Accelerometer: Types & Working Principle

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Key Highlights

Accelerometers can be defined as tools that measure proper acceleration.
The device has many uses in the fields of cosmetic products, industry, consumer products, and science.
The accelerometer is divided into three categories: Piezoelectric Accelerometer, Capacitive MEMS Accelerometer and Piezoresistive Accelerometer.
When a body experiences physical acceleration, it is known as proper acceleration.
The basic purpose of any accelerometer is to sense the vibrations and detect the movement of a body.

An accelerometer is an electromechanical instrument that is used to measure the vibration or acceleration of motion of a structure. It also acts as an electromechanical sensor that is used to measure either static or dynamic acceleration.

The working principle of the device involves sensing of all the vibrations produced in the vibrating body.
These vibrations are converted into an effect called the piezoelectric effect, where energy is converted into pressure and stress.
When two or more accelerometers are combined, they can measure the differences in the gradient of the gravitational field.

Table of Content

What is an Accelerometer?
Types of Accelerometer
Working Principle of Accelerometer
Applications of Accelerometer
Sample Questions

Key Terms: Accelerometer, Types of Accelerometer, Proper Acceleration, Acceleration, Piezoelectric Accelerometer, Capacitive MEMS Accelerometer, Piezoresistive Accelerometer

What is an Accelerometer?

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An accelerometer can be defined as an electromechanical device which helps to measure proper acceleration. When acceleration is considered as the rate of change in velocity, proper acceleration explains the acceleration of a body on its own.

Proper acceleration is the acceleration of a body in its own instant state of rest.
The first accelerometer was invented by George Atwood in the 1700s.
It can easily distinguish the different vibrations produced by different bodies.
Every type of accelerometer works on a similar mechanism, which is sensing the vibrations.
They are used in fields like volcanology, consumer electronics, medical science, navigation, cosmetics and transport.
Some accelerometers, which are highly sensitive by nature, are used in inertial navigation systems for missiles and aircraft.
The device is used for the measurement of acceleration forces, such as the force of gravity.

The accelerometer is used when you are watching any series on a mobile app and need to change the mode from landscape to portrait.

Accelerometer

Types of Accelerometer

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The three important types of accelerometers include Piezoelectric Accelerometer, Capacitive MEMS Accelerometer, and Piezoresistive Accelerometer, which are explained in detail below:

Piezoelectric Accelerometer

A piezoelectric accelerometer is a kind of accelerometer that uses the piezoelectric effect of certain materials to calculate the dynamic changes produced in the mechanical variables.

Here, the sensors are made up of crystal structures.
A voltage is created because of the stress due to accelerative forces.
The accelerometer transfers the voltage produced to velocity and direction.

Capacitive MEMS Accelerometer

Capacitive MEMS Accelerometer is a type of accelerometer that is used to detect changes in the working of the capacitance. They are deleted efficiently without being converted to a change in resistance.

If an accelerated force causes movement in the microstructure, then capacitance will change, which will cause the conversion of capacitance to voltage.
The ‘MEMS’ in Capacitive MEMS Accelerometer stands for Micro Electro Mechanical System.
It is a type of fabrication technology.
The most common example of capacitive MEMS accelerometer is mobile phones.

Piezoresistive Accelerometer

The Piezoresistive Accelerometer works as a DC responsive sensor that measures the vibrations produced as an outcome of changes in resistance.

We can use this accelerometer if we want to measure little vibrations like that of a gravity vector.
The device is used to measure high-frequency and high g-shocks.

Working Principle of Accelerometer

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The working principle of the accelerometer is based on the conversion of mechanical energy into electrical energy. When a body, a damped mass, or a proof mass is made to come in contact with a sensor, or when it is placed on one, it starts moving downwards.

As the body gradually moves down, it starts accelerating.
The acceleration gets converted into a significant amount of electric signal.
This signal is used to measure the variations in the position of a device.
The acceleration of the damped mass travels to a specific point such that the spring can push the body mass at the same speed as the casing.
The accelerometers respond differently to different frequencies of acceleration due to damped mass.
It should be noted that the mass and spring oscillations do not affect the required measurements.
Acceleration is measured by measuring force.
The process describes how much a mass presses on something when a force acts on it.

