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Question 1Technik (fachliche Inhalte des Faches Technik)

In an open-loop control system (Steuerung), which statement describes the relationship between the controlled variable and the manipulated variable?

  1. The controlled variable is continuously measured and compared with a reference value.
  2. The controller adjusts the manipulated variable until the error becomes zero.
  3. The manipulated variable is set without measuring the controlled variable, so disturbances are not corrected. Correct answer.
  4. The system always returns to its setpoint after a disturbance.

Explanation

Open-loop control follows a fixed sequence of commands and does not feed back any measurement of the output. Because there is no comparison between actual and desired value, disturbances act on the output without being corrected. Feedback and error correction are characteristics of closed-loop control.

Question 2Technik (fachliche Inhalte des Faches Technik)

A DC motor draws 4 A at 24 V. Assuming ideal conversion, what mechanical power does it deliver?

  1. 60 W
  2. 96 W Correct answer.
  3. 6 W
  4. 28 W

Explanation

Electrical power equals voltage multiplied by current, so P = 24 V × 4 A = 96 W. With ideal conversion, all of this electrical power becomes mechanical output. The other values come from adding or dividing the given quantities instead of multiplying them.

Question 3Technik (fachliche Inhalte des Faches Technik)

Which sensor principle converts a mechanical force directly into an electrical signal by changing its resistance?

  1. Strain gauge (Dehnungsmessstreifen) Correct answer.
  2. Hall effect sensor
  3. Inductive proximity sensor
  4. Photodiode

Explanation

A strain gauge is a resistive element whose length and cross-section change under mechanical load, altering its resistance. This resistance change is proportional to strain and therefore to applied force. The other sensors respond to magnetic fields or light rather than to mechanical deformation.

Question 4Technik (fachliche Inhalte des Faches Technik)

In a CNC program, what does the G-code word G01 command?

  1. Circular interpolation in a clockwise direction
  2. Linear interpolation at a defined feed rate Correct answer.
  3. Rapid positioning at maximum machine speed
  4. Tool change to the next tool in the magazine

Explanation

G01 selects linear interpolation, and the machine moves along a straight line at the feed rate set by an F word. Rapid traverse without cutting is G00, which is a different command. Circular interpolation and tool change use other G-codes.

Question 5Technik (fachliche Inhalte des Faches Technik)

Why is a freewheel diode (Freilaufdiode) placed in parallel with an inductive load such as a relay coil?

  1. It protects the coil against excessive ambient temperature.
  2. It provides a path for the induced current so the voltage spike at switch-off is limited. Correct answer.
  3. It rectifies the supply voltage so the coil receives direct current.
  4. It increases the coil current during operation to hold the relay more firmly.

Explanation

When current through an inductor is interrupted, the collapsing magnetic field induces a voltage that can destroy the switching transistor. The freewheel diode, connected in reverse bias during normal operation, offers a path for the decaying current. This limits the induced voltage to roughly the diode's forward voltage.

Question 6Technik (fachliche Inhalte des Faches Technik)

A gear pair has a driving gear with 20 teeth and a driven gear with 60 teeth. What is the transmission ratio and how does the output speed compare with the input speed?

  1. Ratio 3:1, output speed is three times input speed
  2. Ratio 1:3, output speed is one third of input speed
  3. Ratio 3:1, output speed is one third of input speed Correct answer.
  4. Ratio 1:3, output speed is three times input speed

Explanation

The ratio of a gear pair is the driven tooth count divided by the driving tooth count, here 60/20 = 3. Speed is inversely proportional to tooth count, so the larger driven gear turns one third as fast. Torque increases by the same factor of three.

Question 7Technik (fachliche Inhalte des Faches Technik)

Which statement correctly describes the difference between a thermocouple and a resistance temperature detector (RTD)?

  1. Both devices output a digital signal proportional to temperature.
  2. A thermocouple produces a voltage from the Seebeck effect, while an RTD changes resistance with temperature. Correct answer.
  3. A thermocouple requires an external excitation current, while an RTD does not.
  4. A thermocouple changes resistance with temperature, while an RTD produces a voltage.

Explanation

A thermocouple relies on the Seebeck effect: two dissimilar metals joined at a measuring point generate a small voltage proportional to the temperature difference. An RTD uses a metal such as platinum whose resistance rises predictably with temperature. Both are analogue sensors, not digital.

