First, multiple choice questions
1. In DC circuits, the correct expression for Kirchhoff's second law is (B).
(A) ∑ =0 (B) ∑∪ = 0 (C) ∑IR=0 (D) ∑E=0
2. In the common emission stage amplifying circuit, when the load resistance increases, the value of the voltage amplification factor will be (C).
(A) constant (B) decrease (C) increase (D) decrease rapidly
3. Divide 3 magnets into 6 blocks from the middle to obtain (D) magnetic poles.
(A) 6 (B) 8 (C) 10 (D) 12
4. The following materials are used to form four magnetic circuits of the same specification, and the material with the largest magnetic resistance is (C).
(A) Iron (B) Nickel (C) Brass (D) Cobalt
5. In the magnetic circuit composed of ferromagnetic materials, the reason why the reluctance is nonlinear is that (A) is nonlinear.
(A) Magnetic permeability (B) Magnetic flux (C) Current (D) Magnetic field strength
6. The scan generator in an oscilloscope is actually an (A) oscillator.
(A) sine wave (B) multi-harmonic (C) capacitor three-point (D) inductor three-point
7. The size of the coil's self-induced electromotive force is independent of (D).
(A) Rate of change of current in the coil (B) Number of turns of the coil
(C) Medium around the coil (D) Resistance of the coil
8. The polarity of the transformer coil is generally determined according to (D).
(A) Right-hand rule (B) Left-hand rule (C) Lenz's law (D)
9. When observing the input characteristics of the common emitter amplifier circuit with a transistor plotter, (D).
(A) The X-axis action switch is placed at the base voltage, and the Y-axis action switch is placed at the collector current.
(B) The X-axis action switch is placed at the collector voltage, and the Y-axis action switch is placed at the collector current.
(C) The X-axis action switch is placed at the collector voltage, and the Y-axis action switch is placed at the base voltage
(D) The X-axis action switch is placed at the base voltage, and the Y-axis action switch is placed at the base current.
10. The synchronous oscilloscope adopts the trigger scanning mode, that is, the external signal is triggered once, and (A) scanning voltage waveform is generated.
(A) 1 (B) 2 (C) 3 (D) 4
11. The commutating pole polarity of the DC motor and the next main pole polarity (B) that is diverted along the armature.
(A) Same (B) Reverse (C) Series (D) Parallel
12. The electronic switch in the SR-8 dual-track oscilloscope has (D) operating states.
(A) 2 (B) 3 (C) 4 (D) 5
13. When actually adjusting the static operating point of the analog amplifier circuit, it is generally based on (A).
(A) Ib (B) Ic (C) Uce (D) Ube
14. In DC amplifiers, the main cause of zero drift is the change in (D).
(A) Frequency (B) Collector current (C) Transistor (D) Temperature
15. In the arithmetic circuit, the integrated operational amplifier operates in a linear region, so (B) is introduced, and various mathematical operations are implemented using a feedback network.
(A) Deep positive feedback (B) Deep negative feedback
(C) shallow positive feedback (D) shallow negative feedback
16. When both TTL and NAND input are floating at the same time, the output is (B).
(A) Zero level (B) Low level
(C) High level (D) may be low level or high level
17. Among the following digital displays, the most power-saving is (A).
(A) Liquid crystal display (B) Fluorescent digital tube
(C) LED display (D) Glow digital tube
18. The disadvantage of power transistors is (D).
(A) Small power capacity (B) must have a dedicated forced commutation circuit
(C) has linear amplification characteristics (D) susceptible to damage due to secondary breakdown
19. The input and output circuits of the electronic equipment should not be as close as possible to avoid (C).
(A) Short circuit (B) Breakdown (C) Self-oscillation (D) Personal accident
20. Large transformers often use (C) sections to make full use of space.
(A) Square (B) Rectangular (C) Stepped (D) Round
21. When cleaning inside the transformer, the sludge in the fuel tank and iron core can be scraped off with a blade, cleaned with a cloth, and then rinsed with transformer oil. Never use (D) to brush.
