out nor meter-in is the best solution for every application.

Question 29Pneumatic and hydraulic model reasoning

In a pneumatic two-hand safety control circuit (commande bimanuelle), a dual-pressure valve (sélecteur à deux pressions / cellule ET) is installed. What is the operational logic of this valve, and what happens if one input receives 4.0 bar while the second input receives 6.0 bar simultaneously?

  1. The valve functions as an AND gate; output air is delivered only when both inputs are pressurized, and the lower pressure (4.0 bar) is routed to the output Correct answer.
  2. The valve functions as an OR gate; output air is delivered if either input is pressurized, routing the higher pressure (6.0 bar) to the output
  3. The valve vents all air to atmosphere whenever the input pressures differ by more than 0.5 bar
  4. The valve combines both pressures to deliver an intensified output of 10.0 bar to the cylinder

Explanation

A dual-pressure valve (cellule ET / AND gate) has a sliding spool with two seats. If only one port is pressurized, the spool slides to block that port. When both ports are pressurized, the higher pressure (6.0 bar) forces the spool against the opposite seat, allowing the lower pressure (4.0 bar) to pass through to the output port 2.

Question 30Pneumatic and hydraulic model reasoning

What fundamental physical principle forms the basis of all industrial hydraulic power transmission systems (Pascal's Law)?

  1. Pressure exerted on a confined, incompressible fluid is transmitted equally and undiminished in all directions throughout the fluid Correct answer.
  2. Fluid flow velocity increases proportionally with the square of the pipe diameter
  3. The volume of a gas decreases as its absolute temperature increases at constant pressure
  4. Frictional head loss in a pipe is independent of fluid viscosity and flow regime

Explanation

Pascal's Law states that a change in pressure applied to an enclosed, static, incompressible fluid is transmitted undiminished to every portion of the fluid and to the walls of its container, enabling hydraulic systems to multiply force (F = p × A).

Question 31Pneumatic and hydraulic model reasoning

Where is the primary pressure relief valve (limiteur de pression principal) located in an industrial hydraulic power unit (centrale hydraulique), and what is its essential function?

  1. Installed on a tee immediately downstream of the hydraulic pump discharge, opening to reservoir when system pressure reaches the preset maximum limit Correct answer.
  2. Installed inside the return line filter to prevent oil from returning to the tank when the filter is clean
  3. Installed in the suction line between the reservoir and the pump inlet, so that excess pressure is relieved before it reaches the pump
  4. Installed on the reservoir breather, to relieve tank pressure as the oil warms up and expands

Explanation

The main pressure relief valve (limiteur de pression) is piped directly off the pump pressure line. It acts as the primary safety device by remaining normally closed; when load resistance causes circuit pressure to reach the relief setting (e.g. 210 bar), the internal poppet lifts against a calibrated spring to bypass excess flow safely back to the reservoir.

Question 32Pneumatic and hydraulic model reasoning

An industrial hydraulic power pack supplies a constant flow rate of Q = 24.0 L/min to extend a double-acting clamping cylinder with a bore diameter D = 80 mm. Neglecting internal leakage, what is the linear extension speed (v) of the piston rod?

  1. 7.96 cm/s (approximately 0.080 m/s) Correct answer.
  2. 15.9 cm/s (approximately 0.160 m/s)
  3. 4.77 m/s
  4. 1.99 cm/s

Explanation

Piston radius is r = 40 mm = 4.0 cm = 0.04 m. Piston surface area is A = π × r² = π × (0.04)² ≈ 0.005027 m² = 50.27 cm². Flow rate in m³/s is Q = (24.0 × 10⁻³ m³) / 60 s = 0.0004 m³/s (or 400 cm³/s). Linear speed is v = Q / A = 400 cm³/s / 50.27 cm² ≈ 7.96 cm/s = 0.0796 m/s.

Question 33Pneumatic and hydraulic model reasoning

A fixed-displacement hydraulic pump delivers a flow rate of Q = 30.0 L/min at an operating circuit pressure of p = 210 bar. Using standard industrial units, what is the theoretical hydraulic power (P_hyd) produced by the fluid stream?

