This Portion of Electrical and Electronic Instrumentation contains Primary Sensing Elements and Transducers MCQs (Multiple Choice Questions and Answers) / Objective Type Questions and Answers.
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1. Metal foil type strain gauges are superior to wire wound metal strain gauges because
- They have higher heat dissipation capacity
- They have larger surface area which makes the bonding easier
- They can be fabricated economically using techniques which are similar to those used for fabrication of microelectronic circuitry
- All the above.
D. All the above.
2. Metal foil gauges use fat end turns in order to
- Reduce transverse sensitivity
- Reduce longitudinal sensitivity
- Reduce cross sensitivity
- All the above.
A. Reduce transverse sensitivity
3. In semiconductor strain gauges, the changes in resistance on application of strain
- Is much higher than that in the case of metal strain gauges and this is mainly due to change in dimensions
- Is much higher than that in the case of metal strain gauges and this is mainly due to change in resistivity
- Is lower than that in the case of metal strain gauges
- None of the above.
B. Is much higher than that in the case of metal strain gauges and this is mainly due to change in resistivity
4. In semi-conductor strain gauges, when tensile strain is applied
- Resistance increases in N-type of materials
- Resistance increases in P-type of materials
- Resistance increases in both P and N type of materials
- Resistance decreases in both P and N type of materials
B. Resistance increases in P-type of materials
5. The RTDs use the principle of change of resistance with temperature. The properties of a conductor materials to be used as an element of an RTD should possess the following properties
- The change in resistance per unit change in temperature should be as small as possible
- The resistance of materials should not have a continuous and stable relationship with temperature
- The change of resistance with temperature should not be a linear function
- None of the above.
D. None of the above.
6. Platinum is the commonly used metal for RTDs this is because
- Platinum has a constant value of resistance temperature co-efficient of 0.004°C for a temperature range between 0 to 100°C
- The resistivity of platinum tends to increase less rapidly at higher temperatures
- Platinum is available in pure form for commercial applications and has a stability over higher ranges of temperature
- All the above.
D. All the above.
7. The resistance of thermometer is 5 Ω at 30°C and 6.5 Ω at 60°C. using linear approximation, the value of resistance temperature co-efficient at 45°C
- 0.009/°C
- 0.0087/°C
- 0.0085/°C
- 0.01/°C.
B. 0.0087/°C
8. The sensitivity of thermistors as compared with sensitivity of platinum resistance temperature detector over a temperature range of -100°C to 400°C to changes in temperature is
- 100 times
- 106 times
- 107 times
- 100 times
B. 106 times
9. A thermistor exhibits
- Only a negative change of resistance with increase in temperature
- Only a positive change of resistance with increase in temperature
- Can exhibits either a negative or positive changes of resistance with increase of temperatures depending upon the type of materials used
- None of the above.
C. Can exhibits either a negative or positive changes of resistance with increase of temperatures depending upon the type of materials used
10. The resistance value of thermistor is 5000Ω at 25°C and its resistance temperature co-efficient is 0.04/°C. A measurement with a lead resistance of 10 Ω will cause an error of
- 0.02°C
- 0.05°C
- 0.1°C
- None of the above.
B. 0.05°C
11. The temperature transducers exhibits non-linear behavior. The order in which they exhibits non-linearity (highest to lowest) is
- Thermocouples, RTDs, thermistors
- Thermistors, thermocouples, RTDs
- RTDs, thermocouples and thermistors
- Thermistors, RTDs, thermocouples.
B. Thermistors, thermocouples, RTDs
12. Three types of temperature transducers are compared as regard their sensitivity. The order in which they exhibits their sensitivities (highest to lowest ) is
- Thermistors, RTDs, thermocouples.
- Thermocouples, RTDs, thermistors
- RTDs, thermistors , thermocouples
- RTDs, thermocouples and thermistors
A. Thermistors, RTDs, thermocouples.
13. Thermocouples are passive
- Passive transducers
- Active transducers
- Both active and passive transducers
- Output transducers
B. Active transducers
14. Thermocouples
- Are most commonly used temperature transducers
- Require reference junction compensations
- Have a low output voltage level
- All the above.