Example: Suppose you are sitting in a moving car when the driver suddenly tries to overtake a truck whose speed is lower than yours. You can experience a slight thud or thump as you move back abruptly into your seat.

This is because the moving car produces acceleration, which produces the forward force.
It gives the impression that we have moved backwards, but in reality, it's not.
Actually, due to motion, the car tries to move away, and we are constantly in our seats, which is why we feel a sudden jerk.

Applications of Accelerometer

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Accelerometers have made their presence crucial and have proved to be essential in many fields. Some of the uses of the device are as follows:

Seismometers are a type of sensitive accelerometers that are used to monitor ground movement such as earthquakes.
They are used in hospitals to measure a patient's chest compressions.
Another category of accelerometer, MEMS, is used in electronic devices such as smartphones, cameras and video-game controllers to detect the movement and orientation of devices.
Accelerometers help measure motion and vibration in cars, safety installations, and buildings.
The device is used in many industrial devices, such as turbines, rotor blades, compressors, and fans.
It records the vibration and helps the user to analyze machines.
They also detect faults quickly before the rotating machines fail utterly.
They are also used in the field of sports to determine the speed and distance of the athlete.
In places worldwide, devices like accelerometer-based step counters are being encouraged to help people stay fit and maintain a healthy lifestyle.
The device also prevents a head collision by being used in football helmets.
It is the most common equipment used for navigation.
They are used in motion sensors and computers to measure the speed of a moving body, its direction, and other things.

Sample Questions

Ques. What is an accelerometer? (2 marks)

Ans. An accelerometer can be defined as a tool that calculates proper acceleration. Proper acceleration is different from acceleration. It means the rate of change of velocity of a body with respect to its own instantaneous rest frame. An accelerometer generally senses or picks up the vibrations produced in a body and helps detect its movement.

Ques. Name the types of accelerometers? (3 marks)

Ans. There are several kinds of accelerometers present. Different accelerometers work differently with each having a unique function. Some of the various kinds of accelerometers used are as follows,

Piezoelectric accelerometer
Shear mode accelerometer
DC Response
High gravity
Capacitive spring mass system base

Ques. How does an accelerometer work? (2 marks)

Ans. The working principle of an accelerometer is based on picking up the vibrations. An accelerometer senses the vibrations being produced in a body and thereby converts this vibration into piezoelectric effect. When some kind of energy is transformed to pressure, piezoelectric effect takes place, or is created. The energy gets converted into electric voltage which in turn helps find out speed and direction of a body.

Ques. Why are accelerometers important? (2 marks)

Ans. Accelerometers are crucial because of their significant contribution to everyday life. They are increasingly used in mobile phones which helps detect their location. They are also known for providing shock which is why they are placed in helmets of footballers to keep their head from injury. Some multi-axis accelerometers also have the ability to find out the speed and direction of proper acceleration.

Ques. What are the different fields where accelerometers are used? (1 mark)

Ans. The use of accelerometers are found in areas like biology, industries, engineering, medical science, gravimetry, volcanology, consumer electronics, navigation, and transport.

Ques. What is a shear mode accelerometer? (2 marks)

Ans. A shear mode accelerometer uses sensing crystals in their mechanism. They are usually smaller in size. Here, the damped mass will apply a force on the shear stress when acceleration is produced. This force in turn, will be applied on the crystals. As a result electrical output is obtained. It is transferred to a circuit of sensors or even a connector. Shear mode accelerometers are associated with generating a high-frequency response.

Ques. How are accelerometers used in medical and navigation? (3 marks)

Ans. In the case of medical purposes, they are devised in such a way that they measure the compressions produced in a patient’s chest. Nowadays, some step counters with the mechanism of accelerometers are also being made for encouraging people to maintain a healthy life and making fitness enthusiasts stick to their regime.