Question 8Technik (fachliche Inhalte des Faches Technik)

What is the main function of a Programmable Logic Controller (PLC) in an automated machine?

  1. It mechanically transmits torque from the motor to the machine axis.
  2. It converts three-phase mains power into a regulated DC bus voltage.
  3. It stores the finished workpieces between two production steps.
  4. It reads input signals, executes a stored control program, and drives outputs. Correct answer.

Explanation

A PLC samples digital and analogue inputs, runs a cyclic user program stored in memory, and sets its outputs accordingly. This makes it the central controller of a machine sequence. Power conversion, torque transmission and buffering are tasks of other components.

Question 9Technik (fachliche Inhalte des Faches Technik)

In a closed-loop control circuit, what does the transfer element with the largest time constant mainly determine?

  1. The steady-state accuracy of the sensor
  2. The mechanical stiffness of the frame
  3. The speed of response of the whole loop Correct answer.
  4. The colour of the status display

Explanation

The dominant time constant of a loop sets how quickly the output can follow a change in the reference value. It therefore largely determines the achievable settling time and the bandwidth. Steady-state accuracy depends mainly on controller gain and integral action, not on the dominant time constant.

Question 10Technik (fachliche Inhalte des Faches Technik)

A hydraulic cylinder has a piston area of 20 cm² and is supplied with oil at 100 bar. What force does the piston produce?

  1. 20 kN Correct answer.
  2. 2 kN
  3. 0.2 kN
  4. 200 kN

Explanation

Force equals pressure multiplied by area. Converting, 100 bar = 10 N/mm² and 20 cm² = 2000 mm², so F = 10 N/mm² × 2000 mm² = 20 000 N = 20 kN. Forgetting the unit conversion of cm² to mm² leads to a factor-of-ten error.

Question 11Technik (fachliche Inhalte des Faches Technik)

Why is a flyback converter able to step a voltage up to a higher level than a simple buck converter?

  1. The output capacitor is charged directly from the input through a diode during the on-time.
  2. It uses a transformer-free topology that doubles the input voltage.
  3. Energy is stored in the inductor during the on-time and transferred to the output during the off-time, allowing the output voltage to exceed the input. Correct answer.
  4. The switching frequency is always higher than in a buck converter.

Explanation

In a flyback topology the inductor (or coupled inductor) stores energy while the switch conducts, and the diode then delivers that energy to the output when the switch opens. This indirect energy transfer permits an output voltage above the input. A buck converter transfers energy directly and therefore only steps down.

Question 12Technik (fachliche Inhalte des Faches Technik)

A stepper motor with a step angle of 1.8° is driven with 400 pulses. Through what angle does the shaft rotate, assuming no lost steps?

  1. 180°
  2. 720° Correct answer.
  3. 1.8°
  4. 400°

Explanation

Each pulse advances the rotor by one step angle, so the total angle is 400 × 1.8° = 720°, which is two full revolutions. This direct multiplication assumes the driver is not using microstepping and no steps are lost.

Question 13Technik (fachliche Inhalte des Faches Technik)

Which statement about a PID controller's integral term is correct?

  1. It amplifies high-frequency noise and therefore destabilises every loop.
  2. It accumulates the error over time and removes steady-state offset. Correct answer.
  3. It reacts only to the rate of change of the error.
  4. It is identical in effect to the proportional term.

Explanation

The integral term sums the error over time, so a small persistent error eventually produces enough corrective action to eliminate the offset. Its strength is set by the integral time. The derivative term, by contrast, responds to the rate of change of the error.

Question 14Technik (fachliche Inhalte des Faches Technik)

A tensile test specimen with an original length of 50 mm stretches to 50.1 mm under load. What is the engineering strain?

  1. 0.002 Correct answer.
  2. 0.02
  3. 0.0002
  4. 0.2

Explanation

Engineering strain is the change in length divided by the original length: (50.1 − 50)/50 = 0.1/50 = 0.002. Strain is dimensionless, often expressed in percent or microstrain. Confusing the absolute extension with the strain gives a wrong value.

Question 15Technik (fachliche Inhalte des Faches Technik)

Which manufacturing process is best suited to producing large numbers of identical plastic housings at low unit cost?

