Тест для электромехаников (CES v5.0)

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Правильные ответы:
1

Which of the following is the minimum acceptable value of insulation resistance for High Voltage equipment?

Ваш ответ правильный:

1 M Ohms.
2

High Voltage systems rely on the installed protective equipment being able to interrupt any fault in the system. Throughout the system, the fault level has been calculated, and under no circumstances must the system be modified to exceed this fault level. What is meant by fault level?

Правильный ответ:

The amount of apparent power that could flow into any fault at any point in the electrical network.

Ваш ответ:

The current level flowing into a dead short to earth at any point on the ship, directly from the High Voltage system.
3

When there is a need to interrupt current flow in a High Voltage system it may be very difficult to quench the electrical arc, which is generated at the circuit breaker contacts. Which of the following among media is commonly found in High Voltage marine switchgear?

Правильный ответ:

Vacuum.

Ваш ответ:

Air.
4

A High Breaking Capacity fuse found in a Main High Voltage Switchboard will typically have fault level rating of:

Ваш ответ правильный:

40 kA.
5

“Protective discrimination” means the progressive grading of sizes, or tripping times of:

Ваш ответ правильный:

Line fuses and overcurrent relays.
6

This is a typical emitter follower. What is the main reason for use of an emitter follower?

Правильный ответ:

The input impedance is made much larger than the output impedance.

Ваш ответ:

The V out is always equivalent to the V in.
7

The amplifier circuit is a common configuration used to amplify the difference in voltage between two input signals. In this case input 1 and 2. What is amplifier called?

Ваш ответ правильный:

Differential amplifier.
8

Which of the function shown is this operational amplifier circuit performing?

Ваш ответ правильный:

Integrator.
9

Which function is this operational amplifier circuit performing?

Ваш ответ правильный:

Differentiator.
10

The figure shows a silicon controlled rectifier with a RC circuit connected in parallel. What is the purpose of the RC circuit?

Правильный ответ:

Protect the SCR against damage caused by fast high voltage spikes.

Ваш ответ:

Provide a controlled time delay for the SCR trigger pulse.
11

This is a parallel L-C circuit with a curve showing frequency – impedance characteristics. Which of the formula gives the resonant frequency fo?

Ваш ответ правильный:

fo = 1/(2*Pi*sqrt(L/C)).
12

Ordinary thyristors (SCR) must often be protected against reverse overvoltage transients, because even over-voltages of extremely short duration can destroy them. These SCRs have been given such over-voltage protection, but only one of them is correct. Which?

Ваш ответ правильный:

Figure 1.
13

These circuits are all active filters. Which of the circuits is a low-pass filter?

Правильный ответ:

Figure B.

Ваш ответ:

Figure A.
14

Diodes are widely used in rectification, or the convension of alternating current to direct current. The sinusoidal input voltage V (in) is applied to the circuit shown. Which of the output voltages is correct?

Ваш ответ правильный:

Figure 1.
15

The circuit symbol is a driver for a solenoid (coil) of a solenoid valve S. What is purpose of the diode IN 4 002 connected in parallel to the solenoid S?

Ваш ответ правильный:

Allowing stored energy in solenoid to dissipate as freewheel current, and therefore prevent damage to transistor from inductive switching voltage.
16

The diode shown performs which function?

Правильный ответ:

Return inductive current to supply at switch off.

Ваш ответ:

Provide an overload route for transistor current.
17

The circuit shown is a logic gate with two “high” input signals, A and B, and one output signal Q. Which type of logic function does the gate provide?

Ваш ответ правильный:

OR gate.
18

The wheatstone resistance bridge is often used for measuring resistances in, for example, Pt 100 temperature sensors or strain gauges. This figure shows such a bridge. Under what conditions will the bridge be balanced? I.e. the current through the meter i(m) = 0.

Правильный ответ:

R1/R2 = R3/R4.

Ваш ответ:

R1+R3 = R2+R4.
19

What function is this circuit performing?

Ваш ответ правильный:

Differentiating.
20

This graphical symbol is a logic gate. Which type of gate?

Ваш ответ правильный:

AND.
21

An important quantity which is useful in circuit analysis is known as conductance G (Siemens). Which of the formulas express the conductance for this circuit?

Ваш ответ правильный:

G = 1/R.
22

A 5 V DC source has an internal impedance of 0,2 ohms. When a load of 2,3 ohms is applied what voltage will be measured at the source terminals?

Правильный ответ:

4,6 V.

Ваш ответ:

4,8 V.
23

What principle of measurement are viscosity controllers usually based upon?

Ваш ответ правильный:

Measurement of differential pressure.
24

What is the maximum current that a 15 V, 3 Watt Zener diode can handle without damage?

