# Biomedical Instrumentation Questions and Answers – Displacement, Position and Motion Transducers

«
»

This set of Biomedical Instrumentation Questions and Answers for Freshers focuses on “Displacement, Position and Motion Transducers”.

1. Potentiometer works on which of the following principle?
a) variable resistance
b) variable inductance
c) variable capacitance
d) variable electromagnet

Explanation: Potentiometer works on the principle of variable resistance. The resistance between two terminals of this device is related to the linear or angular displacement of a sliding tape along a resistance element. When the fixed terminals of the potentiometer are connected to the power supply. Either ac or dc, output voltage at the wiper varies with the displacement of the object.

2. On increasing the distance between the plates of a variable capacitor, the displacement- capacitance characteristics changes _______
a) proportionally
b) linearly
c) exceptionally
d) hyperbolically

Explanation: By moving one plate of the capacitor with respect to the other, the capacitance will vary inversely with respect to the plate separation. This will give a hyperbolic displacement capacitance characteristic. This is how variable capacitance is employed as displacement transducers.

3. Lateral displacement of capacitance plates with respect to each other gives linear displacement capacitance characteristics.
a) True
b) False

Explanation: It is true that lateral displacement of capacitance plates with respect to each other gives linear displacement capacitance characteristics. C = 0.0885*k*(A/d).
k = dielectric constant of the medium separating the two plates.
C = capacitance in micro farads
A = area of each identical plate in cm2
d = distance between the plates in cm2.

4. LVDT stands for _________
a) Linear Virtual Double Transformer
b) Linear Virtual Differential Transducer
c) Linear Variable Differential Transducer
d) Linear Variable Differential Transformer

Explanation: LVDT stands for Linear Variable Differential Transformer. These transducers are conventionally used for measurement of physiological pressure. They generally work in conjunction with carrier amplifiers.

5. LVDT works on the principle of ________
a) variable resistance
b) variable inductance
c) variable capacitance
d) variable pressure

Explanation: LVDT works on the principle of variable inductance. It has three coils namely the primary coil which is the center coil. The other two are called the secondary coils so connected that their outputs are equal in magnitude but opposite in phase.

6. In LVDT the secondary coils are energized with sine wave oscillator.
a) True
b) False

Explanation: The center coil is the energizing or primary coil connected to a sine wave oscillator. The secondary coils so connected that their outputs are equal in magnitude but opposite in phase. LVDT works on the principle of variable inductance.

7. How many coils are required to make LVDT?
a) 4
b) 6
c) 3
d) 2

Explanation: Total 3 coils are required in LVDT. One centered coil which is the energizing or primary coil connected to the sine wave oscillator. The other two coils are the secondary coils so connected that their outputs are equal in magnitude but opposite in phase.

8. LVTD is a _______ transducer.
a) displacement
b) photoelectric
c) thermal
d) chemical

Explanation: LVDT is a displacement transducer. It works on the principle of variable inductance. The shift in the ferromagnetic core from the centre position induces voltage in the second coil which can be calibrated to determine the linear displacement.

9. Which of the following is a displacement transducer?
a) Thermistor
b) LVDT
c) Strain gauge
d) Thermocouple

Explanation: LVDT is a displacement transducer. Thermocouple and thermistor are temperature transducers. Strain gauge is a pressure transducer.

10. Linear encoders gives ___________ output.
a) angular
b) analog
c) digital
d) unstable 