  1. 10.5 kW Correct answer.
  2. 63.0 kW
  3. 3.5 kW
  4. 6.3 kW

Explanation

In industrial hydraulics, hydraulic power is calculated directly using the practical formula P_hyd (kW) = [p (bar) × Q (L/min)] / 600. Substituting: P_hyd = (210 × 30.0) / 600 = 6,300 / 600 = 10.5 kW. (Alternatively in SI: P = p × Q = 21 × 10⁶ Pa × 0.0005 m³/s = 10,500 W = 10.5 kW).

Question 34Pneumatic and hydraulic model reasoning

An external gear pump driven by an electric motor rotating at n = 1,450 rpm delivers an actual flow rate of Q = 43.5 L/min at low pressure with an assumed volumetric efficiency of 100%. What is the geometric displacement (cylindrée V_g) of the pump per revolution?

  1. 30.0 cm³/rev (cm³/tr) Correct answer.
  2. 15.0 cm³/rev
  3. 43.5 cm³/rev
  4. 0.030 cm³/rev

Explanation

Displacement is calculated by V_g = [Q (L/min) × 1,000 cm³/L] / n (rpm). Substituting the values: V_g = (43.5 × 1,000) / 1,450 = 43,500 / 1,450 = 30.0 cm³/revolution.

Question 35Pneumatic and hydraulic model reasoning

Which listed mechanism can produce the supplied pump rattling, pitting and fluctuating pressure when inadequate suction conditions allow local liquid pressure to fall below vapor pressure?

  1. Cavitation (cavitation): excessive suction vacuum causes dissolved vapor bubbles to form and violently collapse against metal surfaces Correct answer.
  2. Thermal degradation: the oil is running too hot, so the film breaks down and the gear flanks scuff against the housing
  3. Over-pressurisation: the main relief valve has been set above the pump's rated pressure, crushing the gears against their bearings
  4. Electro-erosion: shaft currents from the variable-speed drive are discharging through the pump's bearings and shaft

Explanation

Under the supplied low-local-pressure condition, vapor cavities form and can collapse as pressure recovers, causing noise and damage. This is cavitation, distinct from simply drawing free air into a suction line. Actual evidence and operating conditions must be assessed rather than diagnose every noisy pump identically.

Question 36Pneumatic and hydraulic model reasoning

How does an electro-hydraulic proportional directional control valve (distributeur proportionnel) differ in operation from a standard on/off solenoid directional control valve?

  1. It uses variable proportional solenoids to continuously adjust spool position and orifice opening, providing progressive control over flow rate, acceleration, and deceleration Correct answer.
  2. It offers three fixed flow settings (slow, medium, fast) selected by three separate on/off solenoids
  3. It regulates circuit pressure rather than flow, and cannot change the direction of the actuator
  4. It is pilot-operated and needs a minimum pilot pressure of about 210 bar before the spool will move at all

Explanation

Standard directional valves are on/off devices with binary positions (open or closed). Proportional valves utilize proportional solenoids controlled by variable electrical current (e.g. 0–10 V or 4–20 mA converted to coil PWM). The spool position is continuously adjustable, enabling controlled velocity ramps, soft starting, and variable positioning without hydraulic shock.

Question 37Pneumatic and hydraulic model reasoning

What is the primary function of an in-line hydraulic counterbalance valve (valve d'équilibrage / clapet parachute) mounted directly to the port of a vertical hoist hydraulic cylinder?

  1. Supports suspended loads to prevent free-fall in the event of hose rupture and enables smooth, controlled lowering by requiring pilot pressure to open Correct answer.
  2. Increases lifting speed by routing rod-side oil back into the piston side of the same cylinder (regenerative connection)
  3. Caps the maximum pressure the cylinder can see, protecting its seals and end caps from over-pressure
  4. Locks the suspended load mechanically with a spring-applied friction clamp gripping the piston rod

Explanation

An appropriately selected and engineered counterbalance arrangement can control an overrunning load and support load holding under its design conditions. Installation position, leakage, component failure, load pressure and protective requirements matter. Naming a counterbalance valve alone does not prove that every hose failure or suspended-load hazard is controlled.