Ваш ответ правильный:

0,2 A.
25

The inductance, which will induce an EMF of 1 Volt in a conductor, when the current is changing at a rate of 1 Amp per second, is defined as:

Ваш ответ правильный:

One Henry.
26

The typical current gain for a common emitter transistor is:

Ваш ответ правильный:

10-200.
27

The instrument most widely used for testing of semiconductor diodes is:

Ваш ответ правильный:

Multi-meter.
28

A 6-Volt DC relay is to be used with a 12-Volt power supply. The relay requires a current of 0,1 Amp. What is the series resistance required?

Ваш ответ правильный:

60 Ohm.
29

Some ships generate electrical power at 440 V, but then step up this voltage to supply specific electrical equipment. One common example, may be to feed a large bow thruster. Why is this done?

Правильный ответ:

A large bow thruster will draw very large currents at low voltage. Being typically remote from the generator, significant voltage drops would occur at low voltage.

Ваш ответ:

The overall ship’s electrical load does not justify High Voltage generating plant. This method allows more power to be delivered to the bow thruster at low running cost.
30

When work must be done on High Voltage equipment, it is vital that the equipment is earthed (grounded) after isolation procedures have been carried out. Why is this?

Ваш ответ правильный:

To ensure that no energy remains in the system, and that it cannot be recharged by external influences.
31

When selecting switchgear to work with High Voltage it is important to use an appropriate arcing medium. What is meant by arcing medium?

Ваш ответ правильный:

The gas, liquid or vapour, which will minimise creation of an electric arc as contacts open.
32

Sometimes an early warning of failure in High Voltage switchboards may be an unpleasant smell. If the switchboard uses gas circuit breakers, which of the following may indicate a potential problem?

Правильный ответ:

Rotten eggs.

Ваш ответ:

Chlorine.
33

A ship’s electrical system operates at 60 Hz, but when connected to shore supply it is supplied with 50 Hz. Which of the following would you expect?

Ваш ответ правильный:

Electric motors will run at reduced speed, and will tend to overheat.
34

When starting three phase induction motors there is sometimes a need to use a star-delta starter. A star-delta starter exhibits, which of the following characteristics while connected in star.

Ваш ответ правильный:

Reduced current and reduced torque.
35

A 3-phase cage rotor induction motor requires protection by a time delay overload trip. What is the reason for this?

Ваш ответ правильный:

It will allow for inrush current, or motor specific faults.
36

A cable has a resistance of 100 milli-ohms. It supplies a 300 A load over a distance of 100 metres. What is the voltage drop along it’s length?

Ваш ответ правильный:

30 volts.
37

Low voltage ships tend to have insulated neutral systems. What is the reason for this?

Правильный ответ:

In the event of an earth fault vital equipment will not trip.

Ваш ответ:

If the neutral is not insulated, then it may short to other conductors.
38

Power is available at a three-phase motor starter, but nothing happens (at starter or motor) when the start button is operated. Which of the following is a likely cause?

Ваш ответ правильный:

Faulty contactor coil.
39

The continuity resistance of a 100 m long x 25 sq. mm cable (rated at 100 A) is to be checked. Which of the following results would you anticipate?

Ваш ответ правильный:

Between 0,1 and 1,0 Ohm.
40

When performing electrical testing of a three phase motor, insulation resistance measurements may be influenced by which of the following?

Ваш ответ правильный:

Temperature, pressure and dampness.
41

A transformer overheats while taking a shore supply. Which is the likely cause?

Правильный ответ:

Incorrect frequency

Ваш ответ:

Incorrect current.
42

Continuity testing of a delta connected three phase induction motor yields the following results; U1-V1 = 4 Ohms, V1-W1 = 4 Ohms, W1-U1 = 4 Ohms. What is the value of continuity resistance for each winding i. e. U1-U2?

Правильный ответ:

6 Ohms.

Ваш ответ:

4 Ohms.
43

When considering instrumentation systems, what is typical symptom of a fault with the span of an instrument?

Правильный ответ:

Zero-point is accurate, but 100 % input is not giving 100 % output.

Ваш ответ:

100 % output is accurate, but Zero-point is wrong.
44

Continuity testing of a delta connected three phase induction motor yields the following results: U-V = 3 Ohms, V-W = 3 Ohms, W-U = 6 Ohms. Which of the following is the likely condition?

Правильный ответ:

Open circuit winding between W and U.

Ваш ответ:

Partial fault between W and U.
45

A 250 V contactor has been fitted to a 220 V supply. Which of the following symptoms might be observed?

Ваш ответ правильный:

Contactor chattering (vibrating).
46

Routine maintenance insulation testing of a three-phase inductuion motor should cover which measurements?

