# Mechatronics Questions and Answers – Proximity Sensors

This set of Mechatronics Multiple Choice Questions & Answers (MCQs) focuses on “Proximity Sensors”.

1. Which type of material can be sensed by inductive proximity sensor?
a) Wooden type
b) Metallic type
c) Plastic type
d) Glass type

Explanation: Metallic type of material can be sensed by inductive proximity sensor. Inductive proximity sensor works on the principle of electromagnetic induction, that is it creates a magnetic field which induces an emf(electromotive force) which used to determine the presence of objects.

2. Will an infrared proximity sensor detect a black object when it comes in suitable range?
a) Yes, It will detect the object
b) No, It will not detect the object
c) Yes but it will produce random output
d) The sensor will stop working

Explanation: No, It will not detect the object if a black object comes in the range of an infrared proximity sensor. Since infrared proximity sensors work on reflection of Infrared ray from the objects but when these rays hit a black object, the ray gets absorbed and does not bounce back. So the sensor is unable to detect the object.

3. Which is the emf(electromotive force) induced in a coil if it has 8 turns and rate of change of flux with respect to time is 0.5?
a) -10 V
b) -25 V
c) 5.5 V
d) -4 V

Explanation:Given:
Number of turns(N)=8
Change of flux with respect to time(dΦ/dt)=0.5
Emf(electromotive force)(e)=-N*(dΦ/dt)
e=>-8*0.5=-4 V
-4 V is the emf (electromotive force) induced in a coil if it has 8 turns and rate of change of flux with respect to time is 0.5.

4. Which metal will have a larger range of detection by inductive proximity sensor?
a) Iron
b) Aluminium
c) Copper

Explanation: Iron will have a larger range of detection by inductive proximity sensor. A ferrous metal enables a longer range of detection where as non-ferrous metals can reduce the sensing range by 60%. Iron is a ferrous metal whereas all others are non-ferrous which is why iron will have a longer range of detection.

5. A proximity sensor requires physical contact.
a) True
b) False

Explanation: A proximity sensor does not require any physical contact. It can detect objects at distant places without a touch or contact. It uses electromagnetic waves for the detection. Most of the proximity sensor uses infrared waves for detection.
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6. An inductive proximity sensor cannot detect a metallic object if it is wet or dirty.
a) True
b) False

Explanation: An inductive proximity sensor can detect a metallic object even if it is wet or dirty. Inductive proximity sensor works on the principle of electromagnetic induction, that is it creates a magnetic field which induces an emf (electromotive force) which used to determine the presence of objects. The water and dirt does not interfere the magnetic field so it can detect a metallic object even if it is wet or dirty.

7. Which is has the number of turns in a coil if the emf (electromotive force) induced in it is -2.5V and rate of change of flux with respect to time is 0.5?
a) -1.5 V
b) -2.5 V
c) 5.5 V
d) -3 V

Explanation:Given:
Emf(electromotive force) induced in it is -2.5V
Change of flux with respect to time(dΦ/dt)=0.5
Emf(electromotive force)(e)=-N*(dΦ/dt)
-2.5=-N*0.5
N=5
Therefore, the coil has total 5 turns.

8. Inductive sensors are also referred as “NMR” coils. What does NMR stand for?
a) Nuclei Magneto resonance
b) Nuclei Magnetic resonator
c) Nuclear Magnetic resonator
d) Nuclear Magnetic resonance

Explanation: NMR stands for Nuclear Magnetic resonance. The “NMR (Nuclear Magnetic resonance)” coils detect the magnetic component of the EM (Electro-magnetic )field linked with the nuclear spin precession in Nuclear Magnetic resonance.

9. Which metal will have a larger range of detection by inductive proximity sensor?
a) Zinc
b) Steel
c) Copper

Explanation: Steel will have a larger range of detection by inductive proximity sensor. A ferrous metal enables a longer range of detection where as non-ferrous metals can reduce the sensing range by 60%. Steel is a ferrous metal whereas all others are non-ferrous which is why Steel will have a longer range of detection.

10. Which is an example of infrared proximity sensor?
a) GP2Y0A41SK0F
b) CMCP793V-500
c) SLB700A/06VA
d) BMP180

Explanation: GP2Y0A41SK0F is an example of infrared proximity sensor. It is used for detecting object in short range. BMP180 is an example of pressure sensor. SLB700A/06VA is an example of force sensor. CMCP793V-500 is a velocity sensor.

11. Which is the emf (electromotive force) induced in a coil if it has 10 turns and rate of change of flux with respect to time is 1?
a) -10 V
b) -25 V
c) 5.5 V
d) -3 V

Explanation:Given:
Number of turns(N) = 10
Change of flux with respect to time(dΦ/dt)=1
Emf(electromotive force)(e)=-N*(dΦ/dt)
e=>-10*1=-10 V
-10 V is the emf (electromotive force) induced in a coil if it has 10 turns and rate of change of flux with respect to time is 1.

12. A capacitive proximity sensor can detect only metallic object.
a) True
b) False

Explanation: A capacitive proximity sensor can also detect other object other than just metallic object. It can detect all objects that have a dielectric constant other than air. These type of sensors are widely used in appliances such as track-pads or touch-screen sensors.

13. A proximity sensor does not work if the temperature exceeds 100 degree Celsius.
a) True
b) False

Explanation: A proximity sensor can work even if the temperature exceeds 100 degree Celsius. They can work on a wide temperature range which may extends from -40 degree Celsius to 200 degree Celsius and even more. They can work accurately at any temperature within this range.

14. Which type of proximity sensor can be used as touch sensor?
a) Inductive proximity sensor
b) Capacitive proximity sensor
c) Ultrasonic proximity sensor
d) Photoelectric proximity sensor

Explanation: Capacitive proximity sensor can be used as touch sensor. Capacitive proximity sensors can detect all objects that have a dielectric constant other than air. When a human finger comes in contact to the sensor, it immediately responds to this touch.

15. Which type of proximity sensor can detect a magnetic substance even if a wall of non-ferrous substance is made?
a) Magnetic proximity sensor
b) Capacitive proximity sensor
c) Ultrasonic proximity sensor
d) Photoelectric proximity sensor

Explanation: Magnetic proximity sensor can detect a magnetic substance even if a wall of non-ferrous substance is made. It can detect the objects beyond the normal limit of inductive proximity sensor. Since magnetic field can penetrate any wall made of ferrous substance, so they can easily detect a magnetic substance placed beyond the wall.

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