Question 38Pneumatic and hydraulic model reasoning

For a supplied ideal lossless regenerative cylinder circuit, the rod-end discharge joins full-bore inlet flow during extension. With pump flow Q_p and rod cross-sectional area A_r, what is the model velocity?

  1. v_reg = Q_p / A_r (speed is determined solely by pump flow divided by the cross-sectional area of the piston rod) Correct answer.
  2. v_reg = Q_p / A_p (speed is identical to standard cylinder extension)
  3. v_reg = Q_p / (A_p + A_r) (speed is substantially slower than conventional extension)
  4. v_reg = Q_p × A_p / A_r² (speed increases exponentially with pressure squared)

Explanation

In a regenerative circuit, the fluid expelled from the rod end (Q_rod = [A_p - A_r] × v) joins the pump flow Q_p to enter the piston cap: Q_total = Q_p + Q_rod = A_p × v. Rearranging: Q_p + (A_p - A_r) × v = A_p × v, which simplifies directly to Q_p = A_r × v, hence v_reg = Q_p / A_r. This yields a much faster rapid-traverse speed at reduced thrust force.

Question 39Pneumatic and hydraulic model reasoning

What is the core operating principle of a Load-Sensing (LS) variable-displacement axial piston pump system in an industrial automated machine?

  1. A pilot line senses highest actuator working pressure and adjusts pump swashplate displacement to supply only the demanded flow at a constant margin pressure above load pressure Correct answer.
  2. The pump runs at maximum displacement continuously, discharging all unconsumed fluid across a high-pressure relief valve to generate heat
  3. The pump swashplate is mechanically linked to the machine emergency stop button to vent oil only when an operator enters the cell
  4. The pump senses electrical power consumption from the factory substation and shuts down during peak utility tariff hours

Explanation

A Load-Sensing (LS) system feeds back the highest actuator load pressure (P_load) to the pump displacement compensator. The pump swashplate adjusts its angle so that pump delivery pressure is maintained at exactly P_pump = P_load + ΔP_margin (where ΔP_margin is typically 15–25 bar). This eliminates massive throttling heat losses and maximizes energy efficiency.

Question 40Machine assembly, metrology, bearings and power transmission

When mechanically cold-mounting a deep-groove ball bearing onto a solid cylindrical shaft with an interference fit, how must mounting force be applied to prevent damaging the bearing?

  1. Apply mounting force strictly to the inner ring using a mounting sleeve and dead-blow mallet, never transmitting force through the rolling elements Correct answer.
  2. Apply force directly to the outer ring face to squeeze the balls firmly into the raceway grooves
  3. Hammer directly against the sheet steel ball cage (cage de guidage) until the bearing seats against the shoulder
  4. Apply the force to whichever ring is easier to reach, since an interference fit spreads the load evenly through the whole bearing

Explanation

For the stated inner-ring interference fit, appropriate mounting force should act through the inner ring under the approved method, not through rolling elements. Actual tooling and fit instructions determine how this is achieved. The choice identifies the load path, not permission to strike a bearing or improvise unsafe mounting.

Question 41Machine assembly, metrology, bearings and power transmission

What standard maintenance tool and method should a technician use to verify and set the correct tension on an industrial V-belt (courroie trapézoïdale) drive?

  1. Use an acoustic belt tension meter (mesureur de fréquence vibratoire) or spring-loaded deflection tester to measure natural frequency or force-deflection ratio Correct answer.
  2. Tension the drive until the belt can just be twisted 90° by hand at mid-span, then lock the motor base
  3. Increase the centre distance until the motor's measured running current rises by about 10% above its no-load value
  4. Tighten the taper-lock bush of the driven pulley to the manufacturer's torque figure, which sets the belt tension

Explanation

Precise belt tensioning is measured either by an optical/acoustic tension meter that reads the natural vibrational frequency (Hz) of the belt strand when plucked, or a mechanical spring gauge that measures the force required to produce a specific deflection (typically about 1.5 mm per 100 mm of span, checked against the manufacturer's force table).

Question 42Machine assembly, metrology, bearings and power transmission

What does the viscosity grade 'ISO VG 46' indicate on a drum of industrial mineral hydraulic oil?