  1. Injection moulding Correct answer.
  2. Hand lay-up of glass fibre
  3. Selective laser sintering
  4. Turning on a lathe

Explanation

Injection moulding forces molten polymer into a steel mould, so the high tooling cost is spread over a large production volume and unit cost falls. It reproduces fine detail and tight tolerances consistently. The other processes are better suited to small batches or to different material classes.

Question 16Technik (fachliche Inhalte des Faches Technik)

In a pneumatic circuit, what is the purpose of a 5/2 directional control valve?

  1. It has five ports and two switching positions and controls a double-acting cylinder. Correct answer.
  2. It converts electrical signals into pneumatic pressure signals.
  3. It filters, regulates and lubricates the compressed air.
  4. It has two ports and five switching positions and regulates pressure.

Explanation

The designation 5/2 states the number of ports (five) and the number of switching positions (two). With two working ports it can drive a double-acting cylinder in both directions and exhaust the opposite chamber. Pressure regulation and air preparation are separate devices.

Question 17Technik (fachliche Inhalte des Faches Technik)

A three-phase induction motor is connected in delta to a 400 V supply. What happens to the phase voltage compared with a star connection on the same supply?

  1. The phase voltage is halved to 200 V.
  2. The phase voltage becomes 690 V.
  3. The phase voltage equals the line voltage of 400 V instead of 230 V. Correct answer.
  4. The phase voltage stays at 230 V in both connections.

Explanation

In a star connection the phase voltage is the line voltage divided by √3, about 230 V for a 400 V supply. In a delta connection each winding is connected directly across two lines, so the phase voltage equals the line voltage of 400 V. This is why star-delta starting reduces the starting current.

Question 18Technik (fachliche Inhalte des Faches Technik)

Which statement best explains why a bridge rectifier with a smoothing capacitor delivers a higher average DC voltage than one without?

  1. The capacitor blocks the DC component and passes only the ripple.
  2. The capacitor reverses the polarity of the output.
  3. The capacitor increases the peak value of the input voltage.
  4. The capacitor stores charge near the peak of the rectified waveform and discharges slowly between peaks, raising the average value. Correct answer.

Explanation

The capacitor charges to nearly the peak of the rectified sine wave and then supplies the load while the input falls, so the output stays near the peak. The average therefore rises towards the peak value and the ripple is reduced. The peak input voltage itself is unchanged.

Question 19Technik (fachliche Inhalte des Faches Technik)

A robot arm has six revolute joints. What does the sixth joint typically provide?

  1. Gripping force at the end effector
  2. Reach along the arm's radial direction
  3. Orientation of the tool about the tool axis Correct answer.
  4. Counterbalance of the arm's own weight

Explanation

In a typical six-axis industrial robot the first three joints position the wrist in space and the last three orient the tool. The sixth joint rotates the tool about its own axis, which is often called the roll. Gripping and counterbalancing are separate functions.

Question 20Technik (fachliche Inhalte des Faches Technik)

A signal of 0–10 V from a pressure sensor is read by a PLC analogue input with a 12-bit resolution over the same range. What is the smallest pressure change the input can resolve, expressed as a fraction of full scale?

  1. About 1/1024 of full scale
  2. About 1/12 of full scale
  3. About 1/256 of full scale
  4. About 1/4096 of full scale Correct answer.

Explanation

A 12-bit converter produces 2^12 = 4096 discrete levels across its range. The smallest resolvable step is therefore one full-scale range divided by 4096. The number of bits, not the voltage range, sets this resolution.

Question 21Technik (fachliche Inhalte des Faches Technik)

A component made of steel is to be joined to a component made of aluminium in a structure exposed to vibration. Which joining method is most appropriate and why?

  1. Riveting with steel rivets, because steel rivets match the aluminium component.
  2. Adhesive bonding with a structural adhesive, because it distributes load and avoids a galvanic couple at the joint. Correct answer.
  3. Gas welding, because both metals melt at similar temperatures.
  4. Soft soldering with a tin-lead solder, because it works on both metals equally well.

Explanation

Adhesive bonding avoids melting dissimilar metals and provides a continuous joint that spreads vibration loads over a large area. It also separates the two metals, reducing galvanic corrosion. Welding dissimilar metals produces brittle intermetallic phases, and steel rivets in aluminium create a corrosion couple.

