Accelerometers | Working , Advantages and Applications

What is an accelerometer?

An accelerometer is an electromechanical device that will measure acceleration forces. These forces may be static, like the constant force of gravity pulling at your feet, or they could be dynamic – caused by moving or vibrating the accelerometer.

What are accelerometers useful for?
By measuring the amount of static acceleration due to gravity, you can find out the angle the device is tilted at with respect to the earth. By sensing the amount of dynamic acceleration, you can analyze the way the device is moving. At first, measuring tilt and acceleration doesn’t seem all that exciting. However, engineers have come up with many ways to make really useful products with them.

An accelerometer can help your project understand its surroundings better. Is it driving uphill? Is it going to fall over when it takes another step? Is it flying horizontally or is it dive bombing your professor? A good programmer can write code to answer all of these questions using the data provided by an accelerometer. An accelerometer can help analyze problems in a car engine using vibration testing, or you could even use one to make a musical instrument.

In the computing world, IBM and Apple have recently started using accelerometers in their laptops to protect hard drives from damage. If you accidentally drop the laptop, the accelerometer detects the sudden freefall, and switches the hard drive off so the heads don’t crash on the platters. In a similar fashion, high g accelerometers are the industry standard way of detecting car crashes and deploying airbags at just the right time.

WHAT ARE THE DIFFERENT TYPES OF ACCELEROMETER ?

There are many different type of accelerometers and each has unique characteristics, advantages and disadvantages. The different types include:

Different technologies

Piezo-electric accelerometers
Piezo-resistive accelerometers
Strain gage based accelerometers

Different output accelerometers

Charge output
Voltage output (3 wire)
4-20mA output
Velocity output accelerometers

Different designs of accelerometer

Shear type design
Single ended compression design
Isolated compression
Inverted compression
Flexural design

How do accelerometers work?
There are many different ways to make an accelerometer! Some accelerometers use the piezoelectric effect – they contain microscopic crystal structures that get stressed by accelerative forces, which causes a voltage to be generated. Another way to do it is by sensing changes in capacitance. If you have two microstructures next to each other, they have a certain capacitance between them. If an accelerative force moves one of the structures, then the capacitance will change. Add some circuitry to convert from capacitance to voltage, and you will get an accelerometer. There are even more methods, including use of the piezoresistive effect, hot air bubbles, and light.

Advantages:

Available in numerous designs (such as compression, shear, and strain gage), sizes, weights, and mounting arrangements (such as center, stud, screw mounted, and glue-on). Ease of installation is also an advantage.
Accelerometers are available for high-temperature environments
(up to 1,200”F).
Wide band frequency and amplitude response.
Accelerrnneters are available for high frequency and low Durable, robust construction and long-term reliability. frequency (down to DC) measuring capabilities.

Disadvantages:

Require contact with (mounting upon) the object being measured. Therefore, the mass of the accelerometer must be small relative to this object (generally should be less than 5% of mass of vibrating component being measured).
Sensitive to mounting (must be mounted securely).
Sensitive to cable noise and “whip” (change in cable capacitance caused by dynamic bending of the cable).
Results are not particularly reliable when displacement is calculated by double integrating (electronically) the acceleration signal.

APPLICATIONS OF ACCELEROMETERS
Accelerometers are one of those sensors which find numerous applications in academia as well as in large number of industries. These applications range from airbag sensor in automotive applications to monitoring vibrations on a bridge and in many military and space systems. There are a number of practical applications for accelerometers; accelerometers are used to measure static acceleration (gravity), tilt of an object, dynamic acceleration, shock to an object, velocity, and the vibration of an object. Accelerometers are being used nowadays in mobile phones, laptops, washing machines, etc