Ваш ответ правильный:

U-E, V-E, W-E, U-V, V-W, W-U.
47

When measuring level of liquids with a conductivity level indicator, measurement is performed by:

Правильный ответ:

Electrodes.

Ваш ответ:

Capacitance probe.
48

When considering instrumentation systems, what is the meaning of the expression “dead-band”?

Правильный ответ:

The controller will not react to a process change in this range.

Ваш ответ:

The controller will not respond to adjustment of set-point.
49

What should be the healthy continuity resistance of a 220 V, 2,2 kW, 10 A heating element, when checked near to it’s rated operating temperature?

Ваш ответ правильный:

22 Ohms.
50

A thermistor, which provides feedback for a thermal control system, is suspected to have failed. Assuming there is no available replacement, which of the following methods may be used to prove it has failed?

Правильный ответ:

Disconnect the thermocouple lead from the controller, and replace with a mV source.

Ваш ответ:

Disconnect the thermocouple lead from the controller, and replace with a mA source.
51

A triac is used to provide temperature control of an oven. The galley complain that the oven only reaches approximately 50 % of demanded temperature. Which of the following is a likely cause?

Ваш ответ правильный:

One of the main switching elements in the triac has failed.
52

The coil of a 12 V, 120 mA DC relay must be connected across a 24 V supply. What action should be taken?

Ваш ответ правильный:

Install a 100 Ohm resistor in series with the coil.
53

A galley hot plate uses a Nichrome/Magnesium Oxinde heating element, and is to be tested before being put into service for the first time. An insulation resistance test yields a reading of 0,3 M Ohm. Which action should be taken?

Правильный ответ:

Apply reduced voltage to the element for a few minutes. Then retest, and if ok put into service.

Ваш ответ:

Discard the element.
54

What kind of electrolyte is used for Nickel-iron batteries?

Ваш ответ правильный:

Solution of potassium hydroxide (KOH) and water.
55

Two reference points for pressure exist, absolute zero and atmospheric pressure. What are pressures measured relative to absolute zero called:

Ваш ответ правильный:

Absolute pressure.
56

A transformer is rated at 22 kVA, 440/220 Volts, 60 Hz, is used to step down the voltage to a lighting system. The low tension voltage is to be kept constant at 220 Volts. What load impedance connected to the low-tension side will cause the transformer to be fully loaded?

Ваш ответ правильный:

2,2 Ohms.
57

In the circuit diagram shown the starter connects between which terminals?

Ваш ответ правильный:

5 and 6.
58

What is the advantage of a transmitter with a narrow measurement range?

Ваш ответ правильный:

Better linearity and increased accuracy.
59

Some automated control systems use a master controller and a slave controller. What is the meaning of “remote mode” related to a slave controller?

Правильный ответ:

The slave controller receives the set-point from the output signal of the master controller.

Ваш ответ:

The slave controller can be turned by a hand carried remote controller.
60

When turning a cascade control system, which of the following actions should be done first?

Правильный ответ:

Adjust the slave controller with the master controller in manual mode.

Ваш ответ:

Adjust the master controller with the slave controller disabled
61

In the context of an automated process control system, what is understood by the expression Master Controller?

Ваш ответ правильный:

The primary controller in a cascade control system.
62

In which of the following automated control processes will the time constant be of minor importance?

Правильный ответ:

Level control.

Ваш ответ:

Flow control.
63

In terms of automated control systems, what is typical for a continuous control system?

Ваш ответ правильный:

It is possible to predict the control mathematically.
64

Which of the following is typical for a feed-forward control system?

Правильный ответ:

Control of the process inlet side.

Ваш ответ:

Easy to obtain a perfect control.
65

In the context of an automated control system, which controller must be tuned first in a cascade control system?

Правильный ответ:

The secondary controller.

Ваш ответ:

The primary controller.
66

When measuring viscosity with a restricted flow viscometer, the preferred sensing device is:

Ваш ответ правильный:

Capillary tube.
67

The circuit diagrams illustrate four different methods of wiring between a Pt 100 temperature sensor and its signal processing electronics. Which of the wiring methods gives the best measuring accuracy?

Правильный ответ:

Figure 1.

Ваш ответ:

Figure 2.
68

In what kind of measuring equipment might we find a Bourdon-tube?

Правильный ответ:

In a pressure transmitter.

Ваш ответ:

In a flow meter.
69

Which of the following detectors is preferred for detecting smoke from fire?

Правильный ответ:

Ionization type.

Ваш ответ:

Thermocouple.
70

Which type of temperature sensor is used in this temperature measuring system shown?

Ваш ответ правильный:

Thermocouple sensor.
71

Which electronic component or system is this graphical symbol illustrating?

Ваш ответ правильный:

Bandpass filter.
72

Which device does this graphical symbol illustrating?

Ваш ответ правильный:

Pressure to current converter.
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