Which of the following statements are correct A. Megnetostrictive transducer operation depends on the change of permeability of magnetic material is when strained. B. Potentiometer is an active transducer. C. Turbine flow meters are volumetric flow meters D. Any metal can be thermistor. E. Thermocouples are used in high accuracy measurements. Choose the most appropriate answer from the options given below :
A and C only
Judge each statement against standard transducer theory.
A — "Magnetostrictive transducer operation depends on the change of permeability of a magnetic material when strained." TRUE. This is the Villari effect (inverse magnetostriction): applying mechanical stress to a ferromagnetic material such as nickel or Terfenol-D changes its permeability, which changes the inductance of a surrounding coil and hence gives an electrical output. The forward effect — a magnetic field producing strain (Joule magnetostriction) — is what drives ultrasonic transducers and sonar projectors.
B — "Potentiometer is an active transducer." FALSE. The classification is by energy source: an active (self-generating) transducer produces its own output energy — thermocouple, piezoelectric crystal, photovoltaic cell, tachogenerator. A passive transducer merely varies a circuit parameter and needs external excitation — resistance (potentiometer, strain gauge, RTD, thermistor), capacitance, or inductance (LVDT). A potentiometer is a variable resistance and needs a supply, so it is passive.
C — "Turbine flow meters are volumetric flow meters." TRUE. The rotor speed is proportional to the average fluid velocity, and multiplying by the fixed bore area gives volume per unit time:
\(Q = A v \propto N\)
where N is the rotational speed picked up by a magnetic sensor. To obtain mass flow you must additionally know the density (a Coriolis meter measures mass flow directly).
D — "Any metal can be a thermistor." FALSE. A thermistor is made from sintered semiconductor metal oxides (of manganese, nickel, cobalt, iron), which give a large negative temperature coefficient and a strongly non-linear response. Metals behave in the opposite way — a small, nearly linear positive coefficient — which is what makes them suitable for RTDs (platinum Pt-100), not thermistors.
E — "Thermocouples are used in high accuracy measurements." FALSE as keyed. Thermocouples are prized for their very wide range, ruggedness, small size and fast response, but their millivolt-level output, non-linearity and need for cold-junction compensation make them less accurate than a platinum RTD, which is the standard choice where accuracy matters.
Hence, the correct answer is A and C only.
Similar Questions
Which of the following statements are correct ?
A. Hygrometer measures the value of humidity directly
B. Hygrometer measures the value of humidity indirectly
C. Wien's bridge is used to measure the frequency of the signal
D. Wien's bridge is used to measure the amplitude of the signal
E. Bimetallic strip is a thermal expansion detector.
Choose the most appropriate answer from the options given below :
Match List I with List II
LIST I LIST II A. Stroboscope I. Changes its electrical resistance with temperature B. Bolometer II. Generate thermoelectric emf C. Thermocouple III. Changes pressure to displacement D. Diaphragm IV. For measurement of rotary motion Choose the correct answer from the options given below:
Match the following lists :
List – I List – II a. Electromechanical Device i. Seismic Device b. Optical Device ii. Piezo-electric c. Gyroscopic device iii. Interferometers d. Absolute motion device iv. Aerospace vehicle Choose the correct answer from the codes given below:
Consider the following transducers or transducer systems :
(a) Float elements
(b) Seismic system
(c) Gyroscope
Arrange the above transducers/systems in decreasing order of the availability of possible number of output signals.
Consider the following statements associated with electrical and electronic transducers
A. Little power is consumed by transducer
B. Mass intertia effects are not minimized
C. The response time is small
D. Transmission and processing the signal for the purpose of measurement are easier.
Choose the correct answer from the options given below:
Match List I with List II
LIST I LIST II A. Relative error I. The ability of tde device to give identical O/P when repeated measurements are made witd tde same I/P signal B. Precision II. The ratio of difference between measured value and tde true value to tde true value of tde measurand C. Caliberation III. The smallest increment in measure tdat can be detected witd certainity by tde instrument D. Resolution IV. The process of making adjustments or tde scale so tdat tde instrument reading conform to an accepted standard. Choose the correct answer from the options given below:
The fundamental law that is used in temperature measurement is known as
Assertion (A) : Normally, some standard signal conditioner and display devices are used with a transducer, unless they are custom-built to suit the requirements of the transducers.
Reason (R) : A transducer is a device which receives energy in one form and transfer it to a convenient form.
Select your answer using the codes given below :
Which of the following transducers are not linear ?
i. thermistor
ii. thermocouple
iii. IC sensorWhich of the following sensors has excellent linearity ?
Important Questions from Basics of Transducers
Which of the following can act as an inverse transducer?
For transducers, following statements are given:
(A) An optical interferometer is useful for measuring extremely small motions
(B) The damping ratio of a seismic instrument should be low for good dynamic performance
(C) A rate gyro is a relative motion measuring device
(D) A pneumatic motion transducer is non-linear over a wide range of motion
(E) A piezoelectric accelerometer can only be used for static motion measurement
Choose the correct answer from the options given below:
Choose the INCORRECT statement with respect to the use of electrical transducers.
Consider the following transducers:
1. LVDT
2. Piezoelectric
3. Thermocouple
4. Photovoltaic cell
5. Strain gauge
Which of these are active transducers?
Under which condition, Transducers must operate?