(A) Engine oil (B) Strong oil (C) Kerosene (D) Alkaline water
22. The stator structure of a hydro-generator is basically the same as that of a three-phase asynchronous motor, but the rotor is generally of the type (A).
(A) salient pole (B) shade pole (C) hidden pole (D) claw pole
23. For the winding and weaving of the rotor windings of three-phase asynchronous motors, the larger capacity of the wound rotor windings is adopted (B).
(A) Flat aluminum wire (B) Bare copper strip (C) Aluminum wire (D) Round copper wire
24. Faults in three-phase asynchronous motors can generally be classified into categories (A).
(A) 2 (B) 3 (C) 4 (D) 5
25. According to the technical requirements, (B) the motor is subjected to an overspeed test.
(A) squirrel-cage asynchronous (B) wire-wound asynchronous
(C) DC (D) synchronization
26. For transformer withstand voltage test, the voltage duration is (A) minutes.
(A) 1 (B) 2 (C) 3 (D) 5
27. When the three-phase asynchronous motor starts, the starting current is large and the starting torque (D).
(A) Maximum (B) Large (C) Zero (D) Not very large
28. The DC motor uses energy-consuming braking, which is the (C) magnetic flux generated by the excitation current, which in turn generates an induced electromotive force, causing the motor to brake.
(A) alternating (B) sine (C) constant (D) pulsating
29. Wire-wound asynchronous motor, when the series resistance of the rotor is used for speed regulation, the greater the resistance in series, the speed (C).
(A) does not change with resistance (B)
(C) The lower (D) the speed can be determined
30. The tachogenerator has two sets of windings whose output windings are connected to (C).
(A) Voltage signal (B) Short-circuit wire (C) High-impedance meter (D) Low-impedance meter
31. The rotor of an AC servo motor is usually of the type (D).
(A) hood pole (B) salient pole (C) wirewound (D) squirrel cage
32. The basic working principle of the generator is (A).
(A) Electromagnetic induction (B) Magnetic effect of current
(C) Thermal effect of current (D) Conductive conductor is stressed in a magnetic field
33. When a linear asynchronous motor adopts the rotor string resistance speed regulation, a large amount of energy will be consumed in the resistance, and the relationship between the speed adjustment and the loss is (B).
(A) The higher the speed, the greater the loss (B) The lower the speed, the greater the loss
(C) The lower the speed, the smaller the loss (D) The speed of the speed is independent of the loss
34. According to the special case of the brushless motor, the speed control method for changing the armature voltage is (D).
(A) Generator control voltage controlled by motor amplifier
(B) Adjusting the armature voltage supplied to the DC motor with a separately excited DC generator
(C) Weak magnetic speed regulation
(D) With the electronic commutation switch circuit, the on-time of each phase remains unchanged, and the magnitude of the voltage applied to the coil when each phase is turned on is used to achieve the speed regulation.
35. (B) The speed of the AC asynchronous motor cannot be changed.
(A) Changing the number of pole pairs of the stator winding (B) Changing the voltage of the power supply grid
(C) Change the frequency of the power supply grid (D) Change the slip of the motor
36. When the speed range of the rotor-powered three-phase shunt AC commutator motor is within (B), the speed regulation is very high.
(A) 1:1 (B) 3:1 (C) 5:1 (D) 10:1
37. The variable frequency power supply in variable frequency speed regulation is the interface between (C).
(A) Mains power supply (B) AC motor
(C) Mains power supply and AC motor (D) Mains power supply and AC power supply
38. In the method of DC motor speed regulation, (C) can realize stepless speed regulation and low energy loss.
(A) DC-excited generator jujube DC motor unit (B) Change armature loop resistance
(C) Chopper (D) weakens the magnetic field
39. The voltage negative feedback speed control system achieves the purpose of stabilizing the speed by stabilizing the armature voltage of the DC motor. The principle is the change of the armature voltage and (A).
(A) The change in speed is proportional to (B) the change in speed is inversely proportional
(C) The square of the change in rotational speed is proportional to (D) The inverse of the square of the change in rotational speed
40. The cut-off method of current cut-off negative feedback can be realized not only by (B) comparison method, but also by connecting a Zener tube in the feedback loop.