  1. The oil has a nominal kinematic viscosity of 46 mm²/s (cSt) at a standardized reference temperature of 40 °C Correct answer.
  2. The oil has a nominal kinematic viscosity of 46 mm²/s (cSt) measured at 100 °C
  3. The oil has a dynamic (absolute) viscosity of 46 mPa·s (cP) at 40 °C
  4. The oil has a viscosity index (VI) of 46, describing how much its viscosity changes with temperature

Explanation

Under the international ISO 3448 classification, the ISO Viscosity Grade (VG) number designates the fluid's mid-point kinematic viscosity in centistokes (cSt or mm²/s) measured at standard test temperature 40.0 °C (with allowable tolerance ± 10%, i.e. 41.4 to 50.6 mm²/s for VG 46).

Question 43Machine assembly, metrology, bearings and power transmission

What is the primary function of an elastomeric jaw coupling (accouplement élastique à mâchoires / flector) positioned between an electric motor shaft and a gearbox input shaft?

  1. Transmits torque while accommodating minor parallel, angular, and axial shaft misalignments and damping torsional vibration shocks Correct answer.
  2. Acts as a torque limiter whose spider shears at a preset value to protect the gearbox from overload
  3. Acts as a permanent rigid solid connection that prevents any relative movement whatsoever between shafts
  4. Absorbs large axial thermal growth of up to about 10 mm between the motor and the gearbox

Explanation

Flexible elastomeric couplings (e.g. spider couplings / accouplements à flector en polyuréthane) bridge drive shafts to transmit rotational torque while absorbing slight residual misalignments (up to 0.5–1° angular, 0.2–0.4 mm radial) and isolating drive electronics from sudden shock loads.

Question 44Machine assembly, metrology, bearings and power transmission

A two-stage parallel shaft speed reducer has a first stage pinion with Z1 = 18 teeth driving gear Z2 = 54 teeth, and a second stage pinion with Z3 = 20 teeth driving output gear Z4 = 80 teeth. If the input motor rotates at n_in = 1,440 rpm, what is the output shaft speed (n_out) and overall reduction ratio (i)?

  1. Overall ratio i = 12.0:1; output speed n_out = 120 rpm Correct answer.
  2. Overall ratio i = 7.0:1; output speed n_out = 205 rpm
  3. Overall ratio i = 4.0:1; output speed n_out = 360 rpm
  4. Overall ratio i = 24.0:1; output speed n_out = 60 rpm

Explanation

Stage 1 ratio is i1 = Z2 / Z1 = 54 / 18 = 3.0. Stage 2 ratio is i2 = Z4 / Z3 = 80 / 20 = 4.0. Total gear reduction ratio is the product of the individual stages: i_total = i1 × i2 = 3.0 × 4.0 = 12.0. The output speed is n_out = n_in / i_total = 1,440 rpm / 12.0 = 120 rpm.

Question 45Machine assembly, metrology, bearings and power transmission

For the stated conventional single radial lip seal used to retain gearbox oil, which listed orientation follows its intended retained-fluid side, subject to the actual manufacturer’s instructions?

  1. The sealing lip and internal garter spring must face toward the fluid media to be retained so that internal fluid pressure presses the lip tighter against the shaft Correct answer.
  2. The sealing lip must face toward the outside air to prevent atmospheric dust from contacting the shaft
  3. The garter spring must be removed with pliers before installation to reduce friction torque
  4. The seal must be installed completely dry with no lubricant on the sealing lip or shaft surface

Explanation

A radial lip seal is pressure-energized. The sealing lip containing the circular garter spring must face the fluid reservoir (inward). Internal fluid pressure acts under the lip, pressing it tighter against the rotating shaft. The lip must be pre-lubricated with clean operating grease/oil to prevent burn-up during initial dry startup.

Question 46Machine assembly, metrology, bearings and power transmission

When the specified motor and fit design calls for a C3-clearance bearing, which listed thermal/fit consideration can explain that selection rather than substituting it universally?

