What is an accelerometer and why do we need accelerometers?
An accelerometer is a device that can be used to measure vibration and shock. The accelerometers that are widely used are strain gauge and piezoelectric type accelerometers. An accelerometer is basically a motion sensor, it can measure the acceleration of an object. We can use accelerometers to measure the vibration and shock, so in case if the vibration level increases then we can prevent it. The vibrations and shocks can be seen in motors, turbines, machine tools, etc. The accelerometer is an electromechanical device and it can detect the acceleration force of an object. The detected force could be static or dynamic, this device can detect the absolute or relative acceleration of a device
The accelerometers are used for vibration monitoring so they can be used to check the industrial machines and this would save money and also improves the life of machines in the industry. The accelerometer can improve plant safety it can detect certain conditions such as shaft misalignment, rotor imbalance, gear failure, and also it can determine the bearing failure. So by checking the vibration of the equipment in a plant the accelerometer detects the faults before the equipment failure.
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What is the use of accelerometers?
By using an accelerometer we can detect the angle at which the device moves and we can also determine the way in which the object is moving. This device can be used to check the vibration levels and also the acceleration of an object can be determined too. This device is widely used to measure the tilt, inertial force, shock, and vibration. We can see accelerometers in automotive, medical, industrial control, and other applications. We can consider an accelerometer as the major motion sensor, the accelerometer is composed of a sensor that is capable to provide the acceleration, speed, velocity, and also the position information.
How does an accelerometer work?
There are many types of accelerometer and they work in different ways, some accelerometer operates by the piezoelectric effect. So this type of accelerometer uses a piezoelectric crystal and this crystal would get stressed from the accelerative forces and this would cause to generate a voltage and this will be proportional to the force. There is another type of accelerometer that makes the use of capacitance to do its operation and in the capacitance type accelerometers, it would have two microstructures. These microstructures are placed close to each other and there would be capacitance between them so if any of the microstructures is moved by the accelerative force then the capacitance would change and the change in capacitance is converted into a voltage by the circuitry. There are other types of accelerometers that use the piezo-resistive effect and hot air bubbles to do the operation.
What are the types of accelerometers and how do they work?
In this type of device, the major part is a piezoelectric material, one portion of this device is connected to a rigid post at the sensor base, and the other part is attached to a seismic mass. So if there is any vibration a force will be created in the piezoelectric material and this force will be equal to the acceleration of the seismic mass, because of the piezoelectric effect a charge output proportional to the applied force is generated. If the seismic mass is reduced then we could get a good operating frequency range and also the resonance frequency can be increased.
This type of accelerometer has the same working principle as the piezoelectric accelerometer and the only difference is that this device uses a resistive substrate instead of a piezoelectric crystal. So during the vibration, the force would affect the seismic mass and due to this the resistance of the etched bridge network would change and this will be detected. This type of accelerometers has a good bandwidth range. These types of accelerometers are widely used to measure the shock.
The major part of a capacitive accelerometer is a pair of capacitor plates and these plates act in a differential mode. The capacitor accelerometer is composed of a diaphragm and this diaphragm would be affected by the acceleration, or force due to it. The diaphragm is situated between the two plates and the diaphragm is situated as a moving plate between them. The force would change the distance between the two plates and it would change the capacitance.
This type of motion sensor can sense the variation in the electrical capacitance according to the acceleration. The sensing element would operate in a bridge circuit with the two fixed capacitor. The voltage would vary by the capacitor if the structure accelerates.
Hall effect accelerometers
In this type of accelerometer, the hall-effect principle is used for its operation, hall-effect can be described as if a conductor is in a magnetic field and when a current is applied to the conductor, then a voltage would be generated due to the current and magnetic field and this generated voltage will be perpendicular to both the current and magnetic field.
So in a hall effect accelerometer, the hall element is connected to a spring with a seismic mass and it would deflect because of the force. The hall element would move because of the force and a voltage is generated which will be proportional to the acceleration. This type of sensor is not affected by dust.
This type of accelerometers operates by measuring the changes in resistance due to a magnetic field. This type of accelerometer has the same function and structure as a hall-effect accelerometer, and the difference between them is the magnetoresistive accelerator measures resistance instead of voltage.
Heat transfer accelerometer
This type of accelerometer operates according to the principle of convection. This device would measure the internal changes in heat transfer that is caused by the acceleration. This type of accelerometer doesn’t use a solid seismic mass instead of that it uses gas and because of this, there won’t be any stiction or particle contamination.
This device has a heat source and the aluminum thermocouples are placed around the heat source. So if there is no force then the thermocouples temperature won’t vary and the output voltage of the thermocouple would be the same. But if there is force in any direction then we can see the variation in the temperature. Because of the convection heat transfer could occur and the output of the thermocouple would vary.
How to select an accelerometer?
- We must check the dynamic range and sensitivity
- The frequency range must be checked
- This sensor must be selected according to the environment
- It must be selected according to the mounting method
- It can be selected according to the required output like analog or digital
- Sensitivity must be considered
- The maximum swing must be considered too
What are the advantages of piezoelectric accelerometers?
- It doesn’t have any moving part
- Compact in size and they are robust
- High stability
- It doesn’t need any power supply
- High dynamic and frequency range
What are the applications of accelerometer?
- Vibration and shock measurements in machines, process control systems, cars, etc.
- It is used in electronic devices
- It can be used to determine the seismic activity
- It is used for orientation sensing
- It can be used to measure the gravitational field
- It can be used to determine the vehicle acceleration
- It is used in many industries to check the rotating machines such as pumps, compressor, and cooling tower
- Automotive manufacturing plants
- Power plants
- Food and beverage