Accelerometer

Accelerometer

An accelerometer is a sensing element that measures acceleration; acceleration is the rate of change of velocity with respect to time. It is a vector that has magnitude and direction. Accelerometers measure in units of g – a g is the acceleration measurement for gravity which is  equal to 9.81m/s². Accelerometers have developed from a simple water tube with an air bubble  that showed the direction of the acceleration to an integrated circuit that can be placed on a  circuit board. Accelerometers can measure: vibrations, shocks, tilt, impacts and motion of an object. 

Types of Accelerometers

There are a number of types of accelerometers. What differentiates the types is the sensing element and the principles of their operation.

Capacitive accelerometers sense a change in electrical capacitance, with respect to acceleration. The accelerometer senses the capacitance change between a static condition and the dynamic state.

Piezoelectric accelerometers use materials such as crystals, which generate electric potential from an applied stress. This is known as the piezoelectric effect. As stress is applied, such as acceleration, an electrical charge is created.

Piezoresistive accelerometers (strain gauge accelerometers) work by measuring the electrical resistance of a material when mechanical stress is applied

Hall Effect accelerometers measure voltage variations stemming from a change in the magnetic field around the accelerometer.

Magnetoresistive accelerometers work by measuring changes in resistance due to a magnetic field. The structure and function is similar to a Hall Effect accelerometer except that instead of measuring voltage, the magnetoresistive accelerometer measures resistance.

Heat transfer accelerometers measure internal changes in heat transfer due to acceleration. A single heat source is centered in a substrate and suspended across a cavity. Thermoresistors are spaced equally on all four sides of the suspended heat source. Under zero acceleration the heat gradient will be symmetrical. Acceleration in any direction causes the heat gradient to become asymmetrical due to convection heat transfer.

MEMS-Based Accelerometers

MEMS (Micro-Electro Mechanical System) technology is based on a number of tools and methodologies, which are used to form small structures with dimensions in the micrometer scale (one millionth of a meter). This technology is now being utilized to manufacture state of the art MEMS-Based Accelerometers.

Future Accelerometer Advancements

In the next decade, NANO technology will create new applications and dramatically reshape this area of technology.

Applications for Accelerometer

From industry to education, accelerometers have numerous applications. These applications range from triggering airbag deployments to the monitoring of nuclear reactors. 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, orientation and the vibration of an object. Accelerometers are becoming more and more ubiquitous: cell phones, computers and washing machines now contain accelerometers.

Other practical applications include:

• Measuring the performance of an automobile

• Measuring the vibration of a machine

• Measuring the motions of a bridge

• Measuring how a package has been handled

Digital accelerometers will give you information using a serial protocol like I2C, SPI or USART, while analog accelerometers will output a voltage level within a predefined range that you have to convert to a digital value using an ADC (analog to digital converter) module.

The digital accelerometer is more sophisticated than the analog. Here the amount of high voltage time is proportional to the acceleration. One of its major advantages is that it is more stable and produces a direct output signal. Accelerometers are now also used in aerospace and many military applications, such as missile launch, weapon fire system, rocket deployment etc. Many a times these accelerometers are used to protect fragile equipment during cargo transportation, and report any strain that might cause a possible damage. Some companies have also managed to develop a wireless 3-axis accelerometers which are not only low in cost but are also shock durable. This 3-axis accelerometer has sensors that are used to protect mobiles and music players. Also these sensors are used in some of the devices used for traffic navigation.

Accelerometer  is consist of five  six pins and we use  five pins for our requirement. These five pins are

1)+vcc

2)Gnd

3) x-axis

4) y-axis

5)z-axis

We connect ++vcc to five volts, and another one is for ground. The remaning pins are connected to the  adc  channels of microcontroller. The output  from  accelerometer is anlog value and we converting these values to digital.

By  tilting the accelerometer device we can find the values that are to be changing in accordance with  accelerometer tilting.