  1. To compensate for the reduction in internal radial clearance caused by shaft thermal expansion and heavy shaft interference fits during operation Correct answer.
  2. To allow the shaft to be fitted with a clearance fit instead of an interference fit, so the bearing can be changed without a puller
  3. To raise the load rating of the bearing, because a larger clearance spreads the load over more rolling elements
  4. To loosen the dimensional precision tolerances on the raceways and rolling elements, which lowers the purchase price

Explanation

When a bearing is pressed onto a shaft with an interference fit (m5/k5), the inner ring expands, taking up a portion of the internal clearance. Furthermore, rotor heat from the motor shaft expands the inner ring faster than the outer ring cools in the housing. A C3 clearance provides greater initial radial gap so that under full operating temperature, running clearance is optimal (near zero).

Question 47Machine assembly, metrology, bearings and power transmission

An electric motor delivers an output mechanical power of P = 11.0 kW to a conveyor drive shaft rotating at a steady speed of n = 1,450 rpm. What is the nominal output torque (C in N·m) transmitted through the shaft coupling?

  1. 72.4 N·m Correct answer.
  2. 144.8 N·m
  3. 7.59 N·m
  4. 159.5 N·m

Explanation

Angular velocity is ω = 2π × n / 60 = (2 × π × 1,450) / 60 ≈ 151.84 rad/s. Torque is calculated from power and angular velocity using P = C × ω, so C = P / ω = 11,000 W / 151.84 rad/s ≈ 72.44 N·m. (Alternatively, using the practical formula C = 9,550 × P (kW) / n (rpm) = 9,550 × 11.0 / 1,450 ≈ 72.45 N·m).

Question 48Measurement, feedback, PLC and automation

During a daily machine inspection, a maintenance technician observes that the differential pressure indicator (indicateur de colmatage) on the high-pressure hydraulic line filter has popped up its red visual button. What action must the technician take?

  1. Schedule immediate replacement of the filter cartridge before fluid bypasses unfiltered contaminants into sensitive proportional valves Correct answer.
  2. Reset the indicator button with a screwdriver and continue running until the pump stops building pressure
  3. Increase the main pressure relief valve setting by 50 bar to push through the restriction
  4. Top up the reservoir with fresh oil of the same grade, since the clogging indicator responds to a low fluid level

Explanation

A filter restriction indication warrants assessment under the actual flow, temperature and manufacturer’s criteria rather than ignoring the condition. Appropriate safe replacement or other action depends on that assessment and the actual circuit. No live housing opening or universal immediate-change threshold is prescribed here.

Question 49Measurement, feedback, PLC and automation

What is the primary electrical function of optocouplers (optocoupleurs) incorporated on the digital input cards of an industrial Programmable Logic Controller (API / PLC)?

  1. Provides complete galvanic isolation between noisy external 24 V DC field wiring and sensitive internal microprocessor logic circuitry Correct answer.
  2. Filters mechanical contact bounce, replacing the input card's configurable hardware input filter
  3. Converts the 24 V field level down to the 3.3 V CPU level, which is why no separate input conditioning stage is needed
  4. Multiplexes several field inputs onto one CPU line so that a 16-channel card only needs four internal connections

Explanation

An optocoupler transfers an appropriate signal across an optical isolation barrier, helping separate the specified field and logic circuits. Actual module ratings and construction define its insulation and common arrangements. It does not make every external condition harmless or replace required electrical protection and safe work procedures.

Question 50Measurement, feedback, PLC and automation

According to French and European standard NF EN 60848 for GRAFCET (Sequential Function Chart), when is a transition considered 'cleared' (franchie)?

  1. When all immediately preceding steps connected to the transition are active, AND the associated transition receptivity condition evaluates to TRUE Correct answer.
  2. Whenever the machine operator presses the green illuminated cycle start pushbutton, regardless of active steps
  3. Automatically every 50 milliseconds based on the internal PLC system clock
  4. Only when all steps in the entire GRAFCET chart have simultaneously turned off

Explanation

Rule 2 of standard NF EN 60848 states that a transition is validated (validée) when all immediately preceding steps are active. A transition is cleared (franchie) if and only if it is validated AND its associated receptivity (réceptivité / logical condition) is true. Clearing the transition simultaneously deactivates preceding steps and activates succeeding steps.