D. All the above.
15. A thermocouples produces a voltage of 50mV. Its internal resistance is 50Ω. The resistance of its lead is 10 Ω.its ouput is read by a PMMC meter having an internal resistance of 120 Ω. The output voltage indicated is
- 33.3 mV
- 25 mV
- 40 mV
- 10 mV.
A. 33.3 mV
16. Air cored inductive transducers are suitable for use
- At lower frequencies
- At higher frequencies
- At equal frequencies
- As are applied for iron cored transducers
B. At higher frequencies
17. The side of air cored transducers as compared ith their iron cored counterparts is
- Smaller
- Bigger
- Same
- All the above.
B. Bigger
18. An iron core transducer is exited with a frequency of 20KHz. The maximum value of frequency of displacement to be measured with this transducer should not exceed
- 0.5 kHz
- 1 kHz
- 1.5 kHz
- 2 kHz
D. 2 kHz
19. Inductive transducers are used in differential configuration because the output is not influenced by
- External magnetic fields
- Temperature changes
- Variation of supply voltages and frequency
- All the above.
D. All the above.
20. Two inductive transducers working on the principle of change of self inductance L, are connected in push pull arrangement. If the change of inductance of transducers is the change of inductance exhibited at the output terminals is
- ∆L
- 2∆L
- ±2∆L
- zero
C. ±2∆L
21. In an LVDT the two secondary winding are connected in differential to obtain
- Higher output voltage
- An output voltage which is phase sensitive i.e the output voltage has a phase which can lead is to a conclusion whether the displacement of the core took place from right to left or from left to right
- In order to establish the null or the reference point for the displacement of the core
- Both (b) and (c)
D. Both (b) and (c)
22. In an LVDT the core is made up of a
- Non-magnetic material
- A solid ferro-electric material
- High permeability, nickel-iron haydrogen annealed material in order to produce low harmonics, low null voltage, and high sensitivity. The core is slotted to reduce eddy current losses
- All the above.
C. High permeability, nickel-iron haydrogen annealed material in order to produce low harmonics, low null voltage, and high sensitivity. The core is slotted to reduce eddy current losses
23. An LVDT
- Exhibits linear characteristics up to a displacement of ± 5 mm
- Has a linearity of 0.05%
- Has an infinite resolution and a high sensitivity which is of the order of 40V /mm
- All the above.
D. All the above.
24. An LVDT
- Has a very good frequency response as the mass of the core to which the input signal is applied is fairly large
- Is immune to stray magnetic fields
- Has a zero voltage at the null point even if the supply voltage contains and harmonics and even if the two secondary windings are not exactly similar and even asymmetrically placed with respect to primary winding
- None of the above.
D. None of the above.
25. There are two modes in which synchro transmitter-transmitter pair are used i.e (i) error detection mode (ii) torque transmission mode. The torque in the torque transmission mode
- Is greater than that in the error transmission mode
- Is smaller than that in the error transmission modes
- The torque is same in both the modes
- None of the above.
B. Is smaller than that in the error transmission modes
26. The rotor of a synchro-transmitter
- Uses a silent pole type of construction
- Uses a cylindrical pole type of construction
- May use either silent pole or cylindrical type of construction
- None of the above.
A. Uses a silent pole type of construction
27. The electrical zero of synchro-transmitter is when voltage induced
- In coil S1, of stator is maximum
- In coil S3, of stator is maximum
- In coil S2, of stator is maximum
- In coil S2, of stator is maximum and the voltage across terminals S3, S1, is zero.
D. In coil S2, of stator is maximum and the voltage across terminals S3, S1, is zero.
28. The electrical zero of a synchro-transformer is
- Displaced by an angle 180° from the zero of a syncro-transmitter
- Displaced by an angle 90° from the zero of a syncro-transmitter
- Displaced by an angle 0° from the zero of the transmitter
- None of the above.
B. Displaced by an angle 90° from the zero of a syncro-transmitter
29. In a synchro-tranmitter, the voltage induced in the three windings of the stator are
- Displaced 120° in time phase
- Are in phase with each other
- Displaced 90° in time phase
- None of the above.
B. Are in phase with each other
30. When a synchro-transmitter synchro control transformer pair is used as an error detector the ouput voltage obtained from the rotor terminals of
- Sinusoidal
- Suppressed carrier modulated
- Half wave rectified
- None of the above.
B. Suppressed carrier modulated