(A) Current (B) Voltage (C) Power (D) Charge
41. Speed ​​control system with double closed loop of speed and current, the adjustment function is mainly generated by (A) regulator at startup.
(A) Current (B) Speed ​​(C) Negative feedback voltage (D) Current, speed two
42. The main parameters of the magnetic tape are dynamic range, accuracy, and resolution, where the dynamic range should be (C).
(A) 1 to 40 m (B) 1 to 10 m (C) 1 to 20 m (D) 1 to 50 m
43. The CNC system works when it is (C).
(A) First interpolation, post processing (B) First processing, then interpolation
(C) Processing while processing (D)
44. The numerical control system of modern CNC machine tools is composed of machine control program, numerical control device, programmable controller, spindle control system and feed control system. The core part is (C).
(A) Feed control system (B) Programmable controller
(C) Numerical control device (D) Spindle control system
45. The operating speed of an AC two-speed elevator should generally be less than (A)m/s.
(A) 1 (B) 2 (C) 2.5 (D) 3
46. ​​Measures to reduce the basic time are (A).
(A) Using new technologies, new equipment, and new processes (B) to shorten the auxiliary time
(C) Reduce preparation time (D) Reduce rest time
47. Exchange collection elevator, when the elevator (free state) runs from the 3rd floor, the 2nd floor is pressed by the up call button, the 4th floor is pressed by the downward call button, the 5th floor is pressed by the up call button and the car is at the same time. Someone presses the button on the 1st floor and the elevator should stop at the (A) floor.
(A) 5 (B) 4 (C) 2 (D) 1
48. plc AC two-speed elevator, PLC output interface generally adopts (B) mode.
(A) Thyristor (B) Relay (C) Transistor (D) Single Crystal Tube
49. When the rated speed of the PLC AC elevator is greater than 0.63m/s, the safety gear should be selected (A).
(A) Progressive (B) Parabola (C) Instantaneous (D) Ellipse
50. Regarding the characteristics of computers, (D) is a wrong statement.
(A) High computing speed (B) Memory and logic judgment
(C) High precision of operation (D) Operation process cannot be automatic and continuous, requiring manual intervention
51. A complete computer hardware system includes (A).
(A) Computer and its peripherals (B) Main unit, keyboard and display
(C) Digital Circuit (D) Integrated Circuit
52. The main reason for using binary in computers is (D).
(A) Fast calculation speed (B) High precision operation
(C) Simple algorithm (D) Electronic component characteristics
53. Single-phase half-bridge inverters (voltage type) have (B) conductive arms.
(A) 1 (B) 2 (C) 3 (D) 4
54. Working hours quotas usually include working hours, time spent on work placement, time required for rest and living, and (A) and end time.
(A) Processing preparation
(B) Auxiliary time
(C) Loss of downtime
(D) Time spent on non-productive work
55. Measures to reduce the basic time are (A).
(A) Increase the auxiliary time with new equipment (B)
(C) Reduced preparation time (D) Reduced layout work time
56. Measures to shorten the auxiliary time are (A) time.
(A) Properly compile the operating process and reduce unnecessary assistance
(B) Shorten the work (C) Reduce the rest
(D) Reduce preparation
57. PLC exchange two-speed elevator, the current floor indicator is generally adopted (A).
(A) Seven-segment digital tube (B) signal light (C) pointer (D) LED
58. The function of the flanges at both ends of the split bearing bush is (D).
(A) Increase the stiffness of the bearing bush (B) Easy to manufacture
(C) Easy maintenance (D) Prevent axial movement of the bearing bush
59. Couplings that compensate for poor or skewed alignment of two shafts are (B) couplings.
(A) Flange (B) Slider (C) Sleeve (D) Gear
60. The distance between the suction pipe and the return pipe of the open fuel tank should be (B).
(A) Nearest point (B) As far as possible (C) Two together (D) The closer the better, the judgment question
(√ ) 61. When using an oscilloscope, do not open or close the power supply frequently to prevent damage to the filament of the oscilloscope tube.