The use of accelerometers has become surprisingly common in the navigation process.
To navigate, they are used in motion sensors to track the correct movement of the body.
They are also used in some special types of rotating sensors to measure by dead reckoning the position.

Ques. What is the difference between accelerometer and gyroscope? (3 marks)

Ans. The difference between accelerometer and gyroscope are as follows:

Accelerometer	Gyroscope
Accelerometer is a device that is used to measure acceleration.	Gyroscope is a device that is used to measure orientation.
It cannot measure angular velocity.	It can measure angular velocity.
The signal to noise ratio in accelerometer is low.	The signal to noise ratio in gyroscope is high.

Ques. How does the accelerometer protect the hard drive of the laptop from damage? (3 marks)

Ans. Accelerometers play an important role in protecting laptop hard drives from damage caused by falls or sudden impacts. They act as a falling sensor and send a signal to the computer's operating system. The operating system interprets the signal from the accelerometer and instructs the hard drive to perform a headpark. The head park will quickly switch off the hard drive to prevent hitting the reading heads into the hard drive platter.

Ques. What is the role of the accelerometer in a smartwatch? (2 marks)

Ans. A sensor that calculates acceleration or the rate at which velocity changes is called an accelerometer. The accelerometer in a smartwatch is used to monitor movement and activity, including steps taken, distance traveled, and energy burned. Additionally, it makes functions like shake-to-wake and wrist movements possible.

Ques. What are the advantages of using an accelerometer? (2 marks)

Ans. The advantages of accelerometer are as follows:

Accelerometers provide a wide frequency range, helping them to capture a broad spectrum of vibrations and accelerations.
Since the device is highly sensitive, it can easily measure small acceleration accurately.
The device is highly durable and robust.
Accelerometer has a fast response time, thus helping capture rapid changes in acceleration accurately.

Accelerometer: Types & Working Principle

Key Highlights

What is an Accelerometer?

Types of Accelerometer

Piezoelectric Accelerometer

Capacitive MEMS Accelerometer

Piezoresistive Accelerometer

Working Principle of Accelerometer

Applications of Accelerometer

Sample Questions

CBSE CLASS XII Related Questions

1.
The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

2.
Write any two features of nuclear forces.

3.
Two small identical metallic balls having charges \( q \) and \( -2q \) are kept far at a separation \( r \). They are brought in contact and then separated at distance \( \frac{r}{2} \). Compared to the initial force \( F \), they will now:

4.
Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.

5.
If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.

6.
What is displacement current (\( i_d \))? Considering the case of charging of a capacitor, show that \( i_d = \varepsilon_0 \frac{d\Phi_E}{dt} \). What is the value of \( i_d \) for a conductor across which a constant voltage is applied?

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Accelerometer: Types & Working Principle

Key Highlights

What is an Accelerometer?

Types of Accelerometer

Piezoelectric Accelerometer

Capacitive MEMS Accelerometer

Piezoresistive Accelerometer

Working Principle of Accelerometer

Applications of Accelerometer

Sample Questions

CBSE CLASS XII Related Questions

1.The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

2. Write any two features of nuclear forces.

3.Two small identical metallic balls having charges \( q \) and \( -2q \) are kept far at a separation \( r \). They are brought in contact and then separated at distance \( \frac{r}{2} \). Compared to the initial force \( F \), they will now:

4.Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.

5. If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.

6.What is displacement current (\( i_d \))? Considering the case of charging of a capacitor, show that \( i_d = \varepsilon_0 \frac{d\Phi_E}{dt} \). What is the value of \( i_d \) for a conductor across which a constant voltage is applied?

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1.
The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

2.
Write any two features of nuclear forces.

3.
Two small identical metallic balls having charges \( q \) and \( -2q \) are kept far at a separation \( r \). They are brought in contact and then separated at distance \( \frac{r}{2} \). Compared to the initial force \( F \), they will now:

4.
Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.

5.
If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.

6.
What is displacement current (\( i_d \))? Considering the case of charging of a capacitor, show that \( i_d = \varepsilon_0 \frac{d\Phi_E}{dt} \). What is the value of \( i_d \) for a conductor across which a constant voltage is applied?