Question 22Technik (fachliche Inhalte des Faches Technik)

In a closed-loop position control system the proportional gain is increased until the response shows sustained oscillation. What does this indicate?

  1. The sensor has failed and must be replaced.
  2. The loop has reached its stability limit at the critical gain. Correct answer.
  3. The actuator has reached its maximum speed.
  4. The steady-state error has become zero.

Explanation

Sustained oscillation with constant amplitude marks the stability boundary of the loop. The gain at which this occurs is the critical gain, and further increase makes the system unstable. It is a property of the loop dynamics, not evidence of a faulty sensor.

Question 23Technik (fachliche Inhalte des Faches Technik)

A beam of length L is simply supported at both ends and carries a central point load F. How does the maximum bending moment compare with the same beam loaded at one end as a cantilever?

  1. Both cases give the same maximum moment FL/4.
  2. The simply supported central-load case gives FL/4, while the cantilever end-load case gives FL, so the cantilever moment is four times larger. Correct answer.
  3. The cantilever case gives FL/8, which is smaller than the simply supported case.
  4. The simply supported case gives FL/2 and the cantilever gives FL/2.

Explanation

For a simply supported beam with a central load the maximum moment is FL/4 at midspan. For a cantilever with the load at its free end the moment is FL at the support, four times larger for the same load and length. The support conditions therefore strongly affect the required section.

Question 24Technik (fachliche Inhalte des Faches Technik)

Why does a frequency converter with a constant V/f ratio keep the magnetic flux in an induction motor approximately constant when the speed is reduced?

  1. Because the number of pole pairs is changed by the converter.
  2. Because the stator voltage is reduced in proportion to frequency, keeping the ratio of voltage to frequency and thus the flux constant. Correct answer.
  3. Because the converter supplies direct current at low speed.
  4. Because the rotor resistance is increased automatically as the speed falls.

Explanation

Flux is proportional to stator voltage divided by frequency. By lowering the voltage together with the frequency, the converter keeps this ratio constant and avoids magnetic saturation. This also keeps the available torque roughly constant over the speed range.

Question 25Technik (fachliche Inhalte des Faches Technik)

Two resistors of 100 Ω and 150 Ω are connected in parallel across a 12 V source. What current flows from the source?

  1. 0.048 A
  2. 1.2 A
  3. 0.12 A
  4. 0.2 A Correct answer.

Explanation

The equivalent resistance of 100 Ω and 150 Ω in parallel is (100 × 150)/(100 + 150) = 60 Ω. The source current is then 12 V / 60 Ω = 0.2 A, which also equals the sum of the branch currents 0.12 A and 0.08 A.

Question 26Technik (fachliche Inhalte des Faches Technik)

A single-phase transformer is rated 230 V / 24 V. Which statement describes the relationship between the primary and secondary currents in an ideal transformer operating at full load?

  1. The secondary current is larger than the primary current by the turns ratio. Correct answer.
  2. The secondary current equals the primary current because power is conserved.
  3. The primary current is larger than the secondary current by the turns ratio.
  4. Both currents are equal because the core flux links both windings.

Explanation

In an ideal transformer the power in equals the power out, so U1·I1 = U2·I2. Since the secondary voltage is lower by the voltage ratio, the secondary current must be higher by the same ratio. The turns ratio therefore steps current up while it steps voltage down.

Question 27Technik (fachliche Inhalte des Faches Technik)

A DC shunt motor is running at steady speed with a constant mechanical load. If the field current is reduced while the armature voltage stays constant, what happens to the motor speed?

  1. The speed stays constant because the load is unchanged.
  2. The speed increases because the back-EMF must fall to allow more armature current. Correct answer.
  3. The speed decreases because the field is weaker.
  4. The motor stops because the field is required for torque.

Explanation

Speed is proportional to back-EMF divided by flux. Reducing the field flux lowers the back-EMF, so armature current and torque rise, accelerating the motor until the back-EMF again balances the supply at a higher speed. Field weakening therefore raises the speed of a shunt motor.

Question 28Technik (fachliche Inhalte des Faches Technik)

In a measurement chain, a sensor with a high output impedance is connected to an amplifier with a low input impedance. What is the main consequence?

  1. The signal is loaded and the measured voltage drops significantly. Correct answer.
  2. The resolution of the following ADC increases.
  3. The common-mode rejection of the amplifier improves.
  4. The bandwidth of the sensor increases.

Explanation

A voltage divider forms between the source impedance and the input impedance. If the input impedance is low compared with the source impedance, a large part of the signal is lost across the source. Buffer amplifiers with high input impedance are used to prevent this loading effect.

Question 29Technik (fachliche Inhalte des Faches Technik)

A strain gauge with a gauge factor of 2 is bonded to a steel part and experiences a strain of 500 µm/m. What is the fractional change in resistance of the gauge?

  1. 0.001 Correct answer.
  2. 0.1
  3. 0.0001
  4. 0.01

Explanation

The gauge factor is defined as the fractional resistance change divided by strain, so ΔR/R = k·ε. With k = 2 and ε = 500 × 10⁻⁶, the result is 1 × 10⁻³, i.e. 0.001. This small change is why a Wheatstone bridge is normally used to measure it.

Question 30Technik (fachliche Inhalte des Faches Technik)

Which statement correctly describes the difference between a normally open (NO) and a normally closed (NC) contact in an electromechanical relay?

  1. The NC contact is closed when the coil is de-energised. Correct answer.
  2. Both contacts are open when the coil is de-energised.
  3. The NO contact is closed when the coil is de-energised.
  4. The contact state depends only on the load current, not on the coil.

Explanation

The terms describe the rest state, i.e. the state with the coil de-energised. An NC contact conducts in that rest state and opens when the coil is energised, while an NO contact does the opposite. This matters for fail-safe design, where a de-energised circuit should stop the machine.

Question 31Technik (fachliche Inhalte des Faches Technik)

A workpiece on a conveyor is detected by an inductive proximity sensor. Which material change would most reduce the sensor's switching distance?

  1. Mounting the sensor closer to the conveyor frame
  2. Increasing the supply voltage within the rated range
  3. Replacing a steel target with an aluminium target of the same size Correct answer.
  4. Replacing a steel target with a larger steel target

Explanation

Inductive sensors respond to eddy currents in conductive targets, and their rated switching distance is specified for mild steel. Non-ferrous metals such as aluminium have lower permeability and higher resistivity, so the switching distance is reduced, typically by a correction factor.

Question 32Technik (fachliche Inhalte des Faches Technik)

Which logic gate produces a HIGH output only when all of its inputs are HIGH?

  1. AND gate Correct answer.
  2. NAND gate
  3. XOR gate
  4. OR gate

Explanation

The AND function gives a 1 only for the input combination in which every input is 1. In control logic this corresponds to series-connected contacts, which is why AND terms are built from series circuits in ladder diagrams.

Question 33Technik (fachliche Inhalte des Faches Technik)

A ladder diagram uses a normally closed contact of a limit switch in series with a motor contactor coil. What is the effect when the switch is actuated?

  1. The coil is de-energised and the motor stops. Correct answer.
  2. The contactor latches itself on.
  3. The coil state is unchanged because the contact is closed.
  4. The coil is energised and the motor starts.

Explanation

A normally closed contact conducts while the switch is unactuated and opens when it is actuated. Opening the series path interrupts the coil current, so the contactor drops out and the motor stops. This is the standard way to implement an end position or stop function.

Question 34Technik (fachliche Inhalte des Faches Technik)

In a binary-coded decimal (BCD) representation, how many bits are needed to represent one decimal digit?

  1. 3
  2. 8
  3. 10
  4. 4 Correct answer.

Explanation

BCD encodes each decimal digit separately in a 4-bit group, using the binary patterns for 0 to 9. The remaining six patterns of the 4-bit group are unused. Four bits are the minimum because three bits provide only eight combinations.

Question 35Technik (fachliche Inhalte des Faches Technik)

A 4-bit successive-approximation ADC has a reference voltage of 8 V. What is its resolution?

  1. 0.25 V
  2. 0.5 V Correct answer.
  3. 1.0 V
  4. 2.0 V

Explanation

The resolution equals the reference voltage divided by the number of steps, 2⁴ = 16. Thus 8 V / 16 = 0.5 V per least significant bit. The number of quantisation levels, not the number of bits, sets the step size.

Question 36Technik (fachliche Inhalte des Faches Technik)

Which statement describes the purpose of a Wheatstone bridge in a measurement circuit?

  1. It converts an analogue voltage into a digital code.
  2. It produces a zero output when the bridge is balanced, so small resistance changes can be measured precisely. Correct answer.
  3. It amplifies a small differential signal.
  4. It supplies a constant current to the sensor regardless of load.

Explanation

A Wheatstone bridge compares four resistances and gives zero differential voltage at balance. A small change in one arm then produces an output proportional to that change, which can be amplified and read accurately. This null method reduces the effect of supply drift.

Question 37Technik (fachliche Inhalte des Faches Technik)

An operational amplifier is used as a non-inverting amplifier with R1 = 10 kΩ and Rf = 40 kΩ. What is the voltage gain?

  1. 0.2
  2. 5 Correct answer.
  3. −4
  4. 4

Explanation

For the non-inverting configuration the gain is 1 + Rf/R1. Substituting the values gives 1 + 40/10 = 5. The positive sign confirms that the output is in phase with the input.

Question 38Technik (fachliche Inhalte des Faches Technik)

Why is a diode often connected in parallel with the coil of a relay that is switched by a transistor?

  1. To reduce the contact bounce of the relay.
  2. To rectify the supply voltage for the coil.
  3. To provide a path for the induced voltage when the coil is de-energised. Correct answer.
  4. To increase the coil current during switching.

Explanation

An inductive coil stores magnetic energy, and interrupting the current produces a large voltage spike that can destroy the transistor. A freewheeling diode gives the coil current a path to decay safely. The diode is connected in reverse bias during normal operation.

Question 39Technik (fachliche Inhalte des Faches Technik)

In a hydraulic system, a pressure relief valve is set to 120 bar and the pump delivers 20 L/min against a load that requires only 5 L/min. What happens to the excess flow?

  1. It is blocked by the pump and the pump stops.
  2. It is stored in the accumulator.
  3. It increases the speed of the actuator.
  4. It returns to the tank through the relief valve at 120 bar. Correct answer.

Explanation

A fixed-displacement pump delivers a nearly constant flow. When the load consumes less, the pressure rises until the relief valve opens and bypasses the excess flow back to the tank at the set pressure. The energy in that bypassed flow is dissipated as heat.

Question 40Technik (fachliche Inhalte des Faches Technik)

Which property mainly distinguishes a thermosetting plastic from a thermoplastic during processing?

  1. Thermosets can be remelted repeatedly, thermoplastics cannot.
  2. Thermosets are only used for electrical insulation.
  3. Thermoplastics are always reinforced with glass fibres.
  4. Thermosets cure irreversibly by cross-linking, while thermoplastics soften reversibly on heating. Correct answer.

Explanation

In thermosets, chemical cross-links form during curing and cannot be undone by heating, so the material degrades rather than melting. Thermoplastics consist of linear or branched chains that soften on heating and harden on cooling without a chemical change. This is why thermoplastics are easier to recycle by melting.

Question 41Technik (fachliche Inhalte des Faches Technik)

During a hardness test using the Brinell method, a hardened steel ball is pressed into a specimen. Which change would increase the measured Brinell hardness number for the same material?

  1. A smaller diameter of the resulting indentation at the same force Correct answer.
  2. A larger applied test force with the same ball
  3. A longer dwell time beyond the standard period
  4. A softer ball material

Explanation

The Brinell hardness number is proportional to the applied load divided by the curved surface area of the indentation. A smaller indentation at the same force therefore means a higher hardness number. The ball diameter and load must be chosen according to the standard so that results remain comparable.

Question 42Technik (fachliche Inhalte des Faches Technik)

Which statement about the fatigue strength of a steel component is correct?

  1. Fatigue strength is independent of surface finish.
  2. Fatigue failure occurs only above the yield strength of the material.
  3. Repeated stress cycles below the tensile strength can cause failure after many cycles. Correct answer.
  4. Fatigue cracks always start in the component's core.

Explanation

Fatigue is progressive damage under cyclic loading, and failure can occur at stress amplitudes well below the tensile strength, often below the yield strength. Cracks usually initiate at stress concentrations on the surface. This is why surface quality and notch geometry strongly influence fatigue life.

Question 43Technik (fachliche Inhalte des Faches Technik)

A shaft transmits torque through a keyed joint. Which change most directly increases the shear stress in the key?

  1. Increasing the key material's yield strength
  2. Increasing the shaft diameter while keeping the torque constant
  3. Reducing the length of the key while keeping the torque constant Correct answer.
  4. Increasing the key width while keeping the torque constant

Explanation

The key carries the torque as a shear force distributed over its shear area, which is the product of key length and width. Shortening the key reduces that area, so for the same torque the shear stress rises. A longer key or a wider key reduces the stress.

Question 44Technik (fachliche Inhalte des Faches Technik)

A cantilever beam of length L carries a point load F at its free end. At which point does the maximum bending stress occur?

  1. It is uniform along the beam
  2. At the free end
  3. At mid-span
  4. At the fixed support Correct answer.

Explanation

The bending moment of an end-loaded cantilever is F·x measured from the free end, so it is largest at the fixed support. Bending stress is proportional to the bending moment, so the maximum stress also occurs at the support. The free end carries no moment at all.

Question 45Technik (fachliche Inhalte des Faches Technik)

Which statement describes the function of a bearings' preload in a machine tool spindle?

  1. It removes internal clearance and increases stiffness at the cost of higher friction. Correct answer.
  2. It increases the internal clearance to reduce friction.
  3. It compensates for thermal expansion by loosening the bearing fit.
  4. It reduces the bearing's load-carrying capacity.

Explanation

Preload applies an axial or radial force that eliminates internal clearance between rolling elements and raceways. This raises the stiffness of the spindle and improves running accuracy, but friction and heat generation increase. Excessive preload shortens bearing life.

Question 46Technik (fachliche Inhalte des Faches Technik)

In a CNC machine, which coordinate system is defined relative to the workpiece and is normally set by the operator during setup?

  1. Tool coordinate system
  2. Machine coordinate system
  3. Machine reference system
  4. Workpiece coordinate system Correct answer.

Explanation

The workpiece coordinate system is established by the operator, for example by touching on the workpiece with a tool, and its origin is the programmed zero point. The machine coordinate system is fixed by the machine's reference points and is independent of the part. Programs are normally written in workpiece coordinates.

Question 47Technik (fachliche Inhalte des Faches Technik)

A robot is programmed to move its tool centre point along a straight line between two points while maintaining a specified orientation. Which interpolation mode is required?

  1. Circular interpolation
  2. Point-to-point interpolation without path control
  3. Joint interpolation
  4. Linear interpolation Correct answer.

Explanation

Linear interpolation (often called MOVL) keeps the tool centre point on a straight line between the start and end points and controls the orientation along the path. Joint interpolation moves each axis independently, so the tool path is not a straight line. Circular interpolation produces an arc rather than a line.

Question 48Technik (fachliche Inhalte des Faches Technik)

Which statement about a three-phase squirrel-cage induction motor running at no load is correct?

  1. The slip is close to 0 and the rotor frequency is very low. Correct answer.
  2. The slip is close to 1 and the rotor frequency is high.
  3. The slip is negative and the machine acts as a generator.
  4. The slip is exactly 1 because the rotor is stationary.

Explanation

Slip is defined as (ns − n)/ns. At no load the rotor speed is only slightly below synchronous speed, so slip is small, typically a few percent or less. The rotor frequency equals slip times the stator frequency and is therefore also very low.

Question 49Technik (fachliche Inhalte des Faches Technik)

A DC motor is controlled by pulse-width modulation with a supply voltage of 24 V. What average voltage is applied if the duty cycle is 25 %?

  1. 24 V
  2. 18 V
  3. 12 V
  4. 6 V Correct answer.

Explanation

The average voltage of a PWM waveform equals the duty cycle multiplied by the supply voltage. With a duty cycle of 0.25 and 24 V, the average is 6 V. The switching frequency is chosen high enough that the motor current is smoothed by its inductance.

Question 50Technik (fachliche Inhalte des Faches Technik)

Why is a boost converter unable to operate correctly if the switch is held permanently closed?

  1. The diode conducts continuously and the output equals the input.
  2. The output voltage rises without limit.
  3. The capacitor discharges through the switch.
  4. The inductor is bypassed and the output falls to zero while the diode is reverse biased. Correct answer.

Explanation

In a boost converter the inductor is charged while the switch is on and delivers energy to the output through the diode while the switch is off. If the switch stays closed, the inductor is connected directly across the input and the diode is reverse biased, so no energy reaches the output. The output voltage therefore collapses under load.