(X)62. The most effective measure to overcome zero drift is to use an AC negative feedback circuit.
(X)63. In the case where an external input signal is not required, the phenomenon that the amplifying circuit can output a continuous DC signal having a sufficient amplitude is called oscillation. 6
(X)64. The output voltage of the series regulator circuit can be arbitrary.
(√) 65. The logic function of the NOT gate can be summarized as 0 out of 1, with 1 out of 0.
(√) 66. The frequency stability of the quartz crystal multivibrator is higher than that of the TTL and non-gate RC ring multivibrator.
(X)67. The role of the thyristor chopper is to change the adjustable DC voltage to a fixed DC voltage.
(X)68. Power FETs are ideal current control devices.
(X)69. The commutating pole core of a general DC motor is stacked with silicon steel sheets.
(X)70. The DC generator generates an AC electromotive force under the drag of the prime mover, and then generates a DC voltage output through the armature.
(√) 71. A resolver is a signal component whose output voltage varies with the rotor angle.
(X)72. The self-aligning machines used in the automatic and remote control systems are single motors.
(X)73. DC torque motors are generally constructed as electromagnetic low-frequency magnetic fields.
(√) 74. The three-phase AC commutator motor has a proportional increase or decrease in output power and motor speed because the motor has constant torque characteristics.
(√) 75. The chopper is a DC/DC converter.
(√) 76. The speed regulation range satisfies a certain static rate condition. Similarly, the static difference rate is said to meet a certain speed regulation range.
(X)77. The dynamic characteristics of the speed negative feedback speed control system depend on the closed loop magnification of the system.
(√) 78. The physical quantity reflected by the positive feedback of the current is the magnitude of the motor load, not the magnitude of the adjusted voltage or speed.
(X)79. In a voltage-type inverter, a large inductor is used to buffer the non-functional amount.
(X)80. The calculated diameter of the V-belt pulley is the outer diameter of the pulley.
Third, short answer questions
81. What are the requirements for the collector scan voltage in the transistor plotter?
A: There are three requirements for the collector scan voltage:
1 can be repeated from small to large, and then from large to small (1 point) repeat continuous change (1 point).
2 The repetition frequency of the scan should be fast enough (1 point) to avoid the displayed curve flickering (1 point).
3 The maximum value of the scan voltage should be adjusted within a few hundred volts according to the requirements of different transistors (1 point).
82. In a normal oscilloscope, what is the difference between a trigger scan and a general scan?
A. The general scan is a sawtooth generator that self-excited to produce a linearly varying sawtooth wave (1 point) without external signal control.
The trigger scan cannot self-excite a sawtooth wave that changes linearly. It must be triggered by an external signal to generate a sawtooth wave (1 point).
The external signal is triggered once, it generates a sawtooth sweep voltage, and the external signal is continuously triggered, which can generate a series of scan voltages (1 point).
Using the trigger scan can not only observe the periodic occurrence of the pulse (1 point), but also observe the non-periodic pulse, and even observe the single-shot pulse (1 point).
Fourth, the calculation questions
83. There is a three-phase half-controlled bridge rectifier circuit connected to a three-phase transformer with a secondary voltage of 200V, and the adjustment range of the average value of the output voltage is obtained.
Answer: ∵ULAV=2.34U2COSα (1 point)
When α=0, ULAV = 2.34 × 200COS0 ° = 468V (2 points)
When α=90, ULAV = 2.34 × 200COS90° = 0V (1 point)
∴The output voltage average adjustment range is between 0V and 468V (1 point)
84. There is a model of Y112M-2 asynchronous motor whose technical data is: rated power PN=4KW, rated speed nN=2890r/m, rated voltage UN=380V, rated current IN=8.2A, efficiency η=85.5%, The power factor cos φ = 0.87.
Seeking: 1 What is the rated torque TN of the motor?
2 How many kilowatts is the input power of the motor?
Answer: 1 The rated torque of the motor TN=9550(PN/nN)=9550(4/2890)=13.2(牛米) (3)
2 motor input power P1=4/η=4/0.855=4.68 (kW